Pesticide Chemistry in the 20th Century: A Symposium sponsored by the Division of Pesticide Chemistry at the 171st Meeting of the American Chemical Society, New York, April 6 - 8, 1976

Pesticide Chemistry in the 20th Century Jack R. Plimmer, EDITOR United States Department of Agriculture

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.fw001

ASSOCIATE EDITORS

Philip C . Kearney Gustave Κ . Kohn Julius J. Menn Stanley Ries

A symposium sponsored by the Division of Pesticide Chemistry at the 171st Meeting of the American Chemical Society, New York, N.Y., April 6 - 8 , 1976.

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ACS SYMPOSIUM SERIES

AMERICAN

CHEMICAL

WASHINGTON, D. C. 1977

SOCIETY

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.fw001

Library of Congress CIP Data Pesticide chemistry in the 20th century. (ACS symposium series; 37 ISSN 0097-6156) Includes bibliographical references and index. 1. Pesticides—Congresses. 2. Agricultural chemistry— Congresses. 3. Insect hormones—Congresses. 4. Plant regulators—Congresses. I. Plimmer, Jack R., 1927II. American Chemical Society. Division of Pesticide Chemistry. III. Series: American Chemical Society. ACS symposium series; 37. SB951.P393 ISBN 0-8412-0364-4

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American Chemical Society A l l Rights Reserved. N o part of this book may be reproduced or transmitted in any form or by any means—graphic, electronic, including photocopying, recording, taping, or information storage and retrieval systems—without written permission from the American Chemical Society. PRINTED IN THE UNITED STATES OF AMERICA

ACS Symposium Series

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.fw001

Robert F. G o u l d , Editor

Advisory Board Donald G. Crosby Jeremiah P. Freeman E. Desmond Goddard Robert A. Hofstader John L. Margrave Nina I. McClelland John B. Pfeiffer Joseph V. Rodricks Alan C. Sartorelli Raymond B. Seymour Roy L. Whistler Aaron Wold

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FOREWORD The ACS SYMPOSIUM SERIES was founded in 1974 to provide

a medium for publishing symposia quickly in book form. The format of the SERIES parallels that of the continuing ADVANCES IN CHEMISTRY SERIES except that in order to save time the papers are not typeset but are reproduced as they are submitted by the authors in camera-ready form. As a further means of saving time, the papers are not edited or reviewed except by the symposium chairman, who becomes editor of the book. Papers published in the ACS SYMPOSIUM SERIES are original contributions not published elsewhere in whole or major part and include reports of research as well as reviews since symposia may embrace both types of presentation.

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PREFACE The papers in this volume were presented at the Centennial Meeting of the American Chemical Society held in New York in April 1976. They were delivered at the Symposium "Pesticide Chemistry in the Twentieth Century," sponsored by the Division of Pesticide Chemistry. Although the division was not formed until 1969, pesticide chemistry had previously been an enthusiastically supported activity within the Division of Agriculture and Food Chemistry. The symposium title was chosen to provide some discussion of the development of pesticide chemistry, and also because the growth in use of synthetic organic pesticides is a peculiarly twentieth century phenomenon. Thus, three quarters of the way through the present century seemed an opportune time to record something of the past and to speculate as to the future role and direction of pesticide chemistry. Many of those associated with the early growth and development of synthetic organic pesticides are still active and continue to influence their development. The centennial meeting provided the appropriate occasion for authoritative overview and personal expression of scientific philosophy. Side by side with this growth of knowledge there has been increasing concern that the implications of the large-scale utilization of synthetic chemicals be fully understood. Chemical methods of pest control have conferred such spectacular benefits on agriculture and the health of mankind that it has become difficult to conceive that these benefits could be offset or outweighed by serious disadvantages. Some of these effects are extremely subtle; others, such as the development of pesticide resistance, rapidly become obvious because no further economic benefit is obtained by continued pesticide use. The extensive use of pesticides has grown out of the experimental and intellectual achievements of nineteenth century organic chemistry. Naturally occurring organic compounds such as nicotine have long been known to possess insecticidal activity, but the large-scale use of synthetic organic compounds for pest control is a twentieth century phenomenon. During the last 25 years we have experienced a phenomenal expansion in the production and use of synthetic organic pesticides, especially by the developed nations of the world. We have also learned to assess the relative risks and benefits that accompany their use. Scientifically, we have learned a great deal; the investigation of the metabolism of pesticides, their modes of action, chemical reactions, analysis, and many vii

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similar studies have been .productive of excellent research whose relevance extends far beyond its immediate application to pest control. We now look back to pesticide chemistry of the 1940s and 50s as though we were looking back to the days of the covered wagon. Until the end of those decades, gas chromatography was little used, and methods of residue analysis were often difficult and tedious. With the application of gas chromatography has come the potential for rapid and economical measurement of low-level pesticide residues. Our current knowledge of environmental pesticide levels is based on this technique, and it has provided a guide for the investigation of many other environmental contaminants. Although we have recognized many of the major problems that have been associated with pesticide chemicals in the past, there is the chance that their shadow may extend well into future decades. Science faces the challenge of establishing the effects of pesticides on many different organisms, the nature and extent of pesticide transformations in the environment, and the environmental fate of xenobiotics. The cost of this research may hinder the development of new compounds very different in chemistry or mode of action from those currently on the market, but we recognize its necessity. We are passing through what may be a critical phase in the use and production of chemicals for pest control, and to remedy this problem we must devise and improve techniques by which the toxicology and environmental fate of new chemicals and products can be evaluated rapidly and economically. An additional challenge is to look beyond our present use of pesticide chemicals and discover new modes of action or new ways of employing chemicals to minimize their effects on the environment and on nontarget species. Since the discovery of hexachlorobenzene by Faraday, more than 150 years have elapsed. The recognition of the insecticidal activity of the organochlorine compounds and the pursuit of new active structures represents one of the triumphs of synthetic organic chemistry. However, the rapid decline in usage of organochlorine insecticides may not be ascribed solely to the recognition of risks associated with their use, but also to the increasing resistance of insect species to these and, indeed, to many other insecticides. These topics are discussed in the opening chapters of this volume and provide a revealing perspective in which developments in the struggle against pests must be viewed. In this volume discussions of some major groups of pest control chemicals have been included, as well as some closely related topics such as insect and plant growth regulators. The authors are distinguished by their contributions to research and, as the organizer of the symposum, I would like to thank them for their participation; I would also like to thank my associates in this review who have prefaced each section by a viii

brief introduction. The selection of topics may appear capricious, but in such a broad field there is no attempt to claim that such a symposium can present anything other than a few of the highlights. I would like to acknowledge assistance and cooperation of my colleagues in this enterprise: P. C. Kearney, G. K. Kohn, J. J. Menn, R. D . O'Brien, and S. K. Ries. My grateful thanks is also due to May Inscoe for her assistance in editing and preparing this volume. U.S. Department of Agriculture

JACK R. PLIMMER

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November 1976

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1 Chlorinated Insecticides: Retrospect and Prospect G. T. BROOKS

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Agricultural Research Council, Unit of Invertebrate Chemistry and Physiology, University of Sussex, Brighton, BN1 9QJ, England

The story of the discovery of the chlorinated hydrocarbon derived insecticides i s one of outstanding achievement which deserves due recognition. Indeed, the discovery within so few years of DDT, γ-HCH ( γ-BHC), the cyclodiene group and toxaphene, chlorinated insecticide types with distinct origins and synthetic principles, i s truly remarkable. The continuing value of DDT and some other chlorinated com­ pounds i n Third World crop protection and human health programmes i s widely recognised, whilst at the research l e v e l , chlorinated insecticides have already helped to elucidate the basic processes of insecticide metabolism which are a c r i t i c a l feature of insecti c i d a l action. Many questions remain outstanding i n regard to the mode of interaction of these compounds with insect nerve and i t s resistance to them; the answers to some of these questions may arise at any time as our knowledge progresses and may contribute to a better understanding of nerve function. For this Symposium on Pesticide Chemistry in the 20th Century, in the American Bicentennial year, it seemed appropriate to view this immense subject i n a h i s t o r i c a l context, leading up to the present day situation. Benzene Hexachloride In one sense, the story of the chlorinated insecticides begins i n 1774, since in that year the Swedish apothecary Karl Wilhelm Scheele discovered chlorine. Michael Faraday, who was born in 1791, first assisted Sir Humphry Davy and later succeeded him as Professor of Chemistry at the Royal Institution i n London. In the Philosophical Transactions of 1825 Faraday reported that benzene reacted with chlorine i n sunlight to give a "solid body" and dense, viscous f l u i d , which was undoubtedly the f i r s t sample of technical BHC. During the next 87 years several investigations established i t s constitution to be C^H^Cl, and showed that i t con­ tained a- and β-isomers and afforded tricnlorobenzenes when treated with a l k a l i . In 1912, the Belgian chemist Van der Linden 1

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discovered the δ- and Y- isomers. The l a t t e r comprises only ΙΟ­ Ι 5% o f the t e c h n i c a l m a t e r i a l and has come to be known as l i n d a n e , after i t s discoverer. Since Z e i d l e r had synthesised DDT i n a p u r e l y chemical cont­ ext i n l & 7 4 i t i s evident t h a t during much of the e x p l o s i v e European i n d u s t r i a l development o f the 1 9 t h Century, with i t s attendant disease t o l l and demand f o r i n c r e a s e d food production, two of the most remarkable pest c o n t r o l agents o f a l l time were already s i t t i n g on l a b o r a t o r y sheIves1 One hundred and seven years a f t e r F a r a d a y s f i r s t reported p r e p a r a t i o n o f BHC, Harry Bender o f the Great Western E l e c t r o Chemical Company i n C a l i f o r n i a , was l o o k i n g f o r new uses o f chlorine. He added benzene to l i q u i d c h l o r i n e i n a Dewar f l a s k i n the open a i r and n o t i c e d t h a t part o f the product which s p i l l e d on the ground ' a t t r a c t e d and k i l l e d f l i e s and bees'. Thus, although compounds such as p-dichlorobenzene had been used as fumigants s i n c e World War I and BHC i s s a i d to have been used i n smoke screens during t h a t war, Bender's o b s e r v a t i o n made i n 1932-3 and r e f e r r e d to only f l e e t i n g l y i n the l i t e r a t u r e ( 1 ) was the f i r s t i n d i c a t i o n t h a t t e c h n i c a l BHC had unusual i n s e c t i c i d a l p r o p e r t i e s . U n f o r t u n a t e l y , the d i s c o v e r y was l e s t because samples sent to Berkeley were r e c r y s t a l l i s e d there before being t e s t e d ; the Yisomer was r e j e c t e d with the mother l i q u o r s and no a c t i v i t y was found. The subsequent development of BHC was b e d e v i l l e d by t h i s a s s o c i a t i o n o f high a c t i v i t y only with the w i l l - o ' - t h e - w i s p Yisomer and i t i s evident t h a t only samples c o n t a i n i n g mainly the l e s s s o l u b l e a- and β- isomers, contaminated with small and v a r i a b l e amounts o f l i n d a n e , were t e s t e d between 1933 and 1942. In the e a r l y 1930s t e c h n i c a l BHC was made at the A l k a l i D i v i s i o n o f Imperial Chemical I n d u s t r i e s i n Widnes, as a pre­ cursor o f t r i c h l o r o b e n z e n e s u s e f u l as non-flammable d i e l e c t r i c s . Samples o f white, c r y s t a l l i n e BHC were screened r o u t i n e l y at ICI's J e a l o t t ' s H i l l l a b o r a t o r y and according to an account by Dr. C. C. Tanner ( 2 ) , were found 'not to be s t r i k i n g l y o v i c i d a l or a p h i c i d a l ' . Another r e p o r t ( 3 ) suggests t h a t i n 1937 the samples were found to be 'quite a c t i v e ' but the o b s e r v a t i o n was n e i t h e r followed up or p u b l i s h e d . When ICI's search f o r D e r r i s s u b s t i t u t e s began i n 1942, the samples o f BHC were again added to the screening l i s t because f a i r l y l a r g e amounts were available i n s t o r e from the d i e l e c t r i c days. They soon proved to be the only m a t e r i a l s with worthwhile a c t i v i t y a g a i n s t t u r n i p f l e a b e e t l e . F i n a l l y , i n the summer o f 1942, the pure a - and β-isomers, the only compounds b e l i e v e d at that time to be present i n the crude, c r y s t a l l i n e BHC, were i n d i v i d u a l l y t e s t e d and shown to be i n a c t i v e . The search f o r the a c t i v e component then began i n earnest and t h i s was shown to be the Y-isomer by Burrage, e a r l y i n 1943 (4)· In France, Dupire noted the i n s e c t i c i d a l a c t i v i t y of t e c h n i c a l BHC to c l o t h e s moths i n 1940-41 and the m a t e r i a l was subsequently evaluated against a g r i c u l t u r a l i n s e c t pests ( 5 ) . f

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DDT I n complete c o n t r a s t to the chance d i s c o v e r y o f l i n d a n e , M u l l e r ' s d i s c o v e r y o f the i n s e c t i c i d a l a c t i v i t y o f DDT i n 1939 was the c u l m i n a t i o n of a more or l e s s r a t i o n a l a p p l i c a t i o n o f expe r i e n c e and i n t u i t i o n i n the development and improvement o f e x i s t ing moth-proofing agents based on c h l o r i n a t e d benzenes* In e f f e c t , DDT evolved from water s o l u b l e moth-proofing agents v i a the benzene s o l u b l e moth-proofing agent Eulan BL o f I* G. F a r b e n i n d u s t r i e ( F i g u r e 1) and the s u l f o n e (B, F i g u r e 1) by an a p p l i c a t i o n o f the now c l a s s i c a l n o t i o n t h a t t o x i c a n t molecules c o n s i s t of 'toxophores' t h a t are c a r r i e d to the s i t e of a c t i o n by appropriate l i p o p h i l i c s t r u c t u r e s or f u n c t i o n a l groups. Eulan BL combines 3*4-dichlorobenzene, a l i p o p h i l i c r e s p i r a t o r y and contact poison, with the more p o l a r sulfonamide moiety. The sulfone (B, F i g u r e 1) i s a powerful stomach poison whereas i t s methaned e r i v e d analogue (C), l a c k i n g the e l e c t r o n e g a t i v e - SO^-group, has n e i t h e r good stomach poison nor good c o n t a c t a c t i v i t y . Hence, the i d e a arose t h a t f o r contact a c t i v i t y the moiety separating the benzene n u c l e i had to c o n t a i n a s t r o n g l y e l e c t r o n e g a t i v e , yet p r e f e r a b l y l i p o p h i l i c group and the trichloromethane group o f chloroform, a h i g h l y l i p o p h i l i c i n h a l a t i o n n a r c o t i c then became an obvious candidate. Thus, the DDT molecule must represent one o f the most remarkably s u c c e s s f u l examples o f a l l time of the f a b r i c a t i o n o f a new b i o a c t i v e molecule from simpler s t r u c t u r e s which have t h e i r own apparently d i s t i n c t b i o l o g i c a l e f f e c t s . ICI S c i e n t i s t s working on lindane r e c e i v e d the news o f the new Swiss i n s e c t i c i d e , but not i t s s t r u c t u r e , around Christmas time i n 1943· So s i m i l a r were the r e p o r t e d i n s e c t i c i d a l p r o p e r t i e s o f DDT to those o f lindane t h a t there was s p e c u l a t i o n as to whether the two compounds were v a r i a n t s of the same chemical. Cyclodiene I n s e c t i c i d e s The double event d e s c r i b e d above seems remarkable enough, but the d i s c o v e r y of the c y c l o d i e n e s and toxaphene, two f u r t h e r types o f broad spectrum c h l o r i n a t e d i n s e c t i c i d e s with d i s t i n c t o r i g i n s , was already imminent. The 'indene-derived' group. At the V e l s i c o l Chemical C o r p o r a t i o n i n Chicago i n 1943, Dr. J u l i u s Hyman was seeking new uses f o r the cyclopentadiene which was a by-product o f U.S. s y n t h e t i c rubber production and was already used by V e l s i c o l f o r the manufacture o f r e s i n s and varnishes by the D i e l s - A l d e r r e a c t i o n ( 6 ) . A l i t e r a t u r e search r e v e a l e d Straus's 1930 synthe s i s o f hexachlorocyclopentadiene (•hex ) and, s i n c e c h l o r i n a t e d dienes are f r e q u e n t l y r a t h e r i n e r t , Hyman was i n t e r e s t e d to determine i f 'hex would p a r t i c i p a t e i n the D i e l s - A l d e r r e a c t i o n , e i t h e r with i t s e l f or with cyclopentadiene. S u r p r i s i n g l y , 'hex r e a d i l y gave mono- and bis-adducts with 1

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Figure 2. Synthesis of Chlordene (A), the chlordane isomers (B and C), heptachlor (D), and heptachlor epoxide (8). Toxicities to house flies in μ&ι female (55) are underlined. /

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cyclopentadiene, and these were q u i c k l y t e s t e d f o r i n s e c t i c i d a l a c t i v i t y by P r o f e s s o r C. W. Kearns at the U n i v e r s i t y of I l l i n o i s - on the ground t h a t every new c h l o r i n a t e d hydrocarbon might be a p o t e n t i a l DDT (7). Great excitement attended the f i n d i n g that the mono-adduct (chlordene) was about one f o u r t h as t o x i c as DDT, which was newly appearing i n the U.S. Chlordene (A, F i g u r e 2) could be made more cheaply than DDT but was u n f o r t u n a t e l y too v o l a t i l e to compete with i t as a p e r s i s t e n t r e s i d u a l i n s e c t i c i d e . T h i s problem was overcome by c h l o r i n a t i n g the r e a c t i v e double bond to give chlordane (8) which a l s o was more v o l a t i l e than DDT but now s u f f i c i e n t l y p e r s i s t e n t f o r p r a c t i c a l purposes and s e v e r a l times more t o x i c than DDT to a number of i n s e c t s (housef l y LD50s i n ^ig/female u n d e r l i n e d i n F i g u r e 2)· Chlordane cont a i n s 40% or more of the c i s and t r a n s - products o f double bond c h l o r i n a t i o n (B and C, Figure 2 ) , about 10% o f heptachlor (D), and v a r i o u s other compounds ( 9 ) · I t has found many a p p l i c a t i o n s i n both p u b l i c h e a l t h programmes and a g r i c u l t u r e . R. Riemschneider o f the Free U n i v e r s i t y of B e r l i n was undoubtedly examining the r e a c t i o n s o f 'hex* i n 1945-46 and publ i s h e d on the i n s e c t i c i d a l a c t i o n o f chlordane e a r l y i n 1947 (10)· T h i s i s i n t e r e s t i n g i n view o f the communication d i f f i c u l t i e s o f the time and may be one example o f the f r e q u e n t l y observed spontaneous appearance of s i m i l a r s c i e n t i f i c d i s c o v e r i e s at nearly the same time i n d i f f e r e n t p a r t s of the world. 1

The 'naphthalene-derived group. Sometimes thus c a l l e d because of t h e i r s t r u c t u r a l o r i g i n s , the nevertheless nonaromatic compounds, a l d r i n , d i e l d r i n , i s o d r i n and e n d r i n arose from Hyman's d i s c o v e r y that cyclopentadiene r e a c t s with acetylene to give b i c y c l o [ 2 . 2 . 1 J hepta-2,5-diene (norbornadiene; A, Figure 3) as a s t a b l e product p r e v i o u s l y supposed incapable o f existence, I t was then l o g i c a l to t e s t i t s r e a c t i o n as a d i e n o p h i l e with •hex*. T h i s D i e l s - A l d e r r e a c t i o n occurs r e a d i l y and l e d to the f i r s t p r e p a r a t i o n o f a l d r i n e a r l y i n 1948 (HHDN; D, F i g u r e 3 ) . Attempts to reduce the v o l a t i l i t y o f a l d r i n without e l i m i n a t i n g i t s i n s e c t i c i d a l p r o p e r t i e s soon l e d to the d i s c o v e r y o f the corresponding epoxide, d i e l d r i n (HEOD; E, F i g u r e 3 ) , by Soloway ( 6 , 11). I n F i g u r e 3, h o u s e f l y LD50s i n ug/female are underlined. I f the d i e n o p h i l e (norbornadiene) i s c h l o r i n a t e d i n s t e a d , e i t h e r v i a the r e a c t i o n o f 'hex' with v i n y l c h l o r i d e followed by d e h y d r o c h l o r i n a t i o n , or d i r e c t l y with acetylene, to give 1,2,3«4, 7,7-hexachlorobicyclo[2.2.1 J] hepta-2,5-diene (hexachloronorbornadiene; B, F i g u r e 3 ) , t h i s compound r e a c t s with cyclopentadiene to give i s o d r i n (C; precursor o f the epoxide, endrin) having the opposite (endo-,endo-) stereochemistry to a l d r i n (and d i e l d r i n ) , r e s p e c t i v e l y (12). I s o d r i n has not found commercial use but e n d r i n has been widely used i n t r o p i c a l and s u b - t r o p i c a l a g r i c u l ture - to c o n t r o l c o t t o n pests, f o r example. The 'indene' and 'naphthalene' d e r i v e d compounds may be

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Figure 3.

Synthesis of isodrin (C), aldrin (D), and dieldrin (E) (11, 12). Housefly toxicities in ^g/female (55) are underlined.

Figure 4. Products (middle row) of camphene chlorination in the dark (15, 1β) and toxic compounds (bottom row) recently isohted from toxaphene (17,18)

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regarded as the core d i s c o v e r i e s of the c y c l o d i e n e s e r i e s , although another important and widely used c y c l o d i e n e , endosulfan, was d i s c o v e r e d by Dr. Heinz Frensch and h i s c o l l a b o r a t o r s at Farbwerke-Hoechst i n the mid 1950s ( 1 3 ) . Endosulfan i s a hydrol y s a b l e c y c l i c s u l f i t e e s t e r d e r i v e d i n d i r e c t l y from hex' and i s environmentally much l e s s p e r s i s t e n t than most other c y c l o d i e n e s . Another c y c l o d i e n e , isobenzan, had too great a mammalian t o x i c i t y to achieve p r a c t i c a l use. An obvious p o i n t of c o n t r a s t with the DDT or lindane s t o r i e s i s the number o f h i g h l y e f f e c t i v e i n s e c t i c i d e s d e r i v e d from •hex that have a c t u a l l y achieved commercial use. e

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Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch001

Toxaphene The dark c h l o r i n a t i o n of camphene was f i r s t r e p o r t e d i n 1919 by L a n g l o i s , who assigned c o r r e c t s t r u c t u r e s to two of the products. In 1944, the Russians Khanenia and Zhuravlev, seeking chemicals to c o n t r o l b o d y - l i c e , noted that the m i l d t o x i c i t y of terpenes contained i n t u r p e n t i n e was g r e a t l y enhanced by c h l o r i n a t i o n . A l s o , about t h i s time Dr. G. A. Buntin o f the Hercules Research Center l a b o r a t o r i e s i n Wilmington was aware of the e x i s t ence o f D D T and was conducting a s y n t h e t i c programme d i r e c t e d toward household i n s e c t c o n t r o l . The f i r s t sample of toxaphene was prepared at Hercules and found to be t o x i c t o h o u s e f l i e s i n March 1944. L a t e r that year, t e s t s by the USDA showed toxaphene to be t o x i c to a wide range o f c o t t o n i n s e c t s and p i l o t s c a l e p r e p a r a t i o n began at Wilmington i n September 1945 (14). Two independent r e p o r t s i n I965 ( 1 5 » 16) e s t a b l i s h e d the major products o f dark r e a c t i o n (middle row, F i g u r e 4) f i r s t i n v e s t i g a t e d by L a n g l o i s , but toxaphene i t s e l f i s a much more complex product r e s u l t i n g from photochemical c h l o r i n a t i o n o f camphene to a c h l o r i n e content o f 6 7 - 6 9 % , corresponding to an average formula ^ Q I Q Q According to recent r e p o r t s ( 1 7 , 1 8 ) , toxaphene c o n t a i n s at l e a s t 175 C - c h l o r i n a t e d hydrocarbons. A recently i s o l a t e d C l ^ compound (B, F i g u r e 4) and a mixture o f isomeric C l g compounds (A^ and A^) comprise 2 and 6% r e s p e c t i v e l y , of t h i s mixture ( 1 7 ) · These two i s o l a t e s are present i n r e l a t i v e l y l a r g e amounts compared with many other components and are considered t o c o n t r i b u t e s i g n i f i c a n t l y to the mammalian t o x i c i t y o f the comm e r c i a l product. Although these two i s o l a t e s are more t o x i c than the t e c h n i c a l mixture ( r e s p e c t i v e l y , 6x and l 4 x more t o x i c to mice and 2x and 4x more t o x i c to h o u s e f l i e s ) , they are l i k e l y to be biodegradable, so that a study o f t h e i r s t r u c t u r e s i n r e l a t i o n to those of other c h l o r i n a t e d p o l y c y c l i c i n s e c t i c i d e s i s of t h e o r e t ical interest. Toxaphene has been very widely used i n both a g r i c u l t u r e and p u b l i c h e a l t h programmes. Since i t s i n t r o d u c t i o n , one b i l l i o n l b have been a p p l i e d to crops and l i v e s t o c k f o r i n s e c t c o n t r o l . I t i s s t i l l used at the r a t e of 40 m i l l i o n l b annually, mostly combined with methyl p a r a t h i o n f o r treatment o f c o t t o n . I t was formc

H

C 1

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PESTICIDE CHEMISTRY IN THE 20TH CENTURY

8

e r l y combined with DDT f o r t h i s purpose and i n 1964, toxaphene and DDT together comprised about 4 6 % o f the t o t a l p e s t i c i d e s used i n the U.S. The c o t t o n market absorbed h a l f of the t o t a l i n s e c t i c i d e s used and accounted f o r 70% o f the DDT, 6 9 % of the toxaphene and 86% o f the endrin employed ( 1 9 ) · For comparison, the corn market absorbed 10% of the t o t a l i n s e c t i c i d e usage and accounted f o r 96% o f the a l d r i n and 8 4 % o f the heptachlor used, an i l l u s t r a t i o n of the d i f f e r e n t s p e c t r a o f crop p r o t e c t i o n u t i l i t y f o r the v a r i o u s c h l o r i n a t e d i n s e c t i c i d e s . The

R e c a l l i n g that parathion was developed as an i n s e c t i c i d e by a y e r i n 1944 and that the Geigy Company were developing the carbamate a n t i c h o l i n e s t e r a s e s f o r t h i s purpose i n the l a t e 1 9 4 0 s , we see t h a t the 1950s were entered with ( i n c l u d i n g toxaphene) no l e s s than four new c l a s s e s of c h l o r i n a t e d i n s e c t i c i d e s and two new c l a s s e s o f a n t i c h o l i n e s t e r a s e i n s e c t i c i d e s - a t r u l y unique situation. With t h i s array of i n s e c t i c i d a l compounds a v a i l a b l e and f o l l o w i n g the s p e c t a c u l a r wartime success of DDT, i t seemed that the t o t a l e l i m i n a t i o n of i n s e c t vectors of disease was at hand and that unheard of b e n e f i t s to a g r i c u l t u r e l a y ahead. Nevertheless, many o f the e c o l o g i c a l problems that might r e s u l t from the use of DDT and other p e r s i s t e n t compounds i n a g r i c u l t u r e were already recognised and the prospects f o r DDT i n a g r i c u l t u r e were viewed with some c a u t i o n i n 1944. However, i t i s doubtful whether the p o s s i b i l i t y o f i n s e c t r e s i s t a n c e to the new i n s e c t i c i d e s had been considered, so the appearance o f DDT-resistance i n Sweden and Denmark i n 1946, and subsequently i n other areas, was a cons i d e r a b l e shock to those engaged i n i n s e c t c o n t r o l . Control f a i l u r e s were f r e q u e n t l y b e l i e v e d to be due to f a u l t s i n the technology of DDT a p p l i c a t i o n r a t h e r than to changes i n the i n s e c t s themselves; a s i t u a t i o n which o f t e n l e d to e x t r a t r e a t ments with the t o x i c a n t and hence to greater s e l e c t i o n pressure f o r r e s i s t a n c e i n the i n s e c t populations. The onset o f DDT-resistance i n i t i a t e d the f i r s t i n v e s t i g a t i o n s i n what has come to be known as Insect Toxicology and the great value of r a d i o t r a c e r s f o r such work soon became apparent. The 1951 r e p o r t by Winteringham (20) o f the comparative metabolism of l , l , l - t r i c h l o r o - 2 , 2 - b i s ( p - C Brjphenyl)ethane( Br-DDT ) i n s u s c e p t i b l e (S-) and r e s i s t a n t (R-) h o u s e f l i e s must have been one of the e a r l i e s t a p p l i c a t i o n s o f t h i s technique to the metabolic f a t e o f an organic i n s e c t i c i d e i n i n s e c t s . Metabolites were separated on paper chromatograms which were then analysed r a d i o m e t r i c a l l y using s t r i p - s c a n n e r s designed and made i n the Slough laboratory. Enzymatic d e h y d r o c h l o r i n a t i o n proved to be l a r g e l y responsi b l e f o r DDT-resistance i n some i n s e c t s t r a i n s , as was demonstrated by the f a c t that DDT-analogues which i n h i b i t e d the enzyme i r i Q

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch001

Post-War Years

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch001

1.

BROOKS

Chlorinated

Insecticides

9

v i t r o and i n v i v o could synergise DDT i n such s t r a i n s ( 2 1 ) . T h i s observation generated a great i n t e r e s t i n s y n e r g i s t i c combinations* I n a d d i t i o n , the b e n z y l i c d e u t e r a t i o n o f DDT ( 2 2 , 23) suppressed d e h y d r o c h l o r i n a t i o n only i n c e r t a i n mosquitoes, whereas a s i n g l e <>-chlorine suppressed i t i n h o u s e f l i e s (24), thereby demonstrating i n t e r s p e c i f i c d i f f e r e n c e s i n the substrate speci f i c i t y o f the enzyme. Kearns and h i s c o l l e a g u e s concentrated the enzyme from R - h o u s e f l i e s i n 1954 and s t u d i e d i t e x t e n s i v e l y i i the l a t e 1950s ( 2 5 ) ; i t s n a t u r a l f u n c t i o n i s s t i l l unknown. I t i s not present i n s i g n i f i c a n t amounts i n DDT-S s t r a i n s o f housef l i e s , although some o f these c o n t a i n an enzyme with d i f f e r e n t substrate s p e c i f i c i t y . Resistance to the c y c l o d i e n e s was evident by t h i s time and was known to extend t o lindane and toxaphene but not to DDT. These c r o s s - r e s i s t a n c e patterns were s t u d i e d by J. R. Busvine a t the London School o f Hygiene. H i s p a r t l y d i e l d r i n r e s i s t a n t s t r a i n o f M. domestica v i c i n a from the Sudan became 1 0 0 0 - f o l d r e s i s t a n t when subjected to intense pressure with d i e l d r i n a t Slough. . i ! 9 5 7 I d e v i s e ^ the f i r s t s y n d e s e s o f £ C J i s o d r i n and L CJendrin ( 2 6 ) . £ c}aldrin and C c] d i e l d r i n were l a t e r made at the Radiochemical Centre a t Amersham, so i t was p o s s i b l e to compare the f a t e o f a l l these compounds i n S- and R- h o u s e f l i e s . The w e l l known e p o x i d a t i o n r e a c t i o n occurred e q u a l l y w e l l i n both s t r a i n s but there appeared to be no other s i g n i f i c a n t metabolism or any obvious d i f f e r e n c e s to account f o r the r e s i s t a n c e ( 2 7 ) * We now know t h a t a s i n g l e gene on chromosome IV i s r e s p o n s i b l e f o r d i e l d r i n r e s i s t a n c e i n h o u s e f l i e s . The mechanism i s s t i l l obscure, although recent work has shown t h a t h o u s e f l i e s do metabolise small amounts o f d i e l d r i n ( 2 8 ) . Before I 9 6 0 , there was a widespread b e l i e f that the c y c l o dienes were m e t a b o l i c a l l y i n e r t , apart from the epoxidation r e a c t i o n . By 1955» i t was appreciated that mammalian l i v e r conv e r t s c e r t a i n organophosphorus compounds i n t o a c t i v e a n t i c h o l i n e s t e r a s e s by o x i d a t i v e r e a c t i o n s and O'Brien ( 2 9 ) showed t h a t these conversions were e f f e c t e d by l i v e r microsomes f o r t i f i e d with NADPH. Drug metabolism s t u d i e s were about to be a c c e l e r ated by f u r t h e r important developments; the microsomal mixed f u n c t i o n oxidases (MFO) that are i n v o l v e d i n drug metabolism i n mammals were d e s c r i b e d i n 1 9 5 6 - 7 , and about the same time, c y t o chrome P 4 5 0 , the CO-binding pigment r e s p o n s i b l e f o r oxygen a c t i v a t i o n by these enzymes, was discovered i n mammalian l i v e r . A l i n k with c h l o r i n a t e d i n s e c t i c i d e (OC) metabolism i n i n s e c t s appeared between 1958 and i 9 6 0 when the b e n z y l i c hydroxyl a t i o n o f DDT was n o t i c e d by Japanese ( 3 0) and American i n s e c t t o x i c o l o g i s t s ; i n i 9 6 0 the American group showed t h a t i t r e s u l t e d from MFO a t t a c k ( 3 1 ) . A l s o i n i 9 6 0 , Sun and Johnson (32) showed that p y r e t h r i n s y n e r g i s t s such as benzodioxole d e r i v a t i v e s i n h i b i t e d the o x i d a t i v e d e t o x i c a t i o n o f i n s e c t i c i d e s and at l a s t solved the long-standing mystery o f p y r e t h r i n synergism by these I

n

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch001

10

PESTICIDE CHEMISTRY IN THE 20TH CENTURY

compounds i n i n s e c t s ; i t now seemed c e r t a i n t h a t they were MKO i n h i b i t o r s jln v i v o . At t h i s time I was i n t e r e s t e d i n the n a t u r a l t o l e r a n c e o f h o u s e f l i e s to s t r u c t u r a l analogues o f d i e l d r i n and, with Harrison. I soon showed t h a t whereas t o l e r a n c e t o c y c l o d i e n e s was o f t e n r e l a t e d to o x i d a t i v e d e t o x i c a t i o n and could be reduced or e l i m i n ­ ated by benzodioxole s y n e r g i s t s , d i e l d r i n - r e s i s t a n c e i n housef l i e s d i d not respond t o synergism and was apparently not a con­ sequence o f o x i d a t i v e d e t o x i c a t i o n ( 3 3 ) · Several l a b o r a t o r i e s ( f o r t h e i r subsequent reviews see 3 4 - 3 6 ) confirmed the importance of o x i d a t i v e b i o t r a n s f o r m a t i o n s i n i n s e c t s and i n 1 9 6 4 - 5 , a t Slough, J. W. Ray showed t h a t microsomal preparations from housef l i e s and other i n s e c t s contained cytochrome P450 ( 3 7 ) · Thus, the l i n k s between i n s e c t and mammalian biochemical pharmacology were f i n a l l y and f i r m l y e s t a b l i s h e d . Several i n v e s t i g a t i o n s ( 3 8 - 4 θ ) between i 9 6 0 and 1965 f i n a l l y d i s p e l l e d the myth o f d i e l d r i n s metabolic i n e r t n e s s i n mammals and s i n c e then numerous l a b o r a t o r i e s have shown t h a t c y c l o d i e n e s conform t o the e s t a b l i s h e d p r i n c i p l e s o f drug metabolism (41). Molecular s t r u c t u r e has a profound i n f l u e n c e on the exposure o f the non-chlorinated p o r t i o n s o f these molecules to enzymatic a t t a c k and the low p e r s i s t e n c e o f e n d r i n , as com­ pared to d i e l d r i n , i n mammalian t i s s u e s appears l a r g e l y due t o the stereochemical d i f f e r e n c e (42). The b i o t r a n s f o r m a t i o n s o f d i e l d r i n are summarised i n F i g u r e 5 · With the a p p l i c a t i o n o f e l e c t r o n - c a p t u r e (EC) and microcoulometric d e t e c t i o n to gas chromatograph e f f l u e n t s from i 9 6 0 , the e r a o f the measurement o f nothing i n everything had a r r i v e d and the environmental controversy was t r u l y on. I t was e a s i e r t o make an e f f e c t i v e EC d e t e c t o r than t o i n t e r p r e t the a n a l y t i c a l r e s u l t s c o r r e c t l y and many o f the i d e n t i f i c a t i o n s o f c h l o r i n a t e d i n s e c t i c i d e (OC) r e s i d u e s made i n the e a r l y 1960s a r e undoubt­ edly suspect, e s p e c i a l l y since i t was found i n 1966 that wide­ spread p o l y c h l o r o b i p h e n y l (PCB) contamination i n the bio-sphere can simulate OC i n gas chromatographic a n a l y s i s . In the United Kingdom i n 1960-1 we had the episodes o f b i r d poisoning due t o seed d r e s s i n g s t r e a t e d with d i e l d r i n and hepta­ c h l o r epoxide, and the controversy about the d e c l i n e o f the peregrine f a l c o n . Government and Industry then agreed t o reduce the use o f OCs and environmental l e v e l s f e l l i n the mid to l a t e 6 0 s , as i n d i c a t e d by the residue content o f human adipose t i s s u e , mutton f a t and shag's eggs. S i m i l a r r e s t r i c t i o n s i n c e n t r a l Europe have a l s o r e s u l t e d i n f a l l s i n r e s i d u e l e v e l s and there appears to have been a s i t u a t i o n o f d e c l i n e , or a t l e a s t stab­ i l i t y , i n the U.S. s i n c e about 1964. Extensive work i n the 1960s on the pharmacokinetics o f d i e l d r i n i n b i r d s and i n mammals, i n c l u d i n g man, together with e x i s t i n g data f o r DDT and other OCs, led Dr. John Robinson ( 4 3 ) to make the f o l l o w i n g p o s t u l a t e s : 1. OC l e v e l s i n d i f f e r e n t t i s s u e s are f u n c t i o n a l l y related. 1

1.

BROOKS 2.

3. 4·

Chlorinated

T i s s u e l e v e l s are f u n c t i o n a l l y r e l a t e d to the d a i l y intake o f OC. T i s s u e concentrations depend on the time of exposure. When exposure ceases t i s s u e l e v e l s d e c l i n e exponentially. COMPARTMENT II INERT STORAGE Q,

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch001

11

Insecticides

COMPARTMENT I ACTIVE POOL <3

7\-

DAILY INTAKE, RATE, R For

long term exposures,

^

k

ELIMINATION

(1-e e * ) , where

is

the

c o n c e n t r a t i o n i n the a c t i v e pool at lime t . Viewing the mammal as a simple, two compartment system of the mamillary type, the data imply that f o r a long term i n g e s t i o n at constant r a t e , plateau t i s s u e l e v e l s w i l l be a t t a i n e d ( Q ^ s — when t4oo) that are d i c t a t e d by the e q u i l i b r i u m between intake e and e l i m i n a t i o n . T h i s c o n c l u s i o n should be g e n e r a l l y a p p l i c a b l e and e x p l a i n s the f a l l i n residue l e v e l s observed when exposure i s reduced (66-70)· Besides t h e i r biochemistry and t o x i c o l o g y , the environmental chemistry of OCs has been e x t e n s i v e l y s t u d i e d ( 4 4 , 45)· The photochemistry of the c y c l o d i e n e s , f o r example, o f f e r s a f e a s t f o r the chemist ( 4 4 ) , though perhaps a headache f o r the r e s i d u e a n a l y s t and t o x i c o l o g i s t . The breakdown of terminal r e s i d u e s to simple molecules capable of e n t e r i n g the n a t u r a l organic c y c l e s depends u l t i m a t e l y on m i c r o b i a l a c t i v i t y and anaerobic d e c h l o r i n a t i o n seems an e s s e n t i a l p r e l i m i n a r y f o r OC d e s t r u c t i o n . Lindane i s r e l a t i v e l y non-persistent, e s p e c i a l l y under anaerobic c o n d i t i o n s , and although i t s more h i g h l y c h l o r i n a t e d r e s i d u e s may present the same problems as those o f polychlorophenols, the l e s s c h l o r i n a t e d r e s i d u e s should f o l l o w pathways s i m i l a r to those e s t a b l i s h e d f o r the m i c r o b i a l degradation of the c h l o r i n a t e d phenoxyalkanoic a c i d h e r b i c i d e s . Recent evidence ( 4 6 ) i n d i c a t e s that c e r t a i n microbes can d e c h l o r i n a t e DDT a n a e r o b i c a l l y , thereby making a v a i l a b l e intermediates which may undergo f u r t h e r aerobic attack, leading i n p r i n c i p l e to t o t a l degradation. The u l t i m a t e f a t e o f the hexachloronorbornene nucleus o f c y c l o d i e n e s i s s t i l l u n c e r t a i n and t h i s question continues to a t t r a c t a t t e n t i o n . f

Present Status of C h l o r i n a t e d

Insecticides

In 1 9 6 3 i the P r e s i d e n t ' s Advisory Committee on the Use P e s t i c i d e s recommended that the ' e l i m i n a t i o n of the use of

of

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch001

12

PESTICIDE CHEMISTRY IN THE 20TH CENTURY

p e r s i s t e n t i n s e c t i c i d e s should be the g o a l ' . The ensuing skirmi s h between the a d m i n i s t r a t i o n and the manufacturers has culminated i n the U.S. ban on the use of DDT from 1973 and the more recent ban on a l d r i n and d i e l d r i n . F u r t h e r , the f u t u r e o f chlordane and r e l a t e d compounds i s now u n c e r t a i n . C l e a r l y , the bans w i l l have s h a r p l y a c c e l e r a t e d the d e c l i n e i n home use already evident i n the 1960s and due p a r t l y to r e s i s t a n c e problems. I r o n i c a l l y , those pressures o f the l a s t 15 years or so have generated more i n f o r m a t i o n about the environmental t o x i c o l o g y of c h l o r i n a t e d i n s e c t i c i d e s than we may ever gain about other c l a s s e s o f p e s t i c i d e s or environmental contaminants. As a s i d e b e n e f i t , we now know t h a t some x e n o b i o t i c s may be t r a n s f e r r e d i n t o g l o b a l areas they were never intended to reach and we have developed the methodology needed to measure these low l e v e l contaminations. I t i s a l s o doubtful whether the extensive background contamination by PCB would have come to l i g h t so q u i c k l y without the widespread concern about OC. The annual g l o b a l use of DDT f o r disease v e c t o r c o n t r o l i s now running at about 66% (4o,000 tons) o f the I960 l e v e l and i s expected to remain constant f o r the next decade ( 4 7 ) · Major DDT r e s i s t a n c e e x i s t s i n about 1% o f the area t r e a t e d f o r m a l a r i a c o n t r o l and although a l i m i t e d number o f organophosphate and carbamate a l t e r n a t i v e s are a v a i l a b l e , t h e i r use i s so much more c o s t l y that t o t a l DDT replacement seems economically i m p o s s i b l e . Many of the l e s s prosperous c o u n t r i e s regard DDT as the most important l i f e - s a v e r known to man. Use o f the other OC i s more l i m i t e d and r e s i s t a n c e to them g e n e r a l l y more i n t r a c t a b l e when i t occurs. Outside the U.S. c h l o r i n a t e d i n s e c t i c i d e s have accounted f o r h a l f o f the i n s e c t i c i d e s used i n crop p r o t e c t i o n (e.g. vegetables, 46%; r i c e , 57%? other c e r e a l s , 85%; c o t t o n , 3 8 % , i n 1 9 6 6 ) . T h e i r major c o n t r i b u t i o n i s undeniable and w h i l s t there has now been some r e d u c t i o n i n p u b l i c h e a l t h uses, the crop p r o t e c t i o n uses i n poorer c o u n t r i e s seem l i k e l y to d e c l i n e only s l o w l y . As the r e s t o f the world s l i p s i n t o ever i n c r e a s i n g dependence on North America f o r i t s g r a i n s u p p l i e s ( 4 8 ) we cannot l i g h t l y abandon any of the w e l l proven means to maintain the food supply, p a r t i c u l a r l y i f the a l t e r n a t i v e s appear s a f e r o n l y because we know l e s s about themJ Nevertheless, n a t i o n s with s u f f i c i e n t resources to pioneer the f u t u r e must s u r e l y do so and the U.S. has long borne such responsibility. I f there i s doubt about the long term e f f e c t s o f chemicals i n the environment then i t i s c l e a r l y prudent to r e s t r i c t t h e i r use as f a r as p o s s i b l e . R e s t r i c t i o n s on use a l s o seem to be the only way to v e r i f y experimentally some of the s p e c u l a t i o n s about the long term behaviour o f e x i s t i n g r e s i d u e s . I f the reduced use o f OC i n the U.S. and other advanced c o u n t r i e s can compensate f o r the c o n t i n u i n g need f o r them elsewhere, then, h o p e f u l l y , the o v e r a l l degree o f environmental contamination can

1.

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be s t a b i l i s e d or even reduced without g r e a t l y u p s e t t i n g the s t a t u s quo regarding world crop p r o t e c t i o n .

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch001

What o f the future? The c h l o r i n a t e d i n s e c t i c i d e s w i l l continue to a t t r a c t a t t e n t i o n because many questions remain outstanding i n regard to t h e i r mode o f a c t i o n on l i v i n g organisms and because some o f the mechanisms o f i n s e c t r e s i s t a n c e to them are not y e t understood. There i s much evidence that poisoning by OC i s e s s e n t i a l l y r e v e r s i b l e and t h a t i n s e c t death a c t u a l l y r e s u l t s from p e r s i s t ­ ence i n v i v o , l e a d i n g to secondary e f f e c t s such as dehydration and s t a r v a t i o n . The i n t o x i c a t i o n of mammals i s a l s o r e v e r s i b l e but i n severe poisoning death may r e s u l t from r e s p i r a t o r y f a i l u r e , which does not occur i n i n s e c t s . T h i s r e v e r s i b i l i t y poses pro­ blems i f we wish to make the compounds more biodegradable f o r the purpose of greater environmental a c c e p t a b i l i t y . Increased b i o d e g r a d a b i l i t y i s l i k e l y to i n c r e a s e r e v e r s i b i l i t y and reduce the e f f i c i e n c y o f an i n s e c t i c i d e unless we can improve i t s i n t e r a c t i o n with the t a r g e t i t s e l f . During recent years, Holan i n A u s t r a l i a and Metcalf i n the U.S. have explored t h i s area f o r DDT, Nakajima i n Japan f o r lindane and the author f o r c y c l o d i e n e s . From an a n a l y s i s of the i n s e c t t o x i c i t i e s o f a s e r i e s o f DDT-analogues, Holan (49) concluded t h a t the optimal s i z e of the 'apex' o f DDT (the t r i c h l o r o m e t h y l group or equivalent) approximates to the diameter o f a hydrated sodiurn*and on t h i s b a s i s he modified some o l d e r DDT-analogues and a l s o devised some new biodegradable structures. In F i g u r e 6 , methylchlor (A) was once considered as a com­ m e r c i a l i n s e c t i c i d e and D A N P , reported i n 1953 (50)» was the f i r s t c h l o r i n e f r e e i s o t e r e of DDT. Biodegradable s t r u c t u r e s C, D and Ε were devised by Holan ( 4 9 , 51» 5 2 ) ; F and G by M e t c a l f s group ( 5 3 ) . These molecules are s u s c e p t i b l e to attack by MFO at the p o s i t i o n s arrowed, as w e l l as to enzymatic dehydrochlorina t i o n i n appropriate cases. Housefly t o x i c i t i e s (values r e l a t i v e to DDT underlined i n F i g u r e 6) are i n c r e a s e d by c o - a p p l i c a t i o n with i n h i b i t o r s such as the benzodioxole s y n e r g i s t s , which b l o c k MFO a t t a c k ir\ v i v o . I t i s w e l l known that such attack o x i d i s e s methyl to carboxyl and c l e a v e s simple alkoxy-groups. These are u s u a l l y d e t o x i c a t i o n r e a c t i o n s i n t a r g e t i n s e c t s but the r e s i d u a l molecules may yet be f a i r l y s t a b l e i n the environment. On the other hand, a molecule such as F (Figure 6) may undergo, besides MFO a t t a c k as arrowed, d e h y d r o c h l o r i n a t i o n and h y d r o l y s i s to yield two aromatic fragments which are more amenable to m i c r o b i a l a t t a c k than the parent. 1

Although lindane i s r e l a t i v e l y n o n - p e r s i s t e n t , some of i t s terminal r e s i d u e s may be h i g h l y c h l o r i n a t e d and i n i m i c a l to nont a r g e t organisms. Consequently, lindane analogues i n which c h l o r i n e i s r e p l a c e d by biodegradable groups should be advantageous from an environmental standpoint, as w e l l as being

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PESTICIDE CHEMISTRY IN THE 20TH CENTURY

Figure 5. Summary of the biotransformations of dieldrin. These involve hydroxyfotion, hydration, oxidative dechlorination, and reductive dechlorination (39,42, 65).

Figure 6. Biodegradable analogues of DDT (49-53). Arrows indicate points of attack by microsomal oxidases. Housefly toxicities relative to DDT (1.0) are underlined.

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of t h e o r e t i c a l i n t e r e s t * The Kyoto group r e c e n t l y explored the mode o f a c t i o n o f lindane r a t h e r thoroughly and made a number of a c t i v e analogues with the same s t e r i c c o n f i g u r a t i o n as lindane (54) · In F i g u r e 7 the mosquito t o x i c i t i e s of these analogues show a decreasing trend from top l e f t to bottom r i g h t of the s e r i e s shown* However, the a l k y l - , alkoxy- and a l k y l t h i o - d e r i v a t i v e s are s i m i l a r to lindane i n t h e i r t o x i c i t i e s to mosquitoes, h o u s e f l i e s and the German cockroach* Synergism by the MFO i n h i b i t o r p i p e r o n y l butoxide, e s p e c i a l l y against h o u s e f l i e s , i n d i c a t e s that these groups are s i t e s of o x i d a t i v e a t t a c k iri v i v o * These r e s u l t s show that provided the aaaeee c o n f i g u r a t i o n of lindane i s r e t a i n e d , c e r t a i n biodegradable groups of s i m i l a r s i z e may r e p l a c e c h l o r i n e . The hexamethoxy analogue has a low t o x i c i t y , even i n the presence o f p i p e r o n y l butoxide, so t h a t the replacement process has l i m i t s . The low t o x i c i t y o f t h i s l i p o p h i l i c d e r i v a t i v e of mucoinositol (aaaeee) i s o f i n t e r e s t i n r e l a t i o n to the e a r l y theory that lindane i s an antagonist of i n o s i t o l i n v i v o ( 4 ) · In the mid-1960s we showed f i r s t l y that the n a t u r a l tolerance of h o u s e f l i e s to c y c l o d i e n e s r e s u l t e d mainly from o x i d a t i v e d e t o x i c a t i o n ( 3 3 i 5 5 ) and secondly that another enzyme system, epoxide hydrase, converted c e r t a i n d i e l d r i n analogues i n t o the corresponding t r a n s - d i o l s , ( 5 6 , 5 7 ) · I n t e r s p e c i f i c d i f f e r e n c e s i n a b i l i t y to attack enzymatically the u n c h l o r i n a t e d r i n g systems of v a r i o u s analogues, e i t h e r o x i d a t i v e l y and/or h y d r a t i v e l y ( i f appropriate) can confer s e l e c t i v e t o x i c i t y between i n s e c t s p e c i e s and a l s o between i n s e c t s and mammals ( 5 8 ) * I s i t p o s s i b l e that b i o d e g r a d a b i l i t y of t h i s s o r t can be combined with a r e d u c t i o n i n c h l o r i n e content without l o s s i n toxicity? Information i n the l i t e r a t u r e suggests that t h i s might be the case and I have r e c e n t l y explored t h i s p o s s i b i l i t y . A l i t t l e background i s necessary at t h i s p o i n t . More than 20 years ago, Busvine (59) drew a t t e n t i o n to the c r o s s - r e s i s t a n c e between lindane and the c y c l o d i e n e s and pointed out that these molecules had i n common a c e r t a i n pentagonal arrangement of c h l o r i n e atoms. Following t h i s i n i t i a l observation, i t was n o t i c e d ( 6 0 , 6 l ) that the replacement of the v i n y l i c c h l o r i n e s of a l d r i n and d i e l d r i n by hydrogen increased t h e i r t o x i c i t i e s f o u r - f o l d and that f o r a l d r i n , the bridge c h l o r i n e atom a n t i - to the c h l o r i n a t e d double bond appeared to be more important f o r t o x i c i t y than the sync h l o r i n e atom ( 6 l ) . A l s o , an a l d r i n analogue c o n t a i n i n g only the 1 and 4 - c h l o r i n e s was h i g h l y and s p e c i f i c a l l y t o x i c to the German cockroach ( 6 l ) · Soloway ( 6 l ) suggested that the c y c l o d i e n e s and lindane have i n common two e l e c t r o n e g a t i v e centres separated by a s i m i l a r d i s t a n c e and pointed out the s i m i l a r i t y between the ' p r o f i l e s of these molecules viewed perpendicular to t h e i r plane of symmetry. I f one f u r t h e r regards the h i g h l y e f f e c t i v e and r a p i d l y a c t i n g lindane as a b e t t e r f i t to the same t a r g e t that i s a f f e c t e d by d i e l d r i n , then the two v i n y l i c c h l o r i n e s and the syn-Cl of the 1

16

PESTICIDE CHEMISTRY IN THE 20TH CENTURY

ALPHA PAIR AAEEEE

BETA

ΕΕΕΕΕΕ

ANALOGUES 3 Br 3,6di-Br 3SMe 3 OMe 1 Me 1 F

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch001

GAMMA AAAEEE

1,2 F, Br 1 OMe 1 Br 1,4-di-Me 1,2 di Br Hexa OMe

Figure 7. Conformations of the BHC (HCH) isomers and recent ana­ logues of the aaaeee (lindane) structure, some of which have additional biodegradable groups (54)

ΦΦ·ΕΦ>ίΦ £0 DIELDRIN

JXADIELDRIN

ODA

HCE

CI Dieldrin M

l

M

2

Analogs

:

S

A

Blowfly

LD 5 0 ; /

DIELDRIN

CI

Cl

Cl

Cl

0.017

a

,

C

MD

Η

Cl

Cl

Cl

0.022

a

'

b

SD

Cl

Cl

H

Cl

0.046 »

d

AD

b

Cl

Cl

Cl

H

1.047

BD

H

H

Cl

Cl

0.0049

MSD

H

Cl

H

Cl

0.10

SBD

H

H

H

Cl

0.020

ABD

H

H

Cl

H

0.42

e

d

Figure 8. Planar structure of dieldrin and partial structures of some dieldrin analogs (each containing six chlorine atoms) referred to in the text. Table below gives toxicities for dechlorinated derivatives of dieldrin (see key in figure) to adult female blowflies, Calliphora erythrocephala. Similar superscripts indicate significant difference at 95% probability level (63).

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d i e l d r i n bridge appear superfluous as f a r as molecular bulk i s concerned ( 6 2 ) · Now although replacement of c h l o r i n e by hydrogen may i n c r e a s e metabolic p o s s i b i l i t i e s and a l s o a l t e r e l e c t r o s t a t i c i n t e r a c t i o n s with the t a r g e t , these deductions from models appeared to accord with the l i m i t e d t o x i c i t y data a v a i l a b l e . The above i n f o r m a t i o n suggested t h a t , f o r d i e l d r i n at l e a s t , three s p e c i f i c c h l o r i n e atoms might be r e p l a c e d without l o s s i n t o x i c i t y (62) and confirmatory t o x i c i t y data f o r b l o w f l i e s (C. erythrocephala) are shown i n F i g u r e 8 . I n the molecule SBD, the r e d u c t i o n i n t o x i c i t y e f f e c t e d by replacement o f the s y n - c h l o r i n e o f d i e l d r i n to give SD appears to be o f f s e t by an i n c r e a s e (compare BD) e f f e c t e d by f u r t h e r replacement of the v i n y l i c c h l o r i n e s , so that SBD i s s i m i l a r to dieldrin in toxicity. I n c o n t r a s t , AD and ABD, which r e t a i n the syn-chlorine« are poor t o x i c a n t s . In t h i s s e r i e s there was no a p p r e c i a b l e synergism with the MFO i n h i b i t o r sesamex, i n d i c a t i n g t h a t when i n c r e a s e d LD50s were seen, these were not the r e s u l t o f enhanced MFO a t t a c k consequent upon the p r o g r e s s i v e replacement of c h l o r i n e . The C l ^ - d i e l d r i n analogues ODA and HCE are biodegradable due to o x i d a t i v e and/or h y d r a t i v e a t t a c k on t h e i r u n c h l o r i n a t e d r i n g s shown i n F i g u r e 8 . Can c h l o r i n e be r e p l a c e d by hydrogen i n such analogues without s e r i o u s l o s s , or perhaps even with an i n c r e a s e i n acute i n s e c t t o x i c i t y ? The products, having l o s t 1 to 3 c h l o r i n e atoms, should be more v u l n e r a b l e to enzymatic detoxication i n the t i s s u e s of higher animals and t h e i r t e r m i n a l r e s i d u e s more amenable to b a c t e r i a l degradation. The r e s u l t s f o r c e r t a i n dec h l o r i n a t e d analogues of e n d r i n , o x a d i e l d r i n , ODA and HCE are presented elsewhere (63) and p r e l i m i n a r y data (unpublished) are a v a i l a b l e f o r d e r i v a t i v e s o f endosulfan, isobenzan and alodan. T h i s y e t incomplete study shows t h a t i n a l l s e r i e s f o r which i n f o r m a t i o n i s a v a i l a b l e , the bridge a n t i - C l ( A ) i s indeed more important than the syn-C1 (s) f o r t o x i c i t y , but replacement o f the v i n y l i c c h l o r i n e s does not n e c e s s a r i l y confer the t o x i c i t y i n c r e a s e found i n the d i e l d r i n s e r i e s . The resemblance between lindane and the c y c l o d i e n e s t r u c t u r e i s p a r t i c u l a r l y s t r i k i n g i f one compares models of lindane and the photoisomer of the molecule SD (Figure 8 ) , i n which the S - c h l o r i n e i s r e p l a c e d by hydrogen and the usual double bond i s absent. There i s a l s o some s i m i l a r i t y , not very obvious from two dimensional s t r u c t u r e s , between models o f these molecules and of the t o x i c components (Figure 4;A,B) i s o l a t e d from toxaphene by Casida's group ( l j ) . T h i s i s to be expected from i n s e c t c r o s s r e s i s t a n c e p a t t e r n s and s i m i l a r i t i e s i n the poisoning syndrome produced by the three types of compound. For cyclohexane d e r i v a t i v e s , c o n v u l s i v e a c t i v i t y i s a s s o c i a t e d , apparently s p e c i f i c a l l y , with a p a r t i c u l a r molecular topography t h a t i s only achieved with the aaaeee arrangement o f substituents. However, the norbornene and camphene carbon skeletons apparently permit the attainment of a s i m i l a r topography

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PESTICIDE CHEMISTRY IN THE 20TH CENTURY

w h i l s t allowing a greater molecular v a r i e t y and hence a l a r g e r number o f t o x i c products. With the c y c l o d i e n e s i n p a r t i c u l a r , greater s t r u c t u r a l v a r i a t i o n i s p o s s i b l e i n the non-chlorinated p o r t i o n o f the molecules and t h i s has r e s u l t e d i n a number o f commercially v i a b l e a l t e r n a t i v e s with d i f f e r e n t uses. I t i s con­ c e i v a b l e that other carbon skeletons may be used to a t t a i n the same end and Mirex, f o r example, i s d e r i v e d from the s p i n d l e shaped f u s i o n product o f two cyclopentadiene n u c l e i . In c o n c l u s i o n , our knowledge o f i n t e r s p e c i f i c d i f f e r e n c e s i n drug metabolism i s already being a p p l i e d to the question o f greater environmental a c c e p t a b i l i t y o f c h l o r i n a t e d as w e l l as other types o f i n s e c t i c i d e s . For example, the simple replacement of p - c h l o r i n e s by p-ethoxy-groups i n the w e l l known DDT-relative P r o l a n g i v e s the biodegradable compound D (Figure 6 ) , which has low mammalian t o x i c i t y and has been shown i n extensive f i e l d t r i a l s to be e f f e c t i v e against a wide range o f i n s e c t s p e c i e s ( 6 4 1 At the more fundamental l e v e l , mode o f a c t i o n s t u d i e s with c h l o r i n a t e d i n s e c t i c i d e s may y e t lead to novel i n s e c t i c i d a l compounds. We must accept that no device o f man w i l l ever be p e r f e c t . W h i l s t remaining watchful f o r the i n e v i t a b l e p i t f a l l s , we should never f o r g e t the many p o s i t i v e achievements already recorded i n the f i e l d o f i n s e c t c o n t r o l by chemicals.

Literature Cited 1. 2. 3. 4. 5. 6. 7. 8. 9· 10. 11. 12. 13. 14. 15· 16. 17.

Bender, H. U.S. Patent 2,010,841 (1935). Cited in Brooks G.T. 'Chlorinated Insecticides' Vol. I, p. 186, CRC Press, Cleveland, 1974. Holmes, E. Agr. Chem. (l951) 6 (12), 31. Slade, R.E. Chem. Ind. (Lond.) (1945) 64, 3l4. Dupire Α., and Raucourt, M. C.R. Acad. Agric. Fr. (1943) 29, 470. Hyman, J. Private communication. Kearns, C.W., Ingle, L., and Metcalf, R.L. J. Econ. Entomol. (1945) 38, 661. Hyman, J. Brit, patent 6l8,432 (1949). Gab, S., Parlar, Η., Cochrane, W.P., Fitzky, H.G., Wendisch, D., and Korte, F. Justus Liebigs Ann. Chem. (1976) 1. Riemschneider, R. World Rev. Pest Control (1963) 2, 29. Lidov, R.E., and Soloway, S.B. Brit, patent 692,547 (1953). Bluestone, H. U.S. Patent 2,676,132 (1954). Frensch, H. Med. Chem. (1957) 6, 556. Buntin, G.A. Private communication. Jennings, B.H., and Herschbach, G.B. J. Org. Chem. (1965) 30, 3902. Richey, H.G.Jr., Grant J.E., Garbacik, T . J . , and Dull, D.L. J. Org. Chem. (1965) 30, 3909. Khalifa, S., Mon, T.R., Engel, J.L., and Casida, J.E. J. Agric. Food Chem. (1974) 22, 653.

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18. 19·

20. 21. 22.

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23. 24. 25·

26. 27. 28. 29. 30. 31· 32. 33· 34. 35·

36. 37· 38. 39. 40. 41. 42.

Chlorinated Insecticides

19

Nelson, J.O., and Matsumura, F. J. A g r i c . Food Chem. ( 1 9 7 5 ) 23, 984. Department of H e a l t h , Education and Welfare, 'Report of the S e c r e t a r y ' s Commission on P e s t i c i d e s and t h e i r R e l a t i o n ­ s h i p to Environmental H e a l t h , P a r t s I and I I , p. 47, U . S . Govt. P r i n t Off., Washington DC, 1969. Winteringham, F.P.W., Loveday, P.M., and H a r r i s o n , A. Nature (Lond.) (1951) 167, 106. M o o r e f i e l d , H.H., and Kearns, C.W. J. Econ. Entomol. (1955) 4 8 , 403. Dachauer, A.C., Cocheo, B., Solomon, M.G., and Hennessy, D.J. J. A g r i c . Food Chem. (1963) 11, 47. Barker, R.J., J. E c o n . Entomol. (1960)53,35. Hennessey, D.J., F r a n t a n t o n i , J., H a r t i g a n , J., M o o r e f i e l d , H . H . , and Weiden, M.H.J. Nature (Lond.) (1961) 190, 341. L i p k e , Η . , and Kearns, C.W. 'Advances i n Pest C o n t r o l Research' V o l . 3, p. 253. M e t c a l f , R.L. E d . , I n t e r s c i e n c e New York, 1960. Brooke, G.T. J. Chem. Soc. (1958) 3693. Brooks, G.T. Nature (Lond.) (1960) 186, 96. S e l l e r s , L . G . and G u t h r i e , F.E. J. Econ. Entomol. (1972) 65, 378. O ' B r i e n , R.D. Canad. J. Biochem. (1955) 34, 1131. Tsukamoto, M. Botyu-Kagaku (1959) 24, 151. Agosin, M., M i c h a e l i , R., Miskus, S., Nagasawa, S., and Hoskins, W.M. J. E c o n . Entomol. (1961) 54, 340. Sun, Y.P., and Johnson, E.R. J. A g r i c . Food Chem. (1960) 8, 2 6 l . Brooks, G.T., and H a r r i s o n , A. J. Insect P h y s i o l . (1964) 10, 633. Tsukamoto, Μ . , and C a s i d a , J.E. Nature (Lond.) (1967) 213, 49. Dahm, P.Α., and Nakatsugawa, T., i n 'Enzymatic Oxidations of T o x i c a n t s ' p. 89, Hodgson, E. Ed., North C a r o l i n a State U n i v e r s i t y , R a l e i g h , 1963. Hook, G.E.R., Jordon, T.W., and Smith, J.N., i n 'Enzymatic O x i d a t i o n of T o x i c a n t s ' p. 27, Hodgson, E. Ed., North C a r o l i n a State U n i v e r s i t y , R a l e i g h , 1968. Ray, J.W., i n 'Pest I n f e s t a t i o n Research 1965, The Report of the Pest I n f e s t a t i o n L a b o r a t o r y ' , p. 59, A g r i c u l t u r a l Research C o u n c i l , London, 1965. Heath, D.F., and Vandekar, M. B r . J. Ind. Med. (1964) 211, 269. K o r t e , F., and A r e n t , H. L i f e S c i . (Oxford) (1965) 4, 2017. Cueto, C., and Hayes, W . J . J r . J. A g r i c . Food Chem. (1962) 10, 366. Brooks, G.T. i n ' P e s t i c i d e Terminal Residues (IUPAC)' p . 111, T a h o r i , A.S. Ed., Butterworths, London, 1971. Bedford, C.T., and Hutson, D.H. Chem. Ind. (London) (1976) 440.

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20

PESTICIDE CHEMISTRY IN THE 20TH CENTURY

43. Robinson, J., and Roberts, M. in 'Society of Chemical Industry Monograph No. 29' p. 106, SCI, London, 1968. 44. Rosen, J.D. in 'Environmental Quality and Safety' Vol. 1, p. 85, Coulston, F., and Korte, F. Eds., Thieme, Stuttgart, 1972. 45. Lu, Po-Yung, Metcalf, R.L., Hirwe, A.S., and Williams, J.W. J. Agric. Food Chem. (1975) 23, 967. 46. Pfaender, F.K., and Alexander, M. J. Agric. Food Chem. (1972) 20, 842. 47· Wright, J.W., and Stiles, A.R. in 'Pesticides', 'Environmental Quality and Safety', Suppl. Vol. III, p. 625, Coulston, F., and Korte, F., Eds., Thieme, Stuttgart, 1975. 48. Brown, L.R. Science (1975) 190, 1053. 49. Holan, G. Nature (London) (1969) 221, 1025. 50. Rogers, E.F., Brown, H.D., Rasmussen, I.M., and Heal, R.E. J. Amer. Chem. Soc. (1953) 75, 2991. 51. Holan, G. Nature (London) (l97l) 232, 644. 52. Holan, G. Bull. W.H.O. (1971) 44, 355. 53· Hirwe, A.S., Metcalf, R.L., and Kapoor, I.P. J. Agric. Food Chem. (1972) 20, 818. 54. Nakajima, M., Fujita, T., Kurihara, N., Sanemitsu, Y., Uchida, Μ., and Kiso, M . in 'Pesticides', 'Environmental Quality and Safety', Suppl. Vol. III, p. 370, Coulston, F., and Korte, F., Eds., Thieme, Stuttgart, 1975. 55· Brooks, G.T., Harrison, A. Biochem. Pharmacol. (1964) 13, 827. 56. Brooks, G.T. Wld. Review Pest Control (1966) 5, 62. 57· Brooks, G.T., Harrison, Α., and Lewis, S.E. Biochem. Pharmacol. (1970) 19, 255. 58. Brooks, G.T. in 'Environmental Quality and Safety', Vol. 1. p. 159, Coulston, F., and Korte, F., Eds., Academic, New York, 1972. 59. Busvine, J.R. Nature (Lond.) (1954) 174, 783. 60. Busvine, J.R. Bull. Entomol. Res. (1964) 55, 271. 61. Soloway, S.B. Adv. in Pest Control Res. (1965) 6, 85. 62. Brooks, G.T. in 'Drug Design', Vol. 4, p. 379, Ariens, E.J., Ed., Academic, New York, 1973. 63. Brooks, G.T. Proc. 8th Br. Insect Fungic. Conf. (1975) 38l. 64. Morton, T.C., Holan, G., and Virgona, C.T.F. Pestic. Biochem. Physiol. (1976) 6, 209. 65. Lay, J.P., Veisgerber, I., and Klein, W. Pestic. Biochem. Physiol. (1975) 5, 226. 66. Abbott, D.C., Collins, G.B., and Goulding, R. Brit. Med. J. (1972) 553. 67. Deichmann, W.B. Arch. Toxicol. (1972) 29, 1. 68. Cieleszky, V., and Soós, K. in 'Pesticides', Environmental Quality and Safety', Suppl. Vol. III, p. 199, Coulston, F., and Korte, F., Eds., Thieme, Stuttgart, 1975. 69· Aizicovici, H., Cocisiu, M., Nistor, C., and Unterman, W.H. Ibid, p.852. p.189. 70. Adamovic, V.M., Burke, J.Α., Sokić, Β., and Petrović, O.,Ibid/

2 The Progression of Resistance Mechanisms Developed against Insecticides A. W. A. B R O W N

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch002

Department of Entomology, Michigan State University, East Lansing, Mich. 48824

As the f i n a l item i n the symposium on pesticide chemistry i n this century, the need was f e l t for a review of outstanding events i n the insecticide resistance field during t h i s period, along with a projection of expectations during its f i n a l 25 years. This paper, however, will describe progressions rather than events, since resistance has been a steadily developing problem; t h i s pro­ gression w i l l be described i n d e t a i l , although the Forward Look will be pretty sketchy. Starting i n 1908 i n the orchards of the Pacific northwest, the cases of resistance before World War II and the era of the synthetic organics involved the HCN used against scale insects on c i t r u s , the arsenicals used against orchard c a t e r p i l l a r s and cat­ tle t i c k s , and tartar emetic applied against the t i n y insect pests called t h r i p s ; as now, many instances originated i n C a l i f o r n i a (Table I ) . The resistance mechanisms were investigated i n two of Table I.

Development of Insecticide-Resistances,

San Jose Scale Black Scale California Red Scale C i t r i c o l a Scale Codling Moth Peach Twig Borer Cattle Tick Blue Tick Citrus Thrips Gladiolus Thrips Two-spotted Mite Walnut Husk Fly

Lime-sulfur HCN HCN HCN Pb Arsenate Pb Arsenate Na Arsenite Na Arsenite Tartar Emetic Tartar Emetic Selenium Cryolite

1908-44.

Wash. State California California California Colorado California Argentina S. Africa California California Eastern US California

08 '12 ! 13 1 25 ! 28 •44 •35 f 38 f 39 f 43 ! 43 f 43

!

the cases: — the arsenic-resistant codling-moth larvae were found to be more resistant to starvation and desiccation, and thus had a longer period of effective locomotion to find an unsprayed spot on the skin of the apple (1); the cyanide-resistant C a l i f o r n i a red 21

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch002

22

PESTICIDE CHEMISTRY IN THE 20TH CENTURY

s c a l e had a t i s s u e - r e s p i r a t o r y e l e c t r o n - t r a n s p o r t s y s t e m l e s s de­ p e n d e n t on c y t o c h r o m e o x i d a s e ( 2 ) , and t h e c h a r a c t e r was f o u n d t o be i n h e r i t e d as i f i t was due t o a s i n g l e s e x - l i n k e d gene. The S w i s s p r o d u c t DDT was i n t r o d u c e d f o r h o u s e f l y c o n t r o l i n n e u t r a l c o u n t r i e s i n 1944, and a l r e a d y by 1946 r e s i s t a n c e had de­ v e l o p e d i n n o r t h e r n Sweden ( o f a l l u n l i k e l y p l a c e s ) . When h o u s e ­ f l y r e s i s t a n c e a p p e a r e d n e a r Rome, I t a l y i n 1947, P r o f e s s o r M i s s i r o l i c o n s i d e r e d t h a t i t was a d i f f e r e n t s u b s p e c i e s w h i c h he named Musca domestica tiberina a t t h e v e r y same t i m e t h a t W i l s o n and L i n d q u i s t i n t h e USDA O r l a n d o l a b o r a t o r y w e r e p r o d u c i n g a r e ­ s i s t a n t s t r a i n f r o m a s u s c e p t i b l e one by l a b o r a t o r y s e l e c t i o n . By 1952 D D T - r e s i s t a n c e had b e e n d e v e l o p e d i n p o p u l a t i o n s o f i m p o r ­ t a n t p e s t s o f a p p l e , c a b b a g e , p o t a t o e s , t o m a t o e s and g r a p e s , b e s i d e s t h e body l o u s e , t h e b e d b u g , two s p e c i e s o f f l e a s , and s e v e r a l species o f mosquitoes (Table I I ) . Table I I . Cabbage Worm Cabbage L o o p e r C o d l i n g Moth Apple PIant-bug Potato Beetle Potato Fleabeetle Diamondback Moth Tomato Hornworm Grape L e a f h o p p e r

D e v e l o p m e n t o f D D T - R e s i s t a n c e , 1946-52. Wis. N.Y. Ohio Wash. N.Y. Ind. Java Fla. Cal.

House F l y Body L o u s e Bed Bug Human F l e a Dog F l e a House M o s q u i t o Salt-marsh Mosquitoes I r r i g a t i o n - w a t e r Mosquitoes E n c e p h a l i t i s Mosquito

Sweden Korea Hawaii Peru Ga. Italy Fla. Cal. Cal.

The mechanism o f r e s i s t a n c e t o DDT i n t h e h o u s e f l y was a t f i r s t t h o u g h t t o be due t o r e d u c e d p e n e t r a t i o n t h r o u g h t h e c u t i c l e , the Swedish r e s i s t a n t f l i e s having a t h i c k e r t a r s a l integument t h a n n o r m a l l a b o r a t o r y s t r a i n s ( 3 ) . I n t e r s t r a i n d i f f e r e n c e s were f o u n d i n t h e t i t e r s o f c y t o c h r o m e o x i d a s e and c h o l i n e s t e r a s e , b u t t h e y b o r e no c o r r e l a t i o n w i t h t h e r e s i s t a n c e . One c h a r a c t e r i s t i c d i d , and t h a t was t h e d e t o x i c a t i v e d e h y d r o c h l o r i n a t i o n t o t h e noni n s e c t i c i d a l m e t a b o l i t e DDE ( F i g . 1 ) ; and t h e enzyme r e s p o n s i b l e , D D T - d e h y d r o c h l o r i n a s e , w h i c h depended on g l u t a t h i o n e f o r a c t i v a ­ t i o n , was i s o l a t e d f r o m r e s i s t a n t s t r a i n s ( 4 ) . A s e c o n d mechanism due t o n e r v e i n s e n s i t i v i t y t o DDT was d i s c o v e r e d i n s e v e r a l h o u s e ­ f l y s t r a i n s ( 5 ) . An a d d i t i o n a l mechanism o f D D T - r e s i s t a n c e f o u n d i n D a n i s h and C a l i f o r n i a n s t r a i n s s e l e c t e d w i t h OP compounds was due t o o x i d a t i o n , w h i c h c o u l d be p u t i n t o e v i d e n c e by t h e a d d i t i o n o f NADH t o m i c r o s o m a l p r e p a r a t i o n s in vitro, o r by a d d i n g t h e mfoi n h i b i t o r sesamex as a s y n e r g i s t in vivo ( 6 ) . The c y c l o d i e n e g r o u p o f o r g a n o c h l o r i n e s was i n t r o d u c e d i n 1948, s t a r t i n g w i t h c h l o r d a n e , t h e n a l d r i n , d i e l d r i n , e n d r i n and t o x a p h e n e , and t h e n h e p t a c h l o r ; BHC was a l r e a d y a v a i l a b l e a t t h e c l o s e o f t h e war. The e x p e r i e n c e w i t h h o u s e f l y c o n t r o l i n t h e M e d i t e r r a n e a n c o u n t r i e s was t h a t D D T - r e s i s t a n c e came i n 2 y e a r s , and t h e s u b s t i t u t i o n o f BHC was f o l l o w e d by B H C - r e s i s t a n c e a y e a r

2.

BROWN

Resistance

Mechanisms

against

23

Insecticides

l a t e r ; t h e same t h i n g happened t o t h e c y c l o d i e n e s c h l o r d a n e o r d i e l d r i n , a n d c r o s s - r e s i s t a n c e between BHC a n d t h e c y c l o d i e n e was v i r t u a l l y complete. W i t h i n 10 y e a r s o f t h e i n t r o d u c t i o n o f c y c l o ­ d i e n e s i n t o a g r i c u l t u r e i n 1949, 8 i m p o r t a n t c o t t o n p e s t s h a d gone d e c i s i v e l y r e s i s t a n t t o them, t h e b o l l w e e v i l b e i n g among t h e l a s t t o go ( T a b l e I I I ) . T h i s type o f r e s i s t a n c e developed p a r t i c u l a r l y f a s t i n f l i e s and mosquitoes, w h i l e the A u s t r a l i a n b e e f and wool

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch002

Table

I I I . Development o f C y c l o d i e n e - B H C - R e s i s t a n c e ,

B o l l Weevil C o t t o n Leafworm Cotton Spodoptera Salt-marsh C a t e r p i l l a r Spiny Bollworm Cotton Aphid Cotton Fleahopper Cotton P e r f o r a t o r Sugarcane Froghopper Cabbage L o o p e r

La. Tex. Egypt Cal. Israel SE USA Tex. Cal. Trinidad Ariz.

House F l y Sheep B l o w f l y Body L o u s e Bed Bug German Roach Blue T i c k Cattle Tick Salt-marsh Mosquitoes I-W § Enc. M o s q u i t o e s M a l a r i a Mosquito

1949-58. Sardinia NSW Japan Italy Tex. S. A f r i c a Queensl d Fla. Cal. Nigeria 1

i n d u s t r y n o t a b l y s u f f e r e d from the f a i l u r e o f l i n d a n e and d i e l d r i n t o c o n t r o l t h e sheep b l o w f l y a n d t h e c a t t l e t i c k . The u s e o f a l d r i n a g a i n s t w i r e w o r m s , r o o t w o r m s and r o o t maggots i n t h e s o i l was s o o n r e w a r d e d b y c y c l o d i e n e - r e s i s t a n c e i n 3 w i r e w o r m s p e c i e s , 4 s p e c i e s o f Diabrotica rootworms i n c o r n f i e l d s , and 6 s p e c i e s o f Eylemya r o o t maggots o n o n i o n s , B r a s s i c a s a n d o t h e r v e g e t a b l e c r o p s ( T a b l e I V ) . C y c l o d i e n e - r e s i s t a n c e i s v e r y d e c i s i v e when i t comes, s o t h a t i t s s p r e a d t h r o u g h t h e i n s e c t p o p u l a t i o n c a n be r e a d i l y s e e n , a s f o r example t h a t o f t h e w e s t e r n c o m r o o t w o r m Diabrotica vivgifeva from Nebraska t o the r e s t o f the midwestern s t a t e s b e t w e e n 1961 a n d 1964. Table

IV.

Cyclodiene-Resistance developed

Coleoptera

Conoderus C. Limonius Diabrotica D. D. D.

fallu vespertinus califbimicus virgifera balteata longicomis 11-punctata

Graphognathus leucoloma Hypera postica

in Soil

I n s e c t s , 1955-65

Diptera S.C.

s.c. Wash. Neb. La. S.D. N.C Ala. Utah

Eylemya antiqua brassicae H. liturata H. platura H. floralis H. arambourgi H. Psila rosae Euxesta notata Merodon equestris

Wis. 111. Ont. B.C. Sask. Kenya Ore. Ont. U.K.

The mechanism o f c y c l o d i e n e - r e s i s t a n c e h a s b e e n v e r y d i f f i c u l t to determine. The h y d r o x y l a t i o n o f a l d r i n a n d d i e l d r i n t o a l d r i n g l y c o l a n d d i e l d r i n t r a n s d i o l i s a s l o w p r o c e s s and i s n o t p e c u l i a r t o r e s i s t a n t s t r a i n s , while the increased l i p o i d content

PESTICIDE CHEMISTRY IN THE 20TH CENTURY

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch002

24

f r e q u e n t l y noted confers only a s l i g h t l y increased t o l e r a n c e . The most l i k e l y mechanism i s t h e s e q u e s t r a t i o n o f t h e c y c l o d i e n e epox­ i d e by b i n d i n g w i t h c e l l u l a r p r o t e i n s , t h u s p r o t e c t i n g t h e p r e s y n ­ a p t i c membranes w h i c h a r e t h e i r p r o b a b l e s i t e o f a c t i o n ( 7 ) . L i n d a n e - r e s i s t a n t s t r a i n s a r e c h a r a c t e r i z e d by an i n c r e a s e d d e t o x i c a t i o n , due t o d e h y d r o c h l o r i n a t i o n t o PCCH and t o d i c h l o r o t h i o p h e n o l s , t h e l a t t e r p r o c e s s p u t t i n g SH g r o u p s i n t o t h e m o l e c u l e (8). However, i n c r e a s e d b r e a k d o w n i s p r o b a b l y o n l y o f s e c o n d a r y i m p o r t a n c e , t h e p r i n c i p a l r e s i s t a n c e mechanism b e i n g t h e same as for the cyclodiene i n s e c t i c i d e s . At t h i s t i m e , r e s i s t a n c e t o the organophosphorus insecticides i s o f prime importance. F i r s t a p p e a r i n g i n 1949 i n t h e twos p o t t e d m i t e Tetranyckus urtioae i n greenhouses, w i t h i n the next d e c a d e i t s p r e a d t o 14 s p e c i e s o f t e t r a n y c h i d m i t e s i n f e s t i n g pome and c i t r u s o r c h a r d s , t o 7 s p e c i e s o f a p h i d s , t o f l i e s , m i d g e s and m o s q u i t o e s , and f i n a l l y t o c o c k r o a c h e s ( T a b l e V ) . W a i t i n g i n t h e w i n g s were s t i l l more s e r i o u s O P - r e s i s t a n c e s i n Heliothis c a t e r p i l l a r s on c o t t o n , and i n Tribolium and Sitophilus beetles on s t o r e d g r a i n ( 9 ) . T a b l e V.

Development o f O r g a n o p h o s p h o r u s - R e s i s t a n c e ,

Two-spotted M i t e European S p i d e r - m i t e P a c i f i c ξ McDaniel Mites Citrus Mite Green Peach A p h i d Green A p p l e A p h i d Walnut δ A l f a l f a Aphids

Conn. Ind. Wash. Cal. Wash. Switz l d Cal. f

f

House F l y Coprophagous F l y Lake Midge German Roach House M o s q u i t o I-W Mosquitoes Enc. M o s q u i t o e s

1949-59. Denmark Congo Fla. Ky. Cameroon Cal. Cal.

The mechanisms o f O P - r e s i s t a n c e i n t h e h o u s e f l y were f o u n d t o d e r i v e not from a decreased o x i d a t i o n o f the t h i o p h o s p h a t e t o the p o w e r f u l p h o s p h a t e a n t i c h o l i n e s t e r a s e , — i n d e e d t h e r e was u s u a l l y a h e i g h t e n e d o x i d a t i o n o f p a r a t h i o n t o paraoxon,for example — , but t o chemical d e g r a d a t i o n o f t h e m o l e c u l a r s t r u c t u r e ( F i g . 2 ) . The mechanism f i r s t t o be d i s c o v e r e d was a p h o s p h a t a s e - t y p e h y d r o l y s i s r e s u l t i n g f r o m t h e g e n e - c o n t r o l l e d c o n v e r s i o n o f an a l i e s t e r a s e f o r w h i c h t h e OP compounds were i n h i b i t o r s , t o an Α-esterase f o r w h i c h t h e s e O P s were s u b s t r a t e s ( 1 0 ) . More i m p o r ­ t a n t , h o w e v e r , was an e n h a n c e d o x i d a t i v e t y p e o f c l e a v a g e o f t h e l e a v i n g g r o u p f r o m t h e p h o s p h o r u s , p r o d u c i n g t h e same m e t a b o l i t e s DPTA o r DPA as t h e e s t e r a s e d i d , b u t b e i n g p u t i n t o e v i d e n c e by t h e a d d i t i o n o f NADH t o m i c r o s o m a l p r e p a r a t i o n s ( 1 1 ) . A t h i r d mechanism was e n h a n c e d d e s a l k y l a t i o n by an a l k y l t r a n s f e r a s e u t i l i z i n g GSH, and f o u n d i n t h e s o l u b l e f r a c t i o n o f homogenates (12). O P - r e s i s t a n t s t r a i n s a l s o u s u a l l y become c h a r a c t e r i z e d by reduced c u t i c u l a r p e n e t r a t i o n , a c h a r a c t e r i s t i c which r e s i s t a n t h o u s e f l i e s u s u a l l y had a l r e a d y g a i n e d a g a i n s t DDT, w h i c h e x t e n d s t o c a r b a m a t e s and p y r e t h r o i d s as w e l l . For r e s i s t a n c e t o malat h i o n , t h e r e i s an a d d i t i o n a l mechanism b a s e d on h y d r o l y s i s o f t h e f

2.

BROWN

Resistance

Mechanisms

against

25

Insecticides

s u c c i n y l e s t e r s i d e - c h a i n (13) b y t h e enzyme l o o s e l y t e r m e d c a r b o x y e s t e r a s e , o r more c o r r e c t l y c a r b o x y l i c - e s t e r h y d r o l a s e . W i t h t h e i n t r o d u c t i o n o f the carbamate i n s e c t i c i d e s i n 1956, r e s i s t a n c e t o c a r b a r y l a p p e a r e d b e t w e e n 1963 a n d 1966 i n a n o r c h ­ a r d l e a f r o l l e r i n New Z e a l a n d , i n t h e c o t t o n l e a f w o r m [Spodoptevd) o f E g y p t , and i n Heliothis viresoens (the s o - c a l l e d tobacco budworm) o n A m e r i c a n c o t t o n ( T a b l e V I ) . R e s i s t a n c e d e v e l o p e d t o OP compounds h a d a l r e a d y g i v e n some c r o s s - t o l e r a n c e t o c a r b a m a t e s Table VI.

R e s i s t a n c e t o C a r b a m a t e s a n d P y r e t h r o i d s , 1958-66.

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch002

Carbaryl

Pyrethrins

T o b a c c o Budworm Cotton Spodoptera L i g h t - b r o w n A p p l e Moth

House F l y T o b a c c o Moth Mushroom F l y

Tex. Egypt N.Z.

Sweden Fla. England

and seemed t o p r e d i s p o s e t h e p e s t f o r a more r a p i d d e v e l o p m e n t o f carbamate-resistance. Resistance t o synergized pyrethrins devel­ oped i n a S w e d i s h h o u s e f l y p o p u l a t i o n j u s t 1 y e a r a f t e r i t h a d b e e n t a k e n o f f a c o n t r o l r e g i m e o f OP compounds f o l l o w i n g a grounding o f o r g a n o c h l o r i n e - r e s i s t a n c e . The mechanism o f c a r b a m a t e - r e s i s t a n c e , f o r m e r l y c o n s i d e r e d t o be e n h a n c e d h y d r o l y s i s ( e . g . c a r b a r y l t o 1 - n a p h t h o l ) , was f o u n d t o d e r i v e almost e x c l u s i v e l y from h y d r o x y l a t i o n a t v a r i o u s p o i n t s on the m o l e c u l e , n o t o n l y t h e a r o m a t i c l e a v i n g group b u t a l s o t h e N - m e t h y l o n t h e c a r b a m a t e ( F i g . 3 ) , a s w e l l a s some d e s m e t h y l a t i o n f o r good measure ( 1 4 ) . P y r e t h r i n - r e s i s t a n c e , a t f i r s t c o n s i d e r e d t o be due t o h y d r o l y s i s o f t h e a l c o h o l - a c i d l i n k a g e , was a l s o f o u n d t o be due t o a n o x i d a t i o n , o c c u r r i n g a t t h e t r a n s m e t h y l group o f the i s o b u t e n y l s i d e - c h a i n o f the chrysanthemic a c i d (15). By 1975, t h e d e v e l o p m e n t o f some t y p e o f r e s i s t a n c e h a d b e e n p r o v e d and r e p o r t e d i n p o p u l a t i o n s o f 268 s p e c i e s o f p e s t a r t h r o ­ pods ( T a b l e V I I ) . O P - r e s i s t a n c e h a d now s p r e a d t o i n v o l v e 85 T a b l e V I I . Numbers o f S p e c i e s w i t h V a r i o u s T y p e s o f R e s i s t a n c e , 1975

Diptera Lepidoptera Hemiptera Acarina Coleoptera Other Orders Total

DDT

Did

OP

Carb

Other

Total

54 17 10 4 10 18 113

77 20 16 8 27 14 162

23 12 20 19 7 4 85

5 6 3 6 3 0 23

3 3 4 8 2 2 22

103 34 42 30 38 21 268

s p e c i e s , and c a r b a m a t e - r e s i s t a n c e t o 23 s p e c i e s . The o r c h a r d a n d g r e e n h o u s e m i t e s , p a r t i c u l a r l y Tetranychus urtiaae, h a d c h a l k e d up s u c h e x o t i c r e s i s t a n c e a s t h o s e t o a z o b e n z e n e , t o t h e d i n i t r o com­ pound b i n a p a c r y l , t o t h e s u l f u r - c o n t a i n i n g o r g a n o c h l o r i n e s , t o t h e f o r m a m i d i n e s , and even t o o x y t h i o q u i n o x ( M o r e s t a n ) . When t h e

PESTICIDE CHEMISTRY IN THE 20TH CENTURY

0, CI

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch002

Oxidation

Dehydrochlorination

* HC-C-CI CI

Figure 1.

Detoxicative mechanisms imparting DDTresistance

Dealkylation

Oxidation Oxidative Cleavage

Hydrolysis

NO2 Figure 2. Detoxicative mechanisms imparting organophosphorus-resistance (e.g. to methyl parathion)

CH

3

I

NH

Dealkylation

I

0 =C 0

Hydroxyjation — Hydrolysis

Figure 3.

Detoxicative mechanisms imparting carhamate-resistance (e.g. to carbaryl)

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch002

2.

BROWN

Resistance

Mechanisms

against

insecticides

27

r e p o r t o f t h e FAO w o r k i n g p a r t y o n r e s i s t a n c e i s p u b l i s h e d some t i m e t h i s y e a r , we w i l l l e a r n t h a t o v e r 300 s p e c i e s o f a r t h r o p o d s h a v e d e v e l o p e d some t y p e o f r e s i s t a n c e i n some p a r t o f t h e w o r l d . The e f f e c t o f t h e s e r e s i s t a n c e s h a s b e e n t o d r i v e c h e m i c a l c o n t r o l f r o m one i n s e c t i c i d e t o t h e n e x t . I n most p a r t s o f t h e N i l e d e l t a t h e c o t t o n l e a f w o r m s c a n s t i l l be c o n t r o l l e d b y some OP compound, s u c h a s c h l o r p y r i f o s , s u p p l e m e n t e d where n e c e s s a r y w i t h the i n s e c t growth r e g u l a t o r D i m i l i n . But i n s o u t h e r n T e x a s , Mexico, N i c a r a g u a a n d P e r u t h e m u l t i p l e r e s i s t a n c e s o f t h e t o b a c c o budworm, and t o a l e s s e x t r e m e d e g r e e o f H. zea a n d Spodoptera sunia, h a v e made e v e n 20 i n s e c t i c i d e a p p l i c a t i o n s a s e a s o n q u i t e w o r t h l e s s , and i n d e e d t h e r e i s l e s s damage t o t h e c o t t o n i f no c h e m i c a l s a r e a p p l i e d a t a l l . The o n l y m a t e r i a l s t h a t c a n be r e l i e d u p o n t o k i l l t h e s e m u l t i r e s i s t a n t H. viresoens arethe dichlorovinyl p y r e t h r o i d NRDC-143 a n d t h e H e l i o t h i s n u c l e a r p o l y h e d r o s i s v i r u s . I t w i l l be n o t e d t h a t t h e p r e s s u r e o f e v e n t s , r e p l a c i n g o r g a n o c h l o r i n e s w i t h 0 P s a n d c a r b a m a t e s , and t h e n r e p l a c i n g them w i t h more b i o l o g i c a l - t y p e a g e n t s , c o n f o r m s t o t h e a s p i r a t i o n s o f t h o s e charged w i t h p r o t e c t i n g t h e environment a g a i n s t p o l l u t i o n . ?

O t h e r p l a n t - f e e d i n g i n s e c t s , s u c h a s t h e c a b b a g e l o o p e r , have p i l e d one r e s i s t a n c e u p o n a n o t h e r , s o t h a t we must l o o k t o p h e r o mones a n d c h e m o s t e r i l a n t s f o r t h e i r c o n t r o l . The w e s t e r n c o r n r o o t w o r m h a s now j o i n e d t h e o n i o n maggot i n g o i n g O P - r e s i s t a n t . R e s i s t a n c e problems on p e s t s o f r i c e i n Japan a r e becoming as severe as t h o s e on c o t t o n i n the Americas. Among i n s e c t s a f f e c t i n g man a n d a n i m a l s , t h e t h r e e m a j o r mosquito v e c t o r s o f d i s e a s e a r e making t h e u s u a l r a k e s progress f r o m one r e s i s t a n c e t o a n o t h e r . The m a l a r i a m o s q u i t o Anopheles albimanus h a s gone t h e w h o l e way, t h e r e s i s t a n c e m a i n l y o w i n g t o t h e p r e s s u r e o f a g r i c u l t u r a l i n s e c t i c i d e s on i t s b r e e d i n g p l a c e s , and t h u s m a l a r i a i s i n c r e a s i n g a g a i n i n C e n t r a l A m e r i c a . The m u l t i p l e r e s i s t a n c e i n some s t r a i n s o f Tribolium i s a s e r i o u s blow to the p r e s e r v a t i o n o f world food s u p p l i e s . S u c c e s s i v e r e s i s t a n c e s have d r i v e n c o n t r o l o f the Boophilus c a t t l e t i c k s a l l t h e way t o OP compounds, a n d f r o m them t o c h l o r phenamidine ( c h l o r d i m e f o r m ) ; a l t h o u g h i t has been r e c e n t l y found that carbaryl i se f f e c t i v e i nc a t t l e dips i f synergized with piperonyl butoxide. The t w o - s p o t t e d m i t e h a s gone t h r o u g h a f a n ­ t a s t i c s e q u e n c e o f a c a r i c i d e s , t h e o n l y ones t o w h i c h r e s i s t a n c e has n o t y e t b e e n r e p o r t e d b e i n g P e n t a c a n d t h e o r g a n o - t i n compound Plictran. The p e s t m o s q u i t o Aedes nigromaoulis o f t h e v a s t San J o a q u i n v a l l e y o f C a l i f o r n i a went r e s i s t a n t t o o r g a n o c h l o r i n e s b y 1951, t o p a r a t h i o n b y 1960, t o f e n t h i o n b y 1965, a n d t o c h l o r p y r i f o s ( D u r s b a n ) b y 1970. A t p r e s e n t r e l i a n c e i s p l a c e d on l a r v i c i d a l o i l s , t h e j u v e n i l e - h o r m o n e mimic methoprene ( A l t o s i d ) and t h e i n s e c t growth r e g u l a t o r d i f l u b e n z u r o n ( D i m i l i n ) , — and on b e t t e r management o f s u r p l u s i r r i g a t i o n w a t e r . R e s i d u a l s p r a y s f o r house­ f l y c o n t r o l , a t f i r s t so s p e c t a c u l a r w i t h t h e o r g a n o c h l o r i n e s , had t o move i n t o t h e OP compounds, w h i c h were t h e n k n o c k e d o u t i n 1

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch002

28

PESTICIDE CHEMISTRY IN THE 20TH CENTURY

s u c c e s s i o n by r e s i s t a n c e . The e x p e r i e n c e i n Denmark b e t w e e n 1951 and 1967 was t h a t e a c h OP compound l a s t e d f o r a b o u t 2 y e a r s , end­ i n g w i t h d i m e t h o a t e , and t h e o n l y way t h a t i t s u s e c o u l d be e x t e n d ­ ed was by p u t t i n g i t i n h o u s e f l y b a i t s i n s t e a d o f r e s i d u a l s p r a y s . I t s h o u l d be c l e a r t o us t h a t t h e d e v e l o p m e n t o f r e s i s t a n c e i s a l w a y s t o be e x p e c t e d t o any i n s e c t i c i d e we may c h o o s e t o a p p l y , but i t i s not i n e v i t a b l e . DDT s t a y e d e f f e c t i v e a g a i n s t t h e E u r o p e a n c o r n b o r e r f o r a t l e a s t 15 y e a r s ( T a b l e V I I I ) and t h e r e a r e s e v e r a l o t h e r e x a m p l e s , i n c l u d i n g d i a z i n o n and t h e w e s t e r n c o r n rootworm i n Nebraska. Some o f t h e s p e c i e s o f b e n e f i c i a l i n s e c t s w h i c h f o r m e r l y s u f f e r e d f r o m i n s e c t i c i d e damage, s u c h as b r a c o n i d p a r a s i t e s , l a d y b e e t l e s , m a y f l y nymphs and h o n e y b e e s , h a v e now d e v e l o p e d c e r t a i n t o l e r a n c e s , w h i l e s e v e r a l o f t h e P h y t o s e i i d m i t e s w h i c h f e e d on t h e p l a n t - f e e d i n g s p i d e r m i t e s a r e b e c o m i n g as r e s i s t a n t as t h e i r p r e y t o OP's and c a r b a m a t e s . Table V I I I .

F a i l u r e s of c e r t a i n i n s e c t s to develop r e s i s t a n c e to c e r t a i n i n s e c t i c i d e s . Field

Eur. Corn Borer F l a . Red S c a l e So. House M o s q u i t o Sugarcane Borer B o l l Weevil W. S p r u c e Budworm W. C o r n Rootworm

DDT parathion Flit-MLO azinphosmethyl malathion mexacarbate diazinon

N. Amer. Cal. Tex. La. W. Tex. Idaho Neb.

1950-65 1951-63

Lab. 34 g e n s 60 g e n ί 6 gen 5 1

1

1964-72 1963-72

T

14 gen* s 1963-73

The t h i n g a b o u t r e s i s t a n c e i s t h a t i t i s i n h e r i t e d , t h a t h i g h l y r e s i s t a n t s t r a i n s s t a y r e s i s t a n t e v e n when r e a r e d f o r g e n e r a t i o n s w i t h o u t e x p o s u r e t o t h e i n s e c t i c i d e , and t h a t t h e y were p r o d u c e d i n t h e f i r s t p l a c e by s u b m i t t i n g n o r m a l s t r a i n s t o t h e p r u n i n g power o f s e l e c t i o n . Thus t h e d e t e r m i n a n t s o f r e s i s ­ t a n c e may be s o u g h t i n t h e genes on t h e chromosomes. The a m a z i n g t h i n g was t h a t r e s i s t a n c e , w h i c h was t h o u g h t a priori t o be due t o a l l e l e s o f a number o f m i n o r genes ( i . e . p o l y f a c t o r i a l ) , t i m e and t i m e a g a i n t u r n e d o u t t o be due t o a s i n g l e d e c i s i v e gene ( i . e . monofactorial). T h i s was f i r s t shown i n 1953 f o r D D T - r e s i s t a n c e i n t h e h o u s e f l y and Drosophila, and i n 1956 f o r O P - r e s i s t a n c e i n t h e Tetranyehus m i t e s . S u b s e q u e n t s t u d i e s on t h e g e n e t i c s o f r e s i s t a n c e i n a v a r i e t y o f s p e c i e s showed t h a t t h e gene a l l e l e s r e s p o n s i b l e f o r O P - r e s i s t a n c e and c a r b a m a t e - r e s i s t a n c e were a l w a y s d o m i n a n t , t h o s e f o r c y c l o d i e n e - r e s i s t a n c e were a l w a y s i n t e r m e d i a t e i n e x p r e s s i o n , w h i l e D D T - r e s i s t a n c e genes t u r n e d o u t t o be d o m i n a n t i n some s p e c i e s and r e c e s s i v e i n o t h e r s ( 1 6 ) . By t h e u t i l i z a t i o n o f m a r k e r s t r a i n s b e a r i n g v i s i b l e m u t a n t s , w h i c h a r e a v a i l a b l e f o r t h e h o u s e f l y and t h e i r p o s i t i o n on t h e 6 chromosomes i n t h a t s p e c i e s (17) i t became p o s s i b l e t o l o c a t e t h e genes r e s p o n s i b l e f o r t h e v a r i o u s D D T - r e s i s t a n c e mechanisms already described (Fig. 4). The r e s i s t a n c e due t o d e h y d r o c h l o r -

BROWN

Resistance

Mechanisms

against

Insecticides

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch002

OX

a.

Deh

kdr

X o r Y I Figure 4.

Ε

(DR )

(tin)

II

4

(md)

υ

ΠΖ

31

Location of the genes for various resistances on the chromosomes of the housefly

PESTICIDE CHEMISTRY IN THE 20TH CENTURY

i n a t i o n was f o u n d t o be l o c a t e d o n chromosome 2 b e t w e e n t h e mark­ e r s aristapedia a n d carmine. The hétérozygotes f o r t h i s gene a l l e l e , c a l l e d Deh, h a d h a l f a s much D D T - d e h y d r o c h l o r i n a s e a s t h e r e s i s t a n t homozygotes (18). The gene f o r enhanced m i c r o s o m a l o x i d a t i o n md was f o u n d t o be l i n k e d w i t h m a r k e r s o n chromosome 5, b u t i t c a n n o t y e t be l o c a t e d i n a p r e c i s e p o s i t i o n on t h a t chromo­ some; a n o t h e r gene f o r o x i d a t i o n i s l o c a t e d a t t h e end o f chromo­ some 2. The gene f o r r e d u c e d n e r v e s e n s i t i v i t y ( e s s e n t i a l l y k n o c k d o w n - r e s i s t a n c e ) was p r e c i s e l y l o c a t e d o n chromosome 3, a l o n g w i t h t h e gene (tin) f o r r e d u c e d c u t i c u l a r p e n e t r a t i o n . (Cyclo­ d i e n e - r e s i s t a n c e i n t h e h o u s e f l y i s l o c a t e d o n chromosome 4.) E a c h D D T - r e s i s t a n c e gene compounds w i t h t h e o t h e r s t o p r o d u c e r e s i s t a n c e i n t e n s i t i e s w h i c h a r e t h e m u l t i p l e r a t h e r t h a n t h e sum o f each c o n t r i b u t o r . The D D T - r e s i s t a n c e s i n o t h e r s p e c i e s have t u r n e d o u t t o b e due e i t h e r t o o x i d a t i o n , a s i n Drosophila a n d t h e German c o c k ­ r o a c h , o r t o d e h y d r o c h l o r i n a t i o n w i t h reduced p e n e t r a t i o n added, as i n t h e p i n k b o l l w o r m a n d t h e t r o p i c a l h o u s e m o s q u i t o ( T a b l e 9 ) . I n Heliothis virescens one s t r a i n was c h a r a c t e r i z e d b y d e h y d r o ­ c h l o r i n a t i o n , another by reduced p e n e t r a t i o n (19). T a b l e IX.

Mechanisms o f D D T - R e s i s t a n c e i n t h e H o u s e f l y a n d other Insects.

+

+ +

+

+

Culex tarsalis

+

Culex fatigans

Deh ( I I ) md (V) ox ( I I ) hdr ( I I I ) tin ( I I I )

Pomace fly

1

Dehydrochlorin η Oxidation Oxidation I n s e n s i t i v e Nerve Reduced P e n e t r ' n

Pink Bollworm

Resistance Mechanism

Tobacco Budworm

Housefly Gene

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch002

30

+ +

+

F o r O P - r e s i s t a n c e i n t h e h o u s e f l y , t h e gene t h a t d e t e r m i n e s t h e c o n v e r s i o n o f a l i e s t e r a s e i n t o a n Α-esterase, c a l l e d a , i s l o c a t e d o n chromosome 2 v e r y c l o s e t o t h e Deh gene. O f t h e two genes f o r o x i d a t i o n f o u n d i n O P - r e s i s t a n t s t r a i n s , t h e gene ox (diagnosable by the e p o x i d a t i o n o f a l d r i n t o d i e l d r i n ) i s e v i d e n t ­ l y more i m p o r t a n t t h a n md ( f i r s t f o u n d a s d e t e r m i n i n g a sesamexi n h i b i t e d DDT-resistance). D e s a l k y l a t i o n was f o u n d a t t r i b u t a b l e t o a gene ( c a l l e d g) v e r y c l o s e t o a a n d Deh, a n d many O P - r e s i s t a n t s t r a i n s have a l s o a c q u i r e d t h e r e d u c e d p e n e t r a t i o n gene a l l e l e tin. Thus g e n e t i c s c a n h e l p u s s o r t o u t t h e r e s i s t a n c e mechanisms i n a given r e s i s t a n t s t r a i n o r population. The a b i l i t y t o c l e a v e o f f t h e l e a v i n g g r o u p b y a p r o c e s s p r e ­ s u m a b l y h y d r o l y t i c h a s b e e n d e t e c t e d i n a number o f O P - r e s i s t a n t species (Table X). I n t h e t o b a c c o budworm c l e a r e v i d e n c e f o r OPr e s i s t a n c e b e i n g a s s o c i a t e d w i t h o x i d a t i v e c l e a v a g e was o b t a i n e d from the a c t i o n o f microsomes on t h e p h o s p h o r o t h i o n a t e c h l o r p y r i f o s

2.

BROWN

T a b l e X.

Resistance

against

31

Insecticides

Mechanisms o f O P - R e s i s t a n c e i n t h e H o u s e f l y a n d other Arthropods.

Oxidation Oxidation Hydrolysis Desalkylation Reduced P e n e t r ' n I n s e n s i t i v e ChE

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch002

Mechanisms

md (V) ox ( I I ) a (II) g (II) tin ( I I I )

+ + +

(+) +

+

+ +

(+)

+ +

+

as a s u b s t r a t e ( 2 0 ) , w h i l e e v i d e n c e f o r i n c r e a s e d h y d r o l y s i s was o b t a i n e d o n t h e p h o s p h a t e GC-6506 a s a s u b s t r a t e ( 2 1 ) . E v i d e n c e ( 2 2 ) f o r d e s a l k y l a t i o n h a s b e e n f o u n d i n t h e p r e d a c e o u s m i t e Amblyseius fallaois a s w e l l a s i n Heliothis. A mutant c h o l i n e s t e r a s e i n s e n ­ s i t i v e t o OP i n h i b i t i o n was o r i g i n a l l y f o u n d n o t t o be a r e s i s ­ t a n c e mechanism i n t h e h o u s e f l y , b u t t o c h a r a c t e r i z e some r e s i s ­ t a n t s t r a i n s o f Tetranyehus urtieae (23) and most O P - r e s i s t a n t s t r a i n s o f t h e A u s t r a l i a n c a t t l e t i c k (24). I t has r e c e n t l y been f o u n d t o be a mechanism i n t h e sheep b l o w f l y ( 2 5 ) , t h e m a l a r i a m o s q u i t o Anopheles albimanus, and a New Y o r k s t r a i n o f t h e h o u s e f l y (27). So we now u n d e r s t a n d how f i e l d p o p u l a t i o n s a n d l a b o r a t o r y s t r a i n s exposed g e n e r a t i o n a f t e r g e n e r a t i o n t o an i n s e c t i c i d e o r i n s e c t i c i d e s a c c u m u l a t e mutant a l l e l e s making f o r r e s i s t a n c e . I f s u s c e p t i b l e genotypes s t i l l remain i n t h e s t r a i n s , they u s u a l l y r e v e r t s i n c e t h e new r e s i s t a n c e genome, b e i n g a b n o r m a l , g e n e r a l l y does n o t do a s w e l l and i s t h u s c o n s t a n t l y d i l u t e d w i t h i n t h e p o p u l a t i o n o r by i m m i g r a t i o n from o u t s i d e . B u t s t r a i n s and popu­ l a t i o n s t h a t have r e v e r t e d t o s u s c e p t i b i l i t y r e c o v e r t h e i r r e s i s ­ t a n c e a l m o s t i m m e d i a t e l y when t h e o r i g i n a l i n s e c t i c i d e i s r e a p p l i e d ; i n 1956 t h e D a n i s h h o u s e f l y p o p u l a t i o n s w h i c h h a d r e v e r t e d s i n c e o r g a n o c h l o r i n e s were d i s c o n t i n u e d i n 1951 r e c o v e r e d t h e i r r e s i s t a n c e t o DDT a n d c h l o r d a n e a f t e r j u s t one p a r t i a l l y successful reapplication. The m u l t i r e s i s t a n t s t r a i n s now e x t a n t a l s o show a c e r t a i n cross-tolerance, but not resistance, t o the third-generation i n s e c t i c i d e s such as t h e j u v e n i l e - h o r m o n e mimics and o t h e r s o c a l l e d i n s e c t g r o w t h r e g u l a t o r s , a s was f o u n d i n s t r a i n s o f t h e h o u s e f l y , f l o u r b e e t l e a n d t o b a c c o budworm. Resistance t o the JH m i m i c m e t h o p r e n e and Monsanto-585 h a s b e e n i n d u c e d b y l a b o r a t o r y

s e l e c t i o n o f Culex tarsalis

(28) and Culex pipiens

( 2 9 ) , and t o

Monsanto-585 i n Culex quinquefaseiatus (30). Whatever i n s e c t o r IGR i s c h o s e n , t h e r e s u l t o f e x p o s u r e t o s e l e c t i v e d o s e s i n s u c ­ c e s s i v e g e n e r a t i o n s i s u s u a l l y t h e development o f r e s i s t a n c e , r e p e a t i n g o u r p r e v i o u s e x p e r i e n c e w i t h c h e m o s t e r i l a n t s , and t h e

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch002

32

PESTICIDE CHEMISTRY IN THE 20TH CENTURY

same a p p l i e s t o d i f l u b e n z u r o n ( D i m i l i n ) , t h e new c h i t i n s y n t h e t a s e i n h i b i t o r d e r i v e d from u r e a . Now f o r t h e F o r w a r d L o o k , t h e p r o j e c t i o n o f e x p e c t a t i o n s f o r the remainder o f t h i s century. We c a n e x p e c t t h e c o n t i n u e d s p r e a d and a c c u m u l a t i o n o f r e s i s t a n c e s i n d i r e c t p r o p o r t i o n t o o u r u s e o f c h e m i c a l s , w h i c h i n t h e U n i t e d S t a t e s w i l l be organophosphorous, c a r b a m a t e and f o r m a m i d i n e compounds, p r o b a b l y w i t h e n d o s u l f a n , m e t h o x y c h l o r and l i n d a n e among t h e o r g a n o c h l o r i n e s , some p y r e t h r o i d s , and p e r h a p s w i t h d i f l u b e n z u r o n e and some J H m i m i c s among t h e i n s e c t g r o w t h r e g u l a t o r s . S i n c e new c l e a r a n c e s a r e b a r e l y k e e p i n g up w i t h s u s p e n s i o n s , we must make what we h a v e l a s t as l o n g as p o s s i b l e . S p r a y c a l e n d a r s w h i c h c h o o s e t h e l e a s t p e r ­ s i s t e n t o f t h e OP compounds, s u c h as t r i c h l o r f o n , w i l l n o t e x e r t s e l e c t i o n p r e s s u r e f o r so l o n g a p e r i o d a f t e r a p p l i c a t i o n as t h e more p e r s i s t e n t o n e s , and a r e e a s i e r on t h e p r e d a t o r s and p a r a ­ sites. T h i s i s the i n t e n t i o n o f the i n t e g r a t e d c o n t r o l systems now b e i n g d e v e l o p e d and f o l l o w e d . We may h a v e l e a r n e d f r o m t h e e r r o r s o f t h e p a s t t o be s u f f i c i e n t l y n e r v o u s a b o u t o u r t a r g e t p o p u l a t i o n s , e v e r y t i m e we p u t them u n d e r i n s e c t i c i d e p r e s s u r e , t o go t o t h e t r o u b l e o f m o n i t o r i n g t h e i r s u s c e p t i b i l i t y s t a t u s . S t a n d a r d t e s t methods f o r r e s i s t a n c e h a v e been d e v e l o p e d by FAO (31) and by t h e E n t o m o l o g i c a l S o c i e t y o f A m e r i c a (32) f o r many i m p o r t a n t a r t h r o p o d p e s t g r o u p s , and more a r e b e i n g d e v e l o p e d ( T a b l e X I ) . T h e i r s y s t e m a t i c u s e a t r e g u l a r i n t e r v a l s s h o u l d be an i n t e g r a l p a r t o f p e s t management. F o r i n s e c t s o f p u b l i c - h e a l t h i m p o r t a n c e , t e s t methods h a v e been made a v a i l a b l e f o r a l l s p e c i e s g r o u p s by WHO ( 3 3 ) , and t h e s e a r e s y s t e m a t i c a l l y u s e d , l a r g e l y b e c a u s e t h e y a r e s i m p l e t o p e r f o r m and t e s t k i t s a r e a v a i l a b l e t o c a r r y them o u t . I t i s j u s t p o s s i b l e t h a t i n the l a s t quarterc e n t u r y o f t h i s m i l l e n i u m , a g r i c u l t u r e d e p a r t m e n t s o f s t a t e s and n a t i o n s may be s u f f i c i e n t l y w e l l - i n f o r m e d a b o u t t h e o v e r a l l n a t u r e o f t h e r e s i s t a n c e p r o b l e m , t h a t t r o u b l e may be d e t e c t e d when and where i t i s i m m i n e n t and t h e a p p r o p r i a t e change made i n t h e c o n ­ t r o l method b e f o r e i t becomes a r e a l i t y . Table

X I . T e s t methods f o r s u s c e p t i b i l i t y

FAO

Methods

ESA

Eylemya spp. ξ Psila rosae Chilo suppressalis Myzus persicae Nephotettix cincticeps Tribolium oastaneum Spodoptera littorales Cocoa M i r i d s Tetranychid mites

Laspeyresia

pomonella

Leptinotarsa 10-lineata Adult Locusts Luc-ilia larvae $ adults Beetles i n stored cereals

levels to

insecticides.

Methods

Developed

Anthonomus grandis Heliothis zea & viresoens Hypera postica Diabrotica spp. Developing

Conotrachelus

nenuphar

Lygus bugs A n t h o c o r i d bugs Scarabaeid grubs P h y t o s e i i d mites

2.

BROWN

Resistance

Mechanisms

against Insecticides

33

Literature Cited 1. 2. 3. 4. 5.

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch002

6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28.

Hough, W.S. J. Agric. Res. (1934) 48, 533-553. Yust, H.R. and F.F. Shelden. Ann. Entomol. Soc. Amer. (1952) 45, 220-228. Wiesmann, R. M i t t . Schweiz. Entomol. Ges. (1947) 20, 484-504. Lipke, H. and C.W. Kearns. J. B i o l . Chem. (1959) 234, 2123-2125. Tsukamoto, Μ., T. Narahashi and T. Yamasaki. Botyu-Kagaku (1965) 30, 128-132. Oppenoorth, F.J. and N.W.H. Houx. Ent. Exp. Applic. (1968) 11, 81-93. Matsumura, F. and M. Hayashi. Science (1966) 153, 757-759. Bradbury, F.R. and H. Standen. Nature (1959) 183, 983-984. Brown, A.W.A. In R. White-Stevens (ed.) "Pesticides i n the Environment", Marcel Dekker, New York (1971) Vol I , Part I I , pp. 455-552. van Asperen, K. Ent. Exp. Applic. (1964) 7, 205-214. El-Bashiev, S. and F.J. Oppenoorth. Nature (1969) 223, 210-211. Hollingsworth, R.M., R.L. Metcalf and T.R. Fukuto. J. Agr. Food Chem. (1967) 15, 250-255. Matsumura, F. and C.J. Hogendijk. Ent. Exp. Applic. (1964) 7, 179-193. Shrivastava, S.P., M. Tsukamoto and J.E. Casida. J. Econ. Entomol. (1969) 62, 483-498. Yamamoto, I., E.C. Kimmel and J.E. Casida. J. Agr. Food Chem. (1969) 17, 1227-1236. Brown, A.W.A. Wld. Rev. Pest Control (1967) 6, 104-114. Plapp, F.W. Annu. Rev. Entomol. (1976) 21, 179-197. Lovell, J.B. and C.W. Kearns. J. Econ. Entomol. (1959) 52, 931-935. Vinson, S.B. and J.R. Brazzel. J. Econ. Entomol. (1966) 59, 600-604. Whitten, C.J. and D.L. B u l l . Pesticide Biochem. Physiol. (1974) 4, 266-274. B u l l , D.L. and C.J. Whitten. J. Agr. Food Chem. (1972) 20, 561-564. Motoyama, N., G.C. Rock and W.C. Dauterman. Pesticide Biochem. Physiol. (1972) 1, 205-215. Smissaert, H.R. Science (1964) 143, 129-131. Nolan, J., H.J. Schnitzerling and C.A. Schuntner. Pesticide Biochem. Physiol. (1972) 2, 85-94. Schuntner, C.A. and W.J. Roulston. Austral. J. B i o l . S c i . (1968) 21, 173-176. Ayad, H. and G.P. Georghiou. J. Econ. Entomol. (1975) 68, 295-297. T r i p a t h i , R.K. Pesticide Biochem. Physiol. (1976) 6, 30-34. Georghiou, G.P., C.S. L i n , C.S. Apperson and M.E. Pasternak. Proc. C a l i f . Mosq. Control Assoc. (1974) 42, 117-118.

34

29. 30. 31. 32.

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33.

PESTICIDE CHEMISTRY IN THE 20TH CENTURY

Brown, T.M. and A.W.A. Brown. J. Econ. Entomol. (1974) 67, 799-801. Hsieh, M.Y., C.D. Steelman and P.E. S c h i l l i n g . Mosquito News (1974) 34, 416-420. Food and Agriculture Organization. Plant Protection B u l l . (1969-71) 17, 83-89 & 129-131. 18, 16-18, 53-55 & 107-113. 19, 15-18, 32-35 & 62-65. 22, 103-126. Entomological Society of America. B u l l . Entomol. Soc. Amer. (1967 & 1970) 14, 31-37 & 16, 147-153. World Health Organization. Wld. Hlth. Org. Techn. Rep. Ser. No 443 (1970), 279 pp.

3 Development of the American Herbicide Industry E. F. A D L E R , W. L. W R I G H T , and G. C. K L I N G M A N

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch003

Lilly Research Laboratories, E l i Lilly and Co., Greenfield, Ind. 46140

From the b e g i n n i n g of r e c o r d e d history, weeds have limited man's food s u p p l y and have imposed a heavy l a b o r b u r d e n . N e a r l y all of e a r l y man's time was no doubt spent in o b t a i n i n g f o o d . N a t u r a l food sources permitted man's survival, even though p e r i o d s of starvation must have been common. From 10,000 B . C . to 6,000 B.C., man began to cultivate c r o p s by primi­ tive methods ( F i g . 1) ( 1 ) . About 6,000 B.C., he f a s h i o n e d hand-weeding tools. Around 1,000 B.C., a n i m a l - p o w e r e d implements were i n t r o d u c e d . P r i o r to this t i m e , human energy was the s o l e source available f o r weed control. In the 2,900 y e a r s between 1,000 B . C . and 1900 A.D., man l e a r n e d to use a n i m a l s to till the soil and to c o n t r o l weeds. Improved tools l e d to b e t t e r cul­ tural methods and even g r e a t e r d e c r e a s e s in the human effort r e q u i r e d f o r weed control. By 1920, in this c o u n t r y , perhaps 40% of the energy i n p u t to weed con­ trol was human, 60% a n i m a l . In the 1920's, tractors were i n t r o d u c e d as new agricultural tools and were u s e d , among o t h e r t h i n g s , to i n c r e a s e the amount of l a n d t h a t one man c o u l d cultivate. By 1947, tractors with cultivators re­ placed perhaps 70% of the hand and a n i m a l l a b o r f o r m e r l y r e q u i r e d f o r weed control. A f t e r World War I I , modern c h e m i c a l weed c o n t r o l was i n t r o d u c e d . C h e m i c a l h e r b i c i d e s not o n l y reduced the human energy r e q u i r e d , but a l s o reduced the amount of m e c h a n i c a l c u l t i v a t i o n . We e s t i m a t e human energy i n p u t f o r o v e r a l l weed c o n t r o l i n the U n i t e d S t a t e s today at no more than 5%, w i t h o n l y a t r a c e of a n i m a l energy i n p u t ; m e c h a n i c a l , at 40% and d e c l i n i n g ; w i t h h e r b i c i d e s r e s p o n s i b l e f o r the r e m a i n d e r . Thus, the

39

PESTICIDE CHEMISTRY IN THE 20TH CENTURY

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40

Figure 1.

History of weed control

50

10,000 B.C. 6,000 B.C. 1,000 B.C. REMOVAL BY HAND

Figure 2.

PRIMITIVE HAND TOOLS INTRODUCED

1920 A.D.

ANIMAL-POWERED MECHANICALLY IMPLEMENTS POWERED INTRODUCED IMPLEMENTS (TRACTORS) INTRODUCED

1947 AD.

1975 A.D.

CHEMICAL WEED CONTROL INTRODUCED

PRESENT DAY

Crop energy output per man (number of people fed by one farmer)

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch003

3.

ALDER ET

AL.

American

Herbicide

41

Industry

h i s t o r y of weed c o n t r o l has seen a s h i f t from the use o f a l l human e f f o r t , to animal power, to petroleump o w e r e d e q u i p m e n t , a n d now to chemical herbicides. U s i n g t h e same t i m e f r a m e s , t h e c r o p e n e r g y o u t p u t p e r man as m e a s u r e d by t h e n u m b e r o f p e o p l e f e d by one farmer i s presented in Figure 2. E a r l y man did w e l l to feed himself. When he b e g a n t o c u l t i v a t e c r o p s , by 6 , 0 0 0 B.C., o n e man was a b l e t o p r o v i d e a l i t t l e m o r e f o o d t h a n he himself could eat. H e n c e , some t i m e was available for fash­ i o n i n g t o o l s and for other a c t i v i t i e s . By 1,000 B.C., o n e man c o u l d , i n many p a r t s o f t h e w o r l d , feed as many as t h r e e p e o p l e . Again, l e t ' s move a h e a d 2,900 y e a r s t o t h e U n i t e d S t a t e s ; we find t h a t by 1920 one f a r m e r was c a p a b l e of f e e d i n g e i g h t p e o p l e ; by 1947, 16; and t o d a y , a t l e a s t 50 p e o p l e . The m o s t recent of t h e s e advances would have been i m p o s s i b l e without c h e m i c a l weed control. The b e n e f i t s f r o m h e r b i c i d e u s a g e a r e many (Table I ) . Table

Hand

I.

Herbicides

tillage

costs

reduce

Harvest

costs

Mechanical costs

tillage

Grain

Fertilizer

costs

Transportation and storage costs

Irrigation

costs

Crop

losses

yield

drying

costs

Number of laborers required Acres needed production

for

crop

They i n c l u d e a r e d u c t i o n of hand t i l l a g e costs. B e f o r e h e r b i c i d e s , h a n d h o e i n g was regularly practiced in a l l vegetable c r o p s and i n most a g r o n o m i c crops. In vegetable c r o p s , h a n d h o e i n g m i g h t c o s t as much as $300 or more per a c r e f o r the s e a s o n . With h e r b i c i d e s , t o t a l w e e d i n g c o s t s c a n be r e d u c e d t o a s m a l l fraction of t h i s sum. B e f o r e h e r b i c i d e s , 20 h o u r s o f h o e labor t i m e p e r a c r e i n c o t t o n was u s u a l and weedy fields c o u l d r e q u i r e 100 hours. Y o u may have heard that h e r b i c i d e s would not be used i n underdeveloped c o u n t r i e s where l a b o r i s avail­ a b l e and inexpensive. But our e x p e r i e n c e has been t o the c o n t r a r y . N o w h e r e i n t h e w o r l d do p e o p l e l i k e to

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42

PESTICIDE CHEMISTRY IN THE 20TH CENTURY

p u l l w e e d s b y h a n d a n d move s o i l f o r weed control. The a b o l i s h m e n t o f t h e d r u d g e r y o f s t o o p l a b o r , and the consequent h i g h e r crop y i e l d s a f f o r d e d by h e r b i ­ c i d e s , u l t i m a t e l y b e t t e r s t h e l o tof t h e hoe-hand. It a l s o r e l e a s e s c h i l d r e n t o a t t e n d s c h o o l and w i v e s to b e t t e r t e n d t h e i r f a m i l i e s o r f i n d more p r o f i t a b l e employment. H e r b i c i d e s r e d u c e m e c h a n i c a l t i l l a g e c o s t s (2^) . E a c h y e a r i n t h e U n i t e d S t a t e s , 250 b i l l i o n tons of s o i l a r e moved, much o f i t s e v e r a l t i m e s , i n t i l l a g e and c u l t i v a t i o n o p e r a t i o n s . T h i s amount o f s o i l w o u l d make a r i d g e 100 f e e t h i g h a n d one m i l e w i d e f r o m New Y o r k t o S a n F r a n c i s c o . The movement o f t h i s s o i l each year i s the world's l a r g e s t m a t e r i a l handling operation. At least one-half of this s o i l moving f u n c t i o n i s p r a c t i c e d s o l e l y f o r t h e c o n t r o l of weeds. Herbicides reduce f e r t i l i z e r costs. Weeds a r e in d i r e c t competition w i t h crop p l a n t s f o r n u t r i e n t s from the s o i l . W i t h o u t weed c o n t r o l , f a r m e r s w o u l d be f e r t i l i z i n g t h e crop and t h e weeds. Herbicides reduce i r r i g a t i o n costs. Weeds a r e a l s o i n d i r e c t c o m p e t i t i o n w i t h crop p l a n t s f o r water. Thus, i r r i g a t i o n w a t e r used by weeds i s n o t a v a i l a b l e for the production of a crop. Crop y i e l d l o s s e s due t o weeds v a r y a c c o r d i n g t o the c o m p e t i t i v e n e s s o f t h e c r o p , t h e weeds present, and t h e p o p u l a t i o n d e n s i t y o f t h e w e e d s . Weed c o n t r o l is extremely important t o any good p r o g r a m o f c r o p production. Crop l o s s due t o weed c o m p e t i t i o n c a n be s u b s t a n t i a l (_3) . As an e x a m p l e , i t h a s been estimated t h a t n e a r l y 100 m i l l i o n b u s h e l s of soybeans, or the e q u i v a l e n t o f t h e p r o d u c t i o n f r o m 4,000,000 a c r e s , was l o s t due t o weed c o m p e t i t i o n i n t h e y e a r 1970. Herbicides reduce harvest costs. Weeds o f t e n m a k e i t i m p o s s i b l e t o h a r v e s t a c r o p a n d may r e s u l t i n t o t a l crop f a i l u r e . Weeds w r a p a r o u n d , c l o g , a n d otherwise i n t e r f e r e with harvesting equipment, result­ ing i n longer running times, greater fuel consumption, and i n c r e a s e d h a r v e s t costs. Herbicides reduce grain drying costs. Fields t h a t a r e f i l l e d w i t h green weeds as t h e crop i s matur­ ing and d r y i n g r e s u l t i n t h e g r a i n d r y i n g more s l o w l y . Weed s e e d s a n d s t e m s t h a t f i n d t h e i r w a y i n t o t h e grain b i n are usually high i n moisture content. These g r e e n weed p a r t s i n c r e a s e t h e p o t e n t i a l f o r g r a i n s p o i l a g e and t h e c o s t of d r y i n g .

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3.

ALDER ET AL.

American

Herbicide

43

Industry

Herbicides reduce t r a n s p o r t a t i o n and storage costs. A good example o f t h e t r a n s p o r t a t i o n and storage c o s t s o f weed s e e d s was g i v e n b y a C a n a d i a n weed s c i e n t i s t (_1) . He r e p o r t e d that despite herbi­ c i d e u s a g e a n d g r a i n - c l e a n i n g p r o c e s s e s , 33 r a i l r o a d c a r l o a d s o f weed seeds a r e t r a n s p o r t e d across Canada from e l e v a t o r s t o ports each day. F i n a l l y , h e r b i c i d e s r e d u c e t h e number o f a c r e s needed f o rcrop production. I f , t h r o u g h b e t t e r weed c o n t r o l , we c a n o b t a i n h i g h e r y i e l d s , we c a n r e d u c e the number o f a c r e s r e q u i r e d t o p r o d u c e a g i v e n amount o f f o o d . The h i s t o r y of the use of chemicals f o r vegeta­ t i o n c o n t r o l goes back t o a n t i q u i t y . We k n o w t h a t t h e Romans s a l t e d t h e f i e l d s o f t h e i r d e f e a t e d Carthagin­ ian foe. P r o b a b l y s a l t was u s e d much e a r l i e r a s a soil sterilant. The f i r s t r e c o r d e d recommendation o f s o d i u m c h l o r i d e f o r weed c o n t r o l was i n Germany i n 1854 (4·) ( T a b l e I I ) . The n e x t y e a r s u l f u r i c a c i d was recommended and was u s e d f o r s e v e r a l d e c a d e s a r o u n d the world f o r s e l e c t i v e weed c o n t r o l i n c e r e a l s a n d onions. Sodium a r s e n i t e was i n t r o d u c e d i n 1902 by t h e Army C o r p s o f E n g i n e e r s f o r t h e c o n t r o l o f w a t e r hyacinth i n Louisiana. The e f f e c t i v e n e s s o f c a r b o n d i s u l f i d e a s a s o i l f u m i g a n t f o r weed c o n t r o l was discovered i n 1 9 0 6 . I t was used i n H a w a i i , California, and some o f t h e w e s t e r n s t a t e s . The peak usage was r e a c h e d i n I d a h o i n 1936 when 350,000 g a l l o n s w e r e applied. P e t r o l e u m o i l s were used as e a r l y as 1914, and t h e y h a v e b e e n w i d e l y u s e d i n i r r i g a t i o n a n d drainage d i t c h e s i n t h e western s t a t e s and as s e l e c ­ tive herbicides i n carrots. Table

Year

II.

Chemicals

first

used

as

herbicides

Introduced

Chemical

1854 1855 1902 1906 1914 1923 1933 1940

Sodium c h l o r i d e Sulfuric acid Sodium a r s e n i t e Carbon disulfide Petroleum oils Sodium c h l o r a t e Dinitrophenol compounds Ammonium s u l f a m a t e

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch003

44

PESTICIDE CHEMISTRY IN THE 20TH CENTURY

S o d i u m c h l o r a t e was f i r s t used i n France i n 1923. I t has been u s e d c h i e f l y as a s o i l s t e r i l a n t f o r c o n ­ t r o l of d e e p - r o o t e d p e r e n n i a l weeds. Dinitrophenol was f i r s t u t i l i z e d i n F r a n c e i n 1933 f o r the control of a n n u a l b r o a d l e a f weeds i n c e r e a l s . I t has been e x t e n s i v e l y e m p l o y e d i n c e r e a l s , l e g u m e s , and f l a x i n the n o r t h e r n United S t a t e s . Ammonium s u l f a m a t e has b e e n u s e d f o r t h e control of woody p l a n t s s i n c e 1940. These o l d e r compounds each r e p r e s e n t e d attempts at weed c o n t r o l , s o m e t i m e s s e l e c t i v e weed control, through chemicals. T h e l a s t 30 y e a r s h a s b e e n a t i m e of r a p i d d e v e l o p m e n t o f new herbicides, mainly organic chemicals, i n the United S t a t e s . O v e r 40 b a s i c a n d specialty chemical manufacturers (such as pharmaceuti­ cal, o i l , r u b b e r , and p a i n t c o m p a n i e s ) h a v e partici­ p a t e d i n t h i s c h e m i c a l r e v o l u t i o n of weed control. M o r e t h a n 130 d i f f e r e n t o r g a n i c c h e m i c a l s a r e c u r r e n t ­ l y e m p l o y e d a s h e r b i c i d e s i n t h e U.S. A l l of the main f a m i l i e s of o r g a n i c compounds a r e r e p r e s e n t e d : aro­ m a t i c , a l i p h a t i c , and h e t e r o c y c l i c . Herbicidal a c t i v i t y i s found i n a v a r i e t y of c l a s s e s of compounds: h a l o a l i p h a t i c , p h e n o x y , and b e n z o i c a c i d s ; carbamates; d i n i t r o a n i l i n e s ; a c e t a n i l i d e s ; amino triazines; q u a t e r n a r y p y r i d i n i u m s a l t s ; u r a c i l s ; and u r e a s . A few s e l e c t e d key e x a m p l e s a r e r e v i e w e d below. 2,4-D, i n t r o d u c e d by Amchem i n 1 9 4 5 , was the f i r s t of a s e r i e s of p h e n o x y a c e t i c a c i d h e r b i c i d e s (Fig. 3). These compounds a r e h i g h l y effective h e r b i c i d e s t h a t s e l e c t i v e l y k i l l b r o a d l e a f weeds w i t h l i t t l e o r no damage t o g r a s s e s . They a r e s t i l l widely used to c o n t r o l b r o a d l e a f weeds i n c o r n , wheat, b a r l e y , sorghum, sugarcane, g r a s s p a s t u r e s , and i n turf. Dalapon, a c h l o r i n a t e d a l i p h a t i c a c i d , was intro­ d u c e d b y Dow C h e m i c a l i n 1953 (Fig. 3). I t i s a grass k i l l e r , c o n t r o l l i n g tough p e r e n n i a l grasses such as j o h n s o n g r a s s , b e r m u d a g r a s s , and q u a c k g r a s s . It p o s s e s s e s a l m o s t no c r o p selectivity. D i u r o n was i n t r o d u c e d by du P o n t i n 1954 (Fig. 3). I t i s one o f a s e r i e s o f s u b s t i t u t e d u r e a herbicides. Diuron i s a p p l i e d preemergence to crops such as c o t t o n , a l f a l f a , g r a p e s , f r u i t and nut c r o p s . Foliar a c t i v i t y i s e n h a n c e d when a s u r f a c t a n t i s added t o the spray. EPTC was i n t r o d u c e d by S t a u f f e r i n 1959 (Fig. 3). I t i s a t h i o c a r b a m a t e and an i m p o r t a n t member o f a l a r g e f a m i l y of h e r b i c i d e s . Thiocarbamates are usually soil incorporated. EPTC i s u s e d i n c r o p s such

ALDER ET AL.

American

Herbicide

Industry

Dalapon 2,4-D

CH3-CCI2-COOH (Dow. 1953)

CI-^~~^0-CH -COOH 2

Cl

EPTC

(Amchem. 1945)

H C-H C-H C\ ïï ^N-C-S-CH -CH H C-H C-H c/ 3

2

3

2

2

2

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch003

Diuron

3

2

(Stauffer. 1959)

Cl

Atrazine {OuPonl, 1954)

ci Ν

DSMA

HC H C3

:CH-NH

CH -Às(0Na) 3

NH-CH -CH 2

Ν

3

0

Ν

(Geigy. 1958)

2

(Ansul. 1956)

Paraquat

Chloramben

2+ N-CH

H C-N

ci

3

3

^~~^-C00H NH Cl

3

(ICI. 1965)

2

(Amchem. 1958)

Linuron

V N H - C - N 0CH3 CI (Hoechst. 1960)

Figure 3. Selected U.S. herbicides introduced into agriculturecompany and year of introduction for each in parentheses

2X-

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch003

46

PESTICIDE CHEMISTRY IN THE 20TH CENTURY

as a l f a l f a , c e r t a i n b e a n s , p o t a t o e s , a n d s w e e t potatoes. I n a d d i t i o n t o c o n t r o l l i n g numerous grass and b r o a d l e a f w e e d s , i t ' c o n t r o l s n u t s e d g e , one o f t h e world's worst weeds. DSMA w a s i n t r o d u c e d b y A n s u l i n 1 9 5 6 ( F i g . 3 ) . DSMA i s a n o r g a n i c a r s e n i c a l h a v i n g c o n t a c t , p o s t emergence a c t i v i t y . I t was f i r s t u t i l i z e d f o r c r a b grass control i n turf. I t i s an e f f e c t i v e h e r b i c i d e i n c o t t o n and i n c i t r u s t r e e s , b u t must be used as a d i r e c t e d spray to avoid contact with the crop foliage. A t r a z i n e was i n t r o d u c e d by G e i g y i n 1958 ( F i g . 3 ) . I t i s a member o f a l a r g e g r o u p o f s y m m e t r i c a l triazine herbicides. A t r a z i n e i s a preemergence h e r b i c i d e to w h i c h c o r n i s t o l e r a n t . I t i s t h e number one h e r b i c i d e i n acreage t r e a t e d and i n d o l l a r s of s a l e s in the United States. The compound i s a l s o used i n o r c h a r d s , p i n e a p p l e , sorghum, and sugarcane. Chloramben, a benzoic acid d e r i v a t i v e introduced by Amchem i n 1 9 5 8 , i s a s e l e c t i v e p r e e m e r g e n c e h e r b i ­ cide ( F i g . 3 ) . I t i s used p r i n c i p a l l y i n soybeans, corn, and peanuts. Paraquat, a b i p y r i d y l q u a t e r n a r y ammonium s a l t , was i n t r o d u c e d by I C I i n 1965 ( F i g . 3 ) . I t i s a non­ s e l e c t i v e , c o n t a c t h e r b i c i d e on p l a n t f o l i a g e , b u t i s immediately i n a c t i v a t e d when a p p l i e d t o s o i l . I t i s used i n minimum t i l l a g e programs and as a p o s t e m e r gence d i r e c t e d spray i n sugarcane and i n f r u i t tree crops. L i n u r o n , a s u b s t i t u t e d urea i n t r o d u c e d by Hoechst in 1960, i s employed p r i m a r i l y as a preemergence h e r b i c i d e ; b u t i ta l s o h a s c o n t a c t e f f e c t on f o l i a g e (Fig. 3 ) . Linuron i s used p r i n c i p a l l y i n soybeans, c o r n , sorghum, wheat, and p o t a t o e s . I t i s often m i x e d w i t h o t h e r h e r b i c i d e s t o b r o a d e n t h e weed spectrum. B r o m a c i l i s a u r a c i l h e r b i c i d e i n t r o d u c e d by du P o n t i n 1 9 6 3 ( F i g . 4 ) . I t c o n t r o l s a b r o a d s p e c t r u m o f weeds i n c i t r u s and p i n e a p p l e c r o p s . The chemical i s a l s o used f o rgeneral v e g e t a t i o n c o n t r o l on n o n c r o p a r e a s s u c h a s r a i l r o a d s a n d i n d u s t r i a l areas. Picloram i s a picolinic acid derivative intro­ d u c e d b y Dow C h e m i c a l i n 1963 ( F i g . 4 ) . P i c l o r a m i s h i g h l y a c t i v e on most p e r e n n i a l b r o a d l e a f and woody s p e c i e s , and most g r a s s e s a r e r e s i s t a n t .

American

ALDER ET AL.

Herbicide

Industry

Picloram

Bromacil

NH

c=o

H C-C;

c

'y^t

C

,

v

3

I .N-ÇH-CH2-CH3 CH

2

c i

^ N

C

0

0

H

(Dow. 1963)

3

(DuPont. 1963)

Fluometuron

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch003

Trifluralin H C-H2C-H2Cv /CH2-CH2-CH 3

N

3

CH CF

3

3

(CIBA. 1964)

CF

3

(Lilly. 1963)

Bentazon Alachlor 0

CH2-CH3

CrVO-Cr^

\==/ CH2-CH3

(BASF, 1973)

(Monsanto. 1969)

Glyphosate

Metribuzin SCH

3

HOOC-CH2-NH-CH2- P(0H)

2

N-NH2

H C—C—CH 3

CH

(Monsanto, 1974)

3

3

(Bayer. 1971)

Figure 4. Selected U.S. herbicides introduced into agriculturecompany and year of introduction for each in parentheses

American Chemical Society Library

1155 16th St. N. w.

Washington, D. C. 20031

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch003

48

PESTICIDE CHEMISTRY IN THE

20TH CENTURY

T r i f l u r a l i n i s a d i n i t r o a n i l i n e and was intro­ d u c e d by E l i L i l l y i n 1963 (Fig. 4). I t was the f i r s t of a number of s i m i l a r d i n i t r o a n i l i n e s . It is widely u s e d i n c o t t o n and s o y b e a n s and is labeled for u s e o n m o r e t h a n 50 c r o p s . It is usually incorporated i n t o the s o i l p r i o r to p l a n t i n g the crop. Fluometuron i s another substituted urea intro­ d u c e d by C I B A i n 1964 (Fig. 4). I t i s a preemergence h e r b i c i d e and finds i t s niche primarily in cotton and sugarcane. It i s usually applied in combination with o t h e r h e r b i c i d e s to b r o a d e n t h e s p e c t r u m of weed species controlled. A l a c h l o r i s an a c e t a n i l i d e i n t r o d u c e d by Monsanto i n 1969 (Fig. 4). Al,achlor i s a preemergence h e r b i ­ c i d e , e x t e n s i v e l y used p r i m a r i l y i n corn, soybeans, and peanuts. Bentazon i s a benzothiadiazine introduced by BASF i n 1973 (Fig. 4). It i s a contact herbicide for s e l e c t i v e p o s t e m e r g e n c e c o n t r o l o f many broadleaf weeds i n s o y b e a n s , r i c e , c o r n , and peanuts. Metribuzin i s an a s y m m e t r i c a l t r i a z i n e intro­ d u c e d by B a y e r i n 1971 (Fig. 4). Metribuzin i s used a l o n e or i n c o m b i n a t i o n w i t h o t h e r h e r b i c i d e s i n soy­ b e a n s , s u g a r c a n e , and potatoes. Glyphosate i s a substituted glycine introduced by M o n s a n t o i n 1974 (Fig. 4). It is nonselective and when a p p l i e d t o p l a n t f o l i a g e , c o n t r o l s b o t h a n n u a l and p e r e n n i a l b r o a d l e a v e d weeds and grasses. The United S t a t e s has been a l e a d e r i n the d e v e l o p m e n t and use of h e r b i c i d e s . In 1951, herbi­ c i d e s a m o u n t e d t o o n l y 1 0 % o f t h e t o t a l o f 463 million pounds of p e s t i c i d e s p r o d u c e d i n t h i s c o u n t r y ( F i g . 5 ) . I n 1974, the l a t e s t year f o r which r e c o r d s are avail­ a b l e , 604 m i l l i o n p o u n d s , o r 4 3 % o f t h e 1,417 million pounds of p e s t i c i d e s p r o d u c e d i n the U n i t e d States, were h e r b i c i d e s (_5) . Moving to p e s t i c i d e s a l e s , i n m i l l i o n s of d o l l a r s at the manufacturer's l e v e l , there i s even greater growth ( F i g . 6). Herbicides have c o n s i s t e n t l y been more v a l u a b l e per pound than most o t h e r p e s t i c i d e s (5.). In 1951, herbicides c o n s t i t u t e d 13% of the d o l l a r s s p e n t f o r p e s t i c i d e s and i n 1974 herbicide s a l e s had grown t o 58%. I n 23 y e a r s h e r b i c i d e sales d o l l a r s had grown n e a r l y f i f t y f o l d , to over one b i l l i o n d o l l a r s per year. The leadership o f t h e U.S. herbicide industry is e v i d e n c e d by t h e f a c t t h a t , i n 1974, o v e r 58% of the worldwide expenditures f o r h e r b i c i d e s were i n the U.S. (6).

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch003

3. ALDER ET AL. American Herbicide Industry

49

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch003

50

PESTICIDE CHEMISTRY IN THE 20TH CENTURY

F i g u r e 7 s h o w s t h e t o t a l a c r e s o f U.S. cropland and t h o s e t r e a t e d w i t h h e r b i c i d e s . Those acres planted to crops (not to pastures, f o r e s t s , etc.) i n 1959 w e r e 359 m i l l i o n a c r e s , a n d i n 1 9 7 4 , 368 m i l l i o n acres. The a c r e s t r e a t e d w i t h h e r b i c i d e s h a v e i n ­ c r e a s e d f r o m 53 m i l l i o n i n 1 9 5 9 t o a n e s t i m a t e d 185 m i l l i o n i n 1974, or from l e s s than 15% of t h e a c r e s p l a n t e d i n 1 9 5 9 t o o v e r 5 0 % i n 1 9 7 4 (7_, 8, 9, 10). There has been r a p i d growth i n usage of p r e ­ e m e r g e n c e h e r b i c i d e s ( F i g . 8 ) (JB, 9^, 10). Pre­ emergence h e r b i c i d e s a r e a p p l i e d t o the s o i l prior to g e r m i n a t i o n of weeds and c r o p s . Postemergence a p p l i c a t i o n s are a p p l i e d t o e s t a b l i s h e d weeds, such a s t h e u s e o f 2,4-D on w e e d s g r o w i n g i n c o r n o r w h e a t . I n 1959, most h e r b i c i d e a p p l i c a t i o n s were postemergence. P r e e m e r g e n c e t r e a t m e n t s have grown rapidly since that time. I n 1968, o n l y 45% of the h e r b i c i d e t r e a t m e n t s were p r e e m e r g e n c e ; b u t by 1 9 7 1 , 68%; and i n 1974, 70% of t h e a c r e s t r e a t e d w i t h h e r b i c i d e s employed preemergence treatments. H o w e v e r , some o f the newer postemergence m a t e r i a l s b e i n g developed f o r t h e c o n t r o l o f t o l e r a n t a n d r e s i s t a n t w e e d s may slow t h i s t r e n d , on a p e r c e n t a g e b a s i s , toward preemergence t r e a t m e n t s. The c h e m i c a l i n d u s t r y h a s s u p p o r t e d h e r b i c i d e r e s e a r c h i n t e r m s of b o t h s c i e n t i s t s and r e s o u r c e s . E s t i m a t e s of the numbers of h e r b i c i d e r e s e a r c h workers i n i n d u s t r y i n the United States adapted from i n f o r m a t i o n p r o v i d e d i n t h e l a s t two s u r v e y s o f t h e National A g r i c u l t u r a l Chemicals Association are pre­ s e n t e d i n F i g u r e 9 ( J L l , 1_2) . In 1971, t h e r e were 827 i n d u s t r y s c i e n t i s t s i n h e r b i c i d e r e s e a r c h a n d d e v e l o p m e n t — 3 1 9 P h . D . ' s , 183 M . S . ' s , a n d 325 B . S . ' s . S u p p o r t i n g t h e s e s c i e n t i s t s w e r e 495 o t h e r people s e r v i n g p r i m a r i l y as t e c h n i c i a n s . The n u m b e r s have c o n t i n u e d t o i n c r e a s e u n t i l i n 1975, t h e r e were 451 P h . D . ' s , 247 M a s t e r s , 404 B a c h e l o r s , w i t h 877 i n t h e " o t h e r " c a t e g o r y , f o r a t o t a l o f n e a r l y 2,000 people working i n industry h e r b i c i d e research i n the United States. We w o u l d f u r t h e r e s t i m a t e t h a t o f t h i s number a t l e a s t h a l f a r e c h e m i s t s - - o r g a n i c , physical, a n a l y t i c a l , and b i o c h e m i s t s . The r e m a i n i n g h a l f a r e b i o l o g i s t s and s c i e n t i s t s w i t h v a r i o u s agricultural backgrounds. F i g u r e 10 s h o w s e s t i m a t e s o f t h e e x p e n d i t u r e s by U.S. i n d u s t r y on r e s e a r c h and d e v e l o p m e n t o f h e r b i ­ c i d e s ( J J _ , 12). I n 1971, 46. 3 m i l l i o n d o l l a r s was spent. I n f o u r y e a r s e x p e n d i t u r e s had i n c r e a s e d 80% to 83.3 m i l l i o n dollars.

3.

ALDER ET AL.

American

Herbicide

I

51

Industry

I U.S. CROPLAND ACREAGE

• i

'59

HERBICIDE TREATED ACRES

62

'65

'68

71

74

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch003

YEAR Figure 7.

Herbicide usage on U.S. croplands

Figure 8.

Figure 9.

Herbicide-treated acres

Herbicide research workers in industry (estimated)

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch003

PESTICIDE CHEMISTRY IN THE 20TH CENTURY

Figure 11.

Projected U.S. herbicide market by product groups

3.

American

ALDER E T A L .

Herbicide

53

Industry

W h a t d o we s e e i n t h e n e a r f u t u r e f o r h e r b i c i d e s ? L o o k i n g a h e a d f i v e g r o w i n g s e a s o n s t o 1 9 8 0 , we s e e p r e d i c t i o n s of continued growth i n h e r b i c i d e sales and i n r e s e a r c h and d e v e l o p m e n t .

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch003

The

TrCLKm Ck&msLcalA

publication

recently

projected

growth o f t h e h e r b i c i d e market by p r o d u c t group (6) ( F i g . 1 1 ) . I n 1 9 7 4 , t h e f i r s t c o l u m n , we f i n d a r s e n i c a l s w i t h 1% o f t h e m a r k e t ; p h e n o x i e s w i t h 4 . 7 % ; p h e n y l u r e a s such as d i u r o n , l i n u r o n , and f l u o m e t u r o n w i t h 6.6%; b e n z o i c s s u c h a s c h l o r a m b e n , d i c a m b a , t r i c h l o r o b e n z o i c a c i d w i t h 9.5%; c a r b a m a t e s s u c h as EPTC, d i a l l a t e , and chloropropham w i t h 10.2%; and t h e t r i a z i n e s such as a t r a z i n e , prometryne, and cyanazine w i t h 29.7%. The " o t h e r s " c a t e g o r y w i t h 3 8 . 3 % i n c l u d e s a l a c h l o r , p a r a q u a t , t r i f l u r a l i n , a n d some o f t h e m o r e recent product e n t r i e s such as bentazon, g l y p h o s a t e , and m e t r i b u z i n . The s e c o n d c o l u m n d e p i c t s t h e 1 9 8 0 h e r b i c i d e market as compared w i t h 1974, w i t h a 44% growth i n ­ crease overall. A l l p r o d u c t g r o u p s show some real growth, even though p e r c e n t o f t h e t o t a l market d e ­ clines i n a l l e x c e p t t h e " o t h e r s " c a t e g o r y . The " o t h e r s " c a t e g o r y w i l l show a n a c t u a l i n c r e a s e o f 7 2 % and i n c r e a s e i t s p e r c e n t a g e s h a r e o f t h e m a r k e t from 38.3 i n 1 9 7 4 t o 4 5 . 8 % i n 1 9 8 0 . If r e s e a r c h and development expenses and i n d u s t r y s t a f f i n g c o n t i n u e t o grow a t t h e r a t e o f t h e l a s t five years, the expenditures f o r industry herbicide r e s e a r c h and development can be p r o j e c t e d t o double from 1975 t o 1980, r e a c h i n g 173 m i l l i o n d o l l a r s i n 1980 (Table I I I ) . I f i n d u s t r y p e r s o n n e l needs con­ t i n u e t o i n c r e a s e d u r i n g t h e next f i v e y e a r s a tt h e same r a t e a s i n t h e p a s t f i v e , t h e r e w i l l b e 1 , 5 0 0 s c i e n t i f i c a n d 1,800 s u p p o r t p e r s o n n e l r e q u i r e d b y i n d u s t r y i n 1980, o r an i n c r e a s e o f67%. Table

I I I .

Herbicide

1975 $83,300

R & D

projections

EXPENDITURES (000 s) f

1980 $173,500

PERSONNEL

1,102 877

SCIENTIFIC SUPPORT

1,500 1,800

1,979

TOTAL

3,300

54

PESTICIDE

C H E M I S T R Y IN T H E 20TH C E N T U R Y

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch003

W i t h a l l t h e w o r k t h a t h a s g o n e o n t h e l a s t 30 y e a r s , and w i t h o v e r 130 h e r b i c i d e s i n u s e t o d a y , a r e a l l t h e weed p r o b l e m s s o l v e d ? Not at a l l . Old p r o b l e m s a b o u n d a n d new p r o b l e m s a r i s e e a c h year. T h e r e a r e many o p p o r t u n i t i e s f o r new d e v e l o p m e n t s i n h e r b i c i d a l weed c o n t r o l . Some a r e : 1.

Further development of h e r b i c i d e s with true p h y s i o l o g i c a l tolerance t o s p e c i f i c crop plants s u c h as i s e x h i b i t e d by a t r a z i n e on c o r n .

2.

B e t t e r combinations of h e r b i c i d e s a r e needed t o p r o v i d e t h e b r o a d s p e c t r u m o f weed c o n t r o l n e e d e d in different localities.

3.

The c o n t r o l o f p e r s i s t e n c e needs f u r t h e r c o n ­ sideration. A t t i m e s o n l y two o r t h r e e h o u r s o r two o r t h r e e d a y s o f h e r b i c i d e a c t i v i t y a r e desired. F o r many c r o p s a p e r s i s t e n c e o f t w o or t h r e e months i s needed; whereas i n c e r t a i n c o n d i t i o n s , as f o r s o i l s t e r i l a n t s and v a r i o u s t r e e c r o p s , two o r t h r e e y e a r s o f p e r s i s t e n c e may b e d e s i r e d . Through inherent compound c h a r a c t e r i s t i c s , t h r o u g h t h e amount a p p l i e d , a n d t h r o u g h i m p r o v e d f o r m u l a t i o n s , we c a n a n d must t a i l o r p e r s i s t e n c e o f h e r b i c i d e s t o f i t t h e p e r i o d o f weed c o n t r o l d e s i r e d .

4.

New a n d b e t t e r a q u a t i c h e r b i c i d e s , i n c l u d i n g a q u a t i c weed g r o w t h r e g u l a t o r s , a r e needed since a q u a t i c weeds a r e n o t w e l l c o n t r o l l e d a t p r e s e n t . We m u s t l e a r n h o w t o c o n t r o l w e e d s i n r u n n i n g water and i n waterways, as w e l l as l a k e s and ponds.

5.

The t r a n s f o r m a t i o n o f v a l u e l e s s b r u s h l a n d s t o productive pasture lands by t h e use of h e r b i c i d e s holds tremendous p o t e n t i a l f o r increased beef product ion.

6.

The u s e o f a n t i d o t e c h e m i c a l s or " a n t i - h e r b i c i d e s " on c r o p s t o c o u n t e r a c t the effect of herbicides and t h e r e b y increase crop tolerance i s a h i g h l y promising procedure. This technique i s already b e i n g u s e d i n o n e s e r i e s o f c o m p o u n d s a n d may e n j o y g r e a t e r a c c e p t a n c e as more " a n t i - h e r b i c i d e s " become a v a i l a b l e .

7.

D i f f e r e n c e s i n crop v a r i e t y t o l e r a n c e have been known f o r a l o n g t i m e . Thus, there e x i s t s t h e

3.

ALDER ET A L .

American

Herbicide

Industry

55

p o s s i b i l i t y of developing, through s e l e c t i v e breeding, c r o p s t h a t a r e more r e s i s t a n t t o herbicides.

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch003

8.

The u s e o f growth r e g u l a t o r s t o s e v e r e l y inhibit w e e d s may p r o v e o f v a l u e . I n many c a s e s i t i s not r e a l l y n e c e s s a r y t o k i l l t h e weed. I t i s u s u a l l y adequate t o i n h i b i t i tso that i t i s unable t o compete s u c c e s s f u l l y o r t o reproduce.

The future of herbicides remains promising. New and b e t t e r compounds w i t h g r e a t e r s a f e t y t o c r o p s , t o man, and t h e e n v i r o n m e n t w i l l become a v a i l a b l e . I f the i n c r e a s e d food needs of t h e world a r e met, they w i l l be met a n d man's l a b o r b u r d e n e a s e d , i n p a r t , b y the u s e o f s u i t a b l e h e r b i c i d a l compounds.

Literature 1. 2. 3.

Cited

Hay, J. R. Weed S c i e n c e (1974) 22:439-442. Shaw, W. C. Weeds (1964) 12:153-162. Knake, E. L. and Slife, F. W. Weeds (1962) 10:26-29. 4. Timmons, F. L. Weed S c i e n c e (1970) 18:294-307. 5. U.S. Tariff Commission. S y n t h e t i c O r g a n i c C h e m i c a l s , U n i t e d S t a t e s P r o d u c t i o n and S a l e s of Pesticides and R e l a t e d P r o d u c t s , A n n u a l R e p o r t s for 1951-1974. 6. "World Pesticide M a r k e t s - - F C Special R e p o r t " Farm C h e m i c a l s (1975) 138(9):45-48. 7. "Agricultural Statistics" U.S.D.A., Editions 1959-1974. 8. " E x t e n t and Cost of Weed C o n t r o l w i t h H e r b i c i d e s and an E v a l u a t i o n of Important Weeds, 1965" Agr. R e s . S e r v i c e , U.S.D.A., Economic R e s . Service, Report ARS 3 4 - 1 0 2 , 1968. 9. " E x t e n t and Cost of Weed C o n t r o l w i t h H e r b i c i d e s and an E v a l u a t i o n of Important Weeds, 1968" Agr. R e s . S e r v i c e , U.S.D.A., Economic R e s . Service, Report A R S - H - 1 , 1972. 10. " F a r m e r s ' Use of Pesticides in 1971" U.S.D.A., Economic R e s . S e r v i c e , Agricultural Economic Report 252, 1974. 11. "Industry Profile S t u d y , 1973" N a t i o n a l Agricultural Chemicals Association, Washington, D.C. 12. "Industry Profile S t u d y , 1975" N a t i o n a l Agricultural Chemicals Association, Washington, D.C.

4 Mode of Action of Herbicides D O N A L D E. M O R E L A N D

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch004

U. S. Department of Agriculture, Agricultural Research Service Crop Science Department, North Carolina State University, Raleigh, N . C . 27607

The primary biochemical sites of action of some herbicides have been i d e n t i f i e d and an appreciation i s being gained on how these same herbicides express phytotoxicity by i n t e r f e r i n g with the plant's biochemistry. The progress being made in this area of research accompanies the increased comprehension that i s be­ ing achieved on the basic biochemistry of plant growth and on the endogenous control systems that regulate growth and development. Corbett (1) recently summarized the current status of b i o ­ chemical knowledge on the mode of action of herbicides in the general form shown i n Figure 1. Interference with the processes i d e n t i f i e d in the left-hand column has been documented for the action of one or more herbicides (1, 2, 3, 4 ) . Interferences are indicated as affecting various interrelated processes (structural organization, energy supply, and growth and reproduction). I f the interference i s extreme, the treated plant dies. Thiolcarbamates have been shown to interfere with lipid syn­ thesis and, thereby, to a l t e r the i n t e g r i t y of membranes. Some of the pyridazinones interfere not only with lipid synthesis, but also with the Hill reaction and carotenoid synthesis. The bipy­ ridiliums intercept photoinduced electron flow i n the chloroplasts and undergo one-electron reduction to form free r a d i c a l s . When the radicals are oxidized, hydrogen peroxide i s formed, which i s thought to react with unsaturated membrane lipids. Membrane per­ meability i s increased and, subsequently, c e l l u l a r structure i s destroyed. Mitochondrial electron transport and oxidative phos­ phorylation are affected by a large group of herbicides, including the N-phenylcarbamates, a c y l a n i l i d e s , phenols, and halogenated b e n z o n i t r i l e s . Most of the herbicides that interfere with the mitochondrial reactions also i n h i b i t photosynthetic electron transport as do the phenylureas, s - t r i a z i n e s , and u r a c i l s . The N-phenylcarbamates and d i n i t r o a n i l i n e s , in addition to affecting the mitochondrial and chloroplast reactions, arrest cell d i v i s i o n . Glyphosate has been reported to interfere with protein synthesis 56

4.

MORELAND

Action

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Herbicides

57

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch004

i n Lerrma (5) . I d e n t i f i c a t i o n o f t h e b i o c h e m i c a l mechanisms i n v o l v e d i n t h e a c t i o n of the phenoxies continues t o challenge i n v e s t i g a t o r s . These h e r b i c i d e s a r e d e p i c t e d , i n F i g u r e 1 , as a f f e c t i n g t h e un­ known s i t e a t w h i c h t h e n a t i v e hormone, i n d o l e a c e t i c a c i d , e x ­ presses i t s growth-controlling a c t i o n ( 1 ) . Of t h e v a r i o u s b i o c h e m i c a l p a t h w a y s i d e n t i f i e d as b e i n g a f f e c t e d by h e r b i c i d e s , the c h l o r o p l a s t - m e d i a t e d r e a c t i o n s have r e c e i v e d t h e g r e a t e s t a t t e n t i o n . A p p r o x i m a t e l y 70 p e r c e n t o f t h e c u r r e n t c o m m e r c i a l h e r b i c i d e s , w h i l e t h e y may a l s o a f f e c t o t h e r systems, i n t e r f e r e w i t h c h l o r o p l a s t r e a c t i o n s . Hence, the o b j e c ­ t i v e s o f t h i s p a p e r a r e t o r e v i e w some o f t h e w o r k c o n d u c t e d w i t h i s o l a t e d c h l o r o p l a s t s , e v a l u a t e the s t a t u s o f these s t u d i e s , and r e l a t e the observed i n t e r f e r e n c e s t o the expression o f p h y t o t o x i city. Chloroplas t-mediated

Reactions.

I n t e r f e r e n c e by c e r t a i n p h e n y l u r e a and #-phenylcarbamate h e r b i c i d e s with the photochemical reactions o f i s o l a t e d c h l o r o ­ p l a s t s was f i r s t r e p o r t e d i n 1956 ( 2 ) . O v e r t h e n e x t few y e a r s , i n h i b i t i o n by t h e s - t r i a z i n e s , u r a c i l s , b e n z i m i d a z o l e s , and benz o n i t r i l e s was r e p o r t e d (2^, _3, 6) . C h l o r o p l a s t s o f h i g h e r p l a n t s a r e s a u c e r - s h a p e d , and f r o m 4 t o 10 y m i n d i a m e t e r and 1 t o 3 ym t h i c k . The c h l o r o p h y l l i s concentrated i n bodies w i t h i n the c h l o r o p l a s t s c a l l e d grana, w h i c h a r e a b o u t 0.4 ym i n d i a m e t e r . Under t h e e l e c t r o n m i c r o ­ scope, t h e grana appear as h i g h l y o r g a n i z e d , p r e c i s e l y s t a c k e d l a m e l l a e , t o w h i c h t h e c h l o r o p h y l l i s b o u n d , imbedded i n a s t r o m a matrix. The l i g h t a n d a s s o c i a t e d e l e c t r o n t r a n s p o r t r e a c t i o n s t a k e p l a c e i n t h e l a m e l l a e , w h e r e a s enzymes i n v o l v e d i n c a r b o n d i o x i d e f i x a t i o n a r e l o c a t e d i n the stroma. P h o t o i n d u c e d e l e c t r o n t r a n s p o r t and the c o u p l e d p h o s p h o r y l a ­ t i o n r e a c t i o n s as they a r e p o s t u l a t e d t o o c c u r i n c h l o r o p l a s t s a r e p r e s e n t e d s c h e m a t i c a l l y i n F i g u r e 2. N o t a l l i n v e s t i g a t o r s a g r e e o n t h e d e t a i l s o f t h i s scheme, a n d some e v e n q u e s t i o n t h e sequence o f t h e i n t e r m e d i a t e s . The numbers a n d l o c a t i o n s o f t h e p h o s p h o r y l a t i o n s i t e s a l s o remain t o be i d e n t i f i e d p r e c i s e l y . However, t h e scheme i s a r e a s o n a b l e a p p r o x i m a t i o n b a s e d o n a v a i l ­ able information. Reactions that occur i n the l i g h t a r e r e p r e ­ s e n t e d b y t h e o p e n arrows, a n d t h e s o l i d a r r o w s r e p r e s e n t e l e c t r o n t r a n s f e r s t h a t occur i n the dark. Through a s e r i e s o f o x i d a t i o n - r e d u c t i o n r e a c t i o n s d r i v e n by two l i g h t r e a c t i o n s o p e r a t i n g i n s e r i e s a n d i n v o l v i n g s e v e r a l h u n d r e d c h l o r o p h y l l m o l e c u l e s , e l e c t r o n s f l o w f r o m w a t e r t o NADP. P a r t i c i p a t i n g i n t h e o v e r a l l r e a c t i o n i s a w a t e r - s p l i t t i n g com­ p l e x t h a t i n c l u d e s a m a n g a n o - p r o t e i n a n d c h l o r i d e i o n s . An un­ i d e n t i f i e d c h l o r o p h y l l α molecule serves as the r e a c t i o n center o f p h o t o s y s t e m I I , w i t h Q as t h e p r i m a r y e l e c t r o n a c c e p t o r . I n ­ v o l v e d s e q u e n t i a l l y on the e l e c t r o n t r a n s p o r t c h a i n a r e p l a s t o -

PHOSPHORYLATION

ELECTRON TRANSPORT

AT

Figure 1.

COMBINATION

SITE

—

GROWTH AND REPRODUCTION

ENERGY SUPPLY

Summary diagram of the mode of action of pesticides [adapted from Corbett (1)]

IAA

DIVERTED

DESTRUCTION OF PIGMENTS

SYNTHESIS

RNA,

DNA,

PROTEIN

OR NUCLEAR DIVISION

SYNTHESIS—>

CELL

CAROTENOID

PHOTOSYNTHETIC ELECTRON TRANSPORT ( H I L L REACTION)

OXIDATIVE

MITOCHONDRIAL

ELECTRON TRANSPORT

INTEGRITY-

PHOTOSYNTHETIC

MEMBRANE

\

STRUCTURAL ORGANIZATION

SYNTHESIS—

LIPID

MODIFIED

FUNCTION

INTERFERENCE WITH

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch004

DEATH

or

M to Ο

w

ο

M

00

4.

MORELAND

Action of

59

Herbicides

-0.6 r-

-0.4 NADP+

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch004

-0.2

Ô

ο

•0.2

+0.4 χ ο ο

UJ

* +0.6

+0.8

Figure 2. Schematic of photoinduced electron transport and phosphorylation reactions considered to occur in chloroplast lamellae [from Moreland and Hilton (2)]. Open arrows indicate light reactions; solid arrows indicate dark reactions; and the narrow dashed line represents the cyclic pathway. Abbreviations used: PS J, photosystem I; PS 11, photosystem 11; Ύ, postulated electron donor for photosystem 11; Q, unknown primary electron acceptor for photosystem 11; PQ, plastoquinones; cyt b, b-type cyto­ chromes; cyt f, cytochrome f; P C , plastocyanin; P , reaction center chlorophyll of photosystem 1; F R S , ferredoxin-reducing substance; Fd, ferredoxin; Fp, ferreaoxinNADP oxidoreductase; FeCy, ferricyanide; asc, ascorbate; and DPIP, 2,6-dichlorophenolindophenol. The numbers la, lb, 2, 3, and 4 indicate postulated sites of action by herbicides. See text for details. 70fl

PESTICIDE C H E M I S T R Y IN

60

THE

20TH C E N T U R Y

q u i n o n e , a b-type c y t o c h r o m e , c y t o c h r o m e / ( a
Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch004

a

C l a s s i f i c a t i o n of I n h i b i t o r y Herbicides. H e r b i c i d e s t h a t i n h i b i t the p h o t o c h e m i c a l r e a c t i o n s o f i s o l a t e d c h l o r o p l a s t s have been c a l l e d r o u t i n e l y i n h i b i t o r s of t h e H i l l r e a c t i o n . T h i s has b e e n done p r i m a r i l y f o r c o n v e n i e n c e and b e c a u s e , f o r many y e a r s , t h e i r a c t i o n was e v a l u a t e d u n d e r n o n p h o s p h o r y l a t i n g c o n d i t i o n s , f r e q u e n t l y w i t h f e r r i c y a n i d e as the e l e c t r o n a c c e p t o r . I n t h e p a s t few y e a r s , more s o p h i s t i c a t e d s t u d i e s h a v e b e e n c o n d u c t e d w i t h h e r b i c i d e s and more i s known about t h e i r d i f f e r e n t i a l a c t i o n s . C o n s e q u e n t l y , M o r e l a n d and H i l t o n (2) s e p a r a t e d h e r b i c i d a l i n h i b i t o r s o f the photochemically i n d u c e d r e a c t i o n s i n t o the f o l l o w i n g c l a s s e s : (a) e l e c t r o n t r a n s ­ p o r t i n h i b i t o r s , (b) u n c o u p l e r s , ( c ) e n e r g y t r a n s f e r i n h i b i t o r s , (d) i n h i b i t o r y u n c o u p l e r s ( m u l t i p l e t y p e s o f i n h i b i t i o n ) , and (e) e l e c t r o n a c c e p t o r s . A f u l l comprehension o f the s p e c i f i c s i t e s i n v o l v e d i n the i n h i b i t o r y a c t i o n o f h e r b i c i d e s and t h e mechanisms t h r o u g h w h i c h i n h i b i t i o n i s p r o d u c e d w i l l b e a c h i e v e d o n l y when t h e u n c e r t a i n ­ t i e s a s s o c i a t e d w i t h t h e s e q u e n c e and i n t e r r e l a t i o n o f components i n the e l e c t r o n t r a n s p o r t p a t h w a y , t h e numbers and l o c a t i o n s o f p h o s p h o r y l a t i o n s i t e s , and the mechanism o f p h o s p h o r y l a t i o n h a v e been r e s o l v e d . Electron Transport I n h i b i t o r s . Electron transport i s i n ­ h i b i t e d when one o r more o f t h e i n t e r m e d i a t e e l e c t r o n t r a n s p o r t c a r r i e r s are r e m o v e d o r i n a c t i v a t e d . The s i t e o f a c t i o n o f most h e r b i c i d a l e l e c t r o n t r a n s p o r t i n h i b i t o r s i s c o n s i d e r e d t o be associated c l o s e l y with photosystem I I . Consequently, reactions c o u p l e d t o p h o t o s y s t e m I I a r e i n h i b i t e d , s u c h as b a s a l e l e c t r o n

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t r a n s p o r t , me t h y l a m i n e - u n c o u p l e d e l e c t r o n t r a n s p o r t , and n o n c y c l i c e l e c t r o n t r a n s p o r t w i t h w a t e r as e l e c t r o n donor and f e r r i ­ c y a n i d e o r NADP as e l e c t r o n a c c e p t o r . The c o u p l e d p h o s p h o r y l a ­ t i o n i s i n h i b i t e d by t h e a c t i o n o n t h e r e d u c t i v e r e a c t i o n . P a r t i a l r e a c t i o n s n o t d e p e n d e n t on p h o t o s y s t e m I I , s u c h as c y c l i c p h o s p h o r y l a t i o n o r t h e p h o t o r e d u c t i o n o f NADP w i t h an e l e c t r o n donor t h a t circumvents photosystem I I ( a s c o r b a t e + DPIP), are e i t h e r not i n h i b i t e d or i n h i b i t e d only weakly. These h e r b i c i d e s a l s o do n o t i n h i b i t m i t o c h o n d r i a l o x i d a t i v e p h o s p h o r y l a t i o n . The a c t i o n o f d i u r o n has b e e n s t u d i e d more i n t e n s i v e l y and e x t e n s i v e l y t h a n t h a t o f any o t h e r h e r b i c i d e . However, i t s s i t e o f i n h i b i t i o n has n o t b e e n i d e n t i f i e d t o the s a t i s f a c t i o n o f a l l investigators. I n 1962, Duysens and Ames ζ (_7) p r o v i d e d e v i d e n c e t h a t d i u r o n a c t e d on the r e d u c i n g s i d e o f p h o t o s y s t e m I I b e t w e e n Q and p l a s t o q u i n o n e ( F i g u r e 2, s i t e l a ) . However, o t h e r i n v e s t i ­ g a t o r s h a v e s u g g e s t e d t h a t d i u r o n may a c t o n t h e o x i d i z i n g s i d e o f p h o t o s y s t e m I I ( F i g u r e 2, s i t e l b ) , o r d i r e c t l y o n t h e c h l o r o ­ p h y l l a r e a c t i o n c e n t e r o f p h o t o s y s t e m I I ( 2 ) . R e c e n t l y , Renger (8) p r o p o s e d t h a t d i u r o n may a c t on b o t h s i d e s o f p h o t o s y s t e m I I : (a) on t h e r e d u c i n g s i d e w h e r e i t a c t s as an i n h i b i t o r , and (b) on t h e o x i d i z i n g s i d e w h e r e i t a c c e l e r a t e s t h e d e a c t i v a t i o n o f the w a t e r - s p l i t t i n g enzyme s y s t e m Y. The a c t i o n o f many o t h e r d i v e r s e l y s t r u c t u r e d compounds i s compared f r e q u e n t l y t o t h a t o f d i u r o n ; h o w e v e r , t h e i r s i t e ( s ) o f a c t i o n has n o t b e e n r e s o l v e d b e y o n d t h e g e n e r a l a r e a a r o u n d p h o t o s y s t e m I I . The mechanism t h r o u g h w h i c h i n h i b i t i o n i s i m p o s e d , even by d i u r o n , i s unknown. H e r b i c i d e s t h a t seem t o h a v e a s i n g l e s i t e o f a c t i o n on t h e p h o t o c h e m i c a l pathway, w h i c h i s a s s o c i a t e d c l o s e l y w i t h photo­ s y s t e m I I , a r e t h e c h l o r i n a t e d p h e n y l u r e a s , fr£ s - c a r b a m a t e s s u c h as phenmedipham, c h l o r i n a t e d s - t r i a z i n e s , s u b s t i t u t e d u r a c i l s , pyridazinones, diphenylethers, 1,2,4-triazinones, azido-st r i a z i n e s , cyclopropane-carboxamides, p - a l k y l a n i l i d e s , p - a l k y l t h i o a n i l i d e s , aminotriaζinones, and u r e a - c a r b a m a t e s ( 2 ) . Uncouplers. Uncouplers d i s s o c i a t e e l e c t r o n t r a n s p o r t from photophosphorylation. B o t h n o n c y c l i c and c y c l i c phosphorylation a r e i n h i b i t e d , b u t e l e c t r o n t r a n s p o r t r e a c t i o n s a r e e i t h e r un­ a f f e c t e d or s t i m u l a t e d . Because uncouplers r e l i e v e the i n h i b i ­ t i o n of e l e c t r o n t r a n s p o r t imposed by energy t r a n s f e r i n h i b i t o r s , they are c o n s i d e r e d to a c t a t a s i t e c l o s e r to the e l e c t r o n t r a n s p o r t c h a i n than the s i t e o f phosphate uptake. I n F i g u r e 2, t h e y a r e shown ( s i t e 2) as d i s s i p a t i n g some f o r m o f c o n s e r v e d e n e r g y r e p r e s e n t e d as ^ on t h e n o n c y c l i c and c y c l i c A T P - g e n e r a t i n g pathways. P e r f l u i d o n e i s the o n l y h e r b i c i d e i d e n t i f i e d t o d a t e t h a t f u n c t i o n s as a p u r e u n c o u p l e r a t pH 8.0 ( 2 ) . Com­ pounds t h a t u n c o u p l e p h o t o p h o s p h o r y l a t i o n a l s o u n c o u p l e m i t o ­ chondrial oxidative phosphorylation. Energy Transfer I n h i b i t o r s . Energy t r a n s f e r i n h i b i t o r s act d i r e c t l y on p h o s p h o r y l a t i o n . Like electron transport inhibitors,

62

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t h e y i n h i b i t b o t h e l e c t r o n t r a n s p o r t and p h o s p h o r y l a t i o n in c o u p l e d systems. However, a d d i t i o n o f an a p p r o p r i a t e u n c o u p l e r releases t h e i n h i b i t i o n o f e l e c t r o n f l o w ( b u t n o t o f ATP f o r m a ­ t i o n ) . The 1 , 2 , 3 - t h i a d i a z o l y l - p h e n y l u r e a s have been r e p o r t e d to a c t as e n e r g y t r a n s f e r i n h i b i t o r s i n p h o t o p h o s p h o r y l a t i o n ( 9 ) . N o n h e r b i c i d e s t h a t b e h a v e i n t h i s way a r e the a n t i b i o t i c D i o - 9 and p h l o r i z i n . Energy t r a n s f e r i n h i b i t o r s are d e p i c t e d i n F i g u r e 2 as a f f e c t i n g s i t e 3 on t h e n o n c y c l i c and c y c l i c A T P - g e n e r a t i n g pathways. I n h i b i t o r y uncouplers. I n h i b i t o r y u n c o u p l e r s i n h i b i t the r e a c t i o n s a f f e c t e d by b o t h e l e c t r o n t r a n s p o r t i n h i b i t o r s and un­ couplers. H e n c e , t h e y i n h i b i t b a s a l , m e t h y l a m i n e - u n c o u p l e d , and c o u p l e d e l e c t r o n t r a n s p o r t w i t h f e r r i c y a n i d e as e l e c t r o n a c c e p t o r a n d w a t e r as t h e e l e c t r o n d o n o r , much l i k e e l e c t r o n t r a n s p o r t i n ­ hibitors. Coupled n o n c y c l i c photophosphorylation i s i n h i b i t e d and the p h o s p h o r y l a t i o n r e a c t i o n i s s l i g h t l y more s e n s i t i v e t h a n the r e d u c t i o n o f f e r r i c y a n i d e . C y c l i c p h o t o p h o s p h o r y l a t i o n i s a l s o i n h i b i t e d . NADP r e d u c t i o n , when p h o t o s y s t e m I I i s c i r c u m ­ v e n t e d w i t h a s c o r b a t e + DPIP, i s not i n h i b i t e d ; however, the associated phosphorylation i s i n h i b i t e d . I n h i b i t o r y uncouplers a c t a t b o t h s i t e s 1 and 2 ( F i g u r e 2 ) . H e r b i c i d e s t h a t a c t as i n h i b i t o r y u n c o u p l e r s a r e d i n i t r o phenols, phenylcarbamates, a c y l a n i l i d e s , halogenated benzonit r i l e s , substituted imidazoles, substituted benzimidazoles, b r o m o f e n o x i m , s u b s t i t u t e d 2 , 6 - d i n i t r o a n i l i n e s , p y r i d i n o l s , and substituted 1,2,4-thiadiazoles (2). Electron Acceptors. Compounds c l a s s i f i e d as e l e c t r o n a c c e p t o r s c a n compete w i t h some component o f t h e e l e c t r o n t r a n s ­ p o r t pathway and s u b s e q u e n t l y be r e d u c e d . F e r r i c y a n i d e , PMS, and FMN, w h i c h a r e u s e d t o s t u d y p a r t i a l r e a c t i o n s o f t h e p h o t o c h e m i ­ c a l p a t h w a y , o p e r a t e i n t h i s manner. However, t h e y a r e n o t phytοtoxic. B i p y r i d y l i u m s w i t h r e d o x p o t e n t i a l s i n t h e r a n g e o f -300 to -500 mV, s u c h as d i q u a t and p a r a q u a t , can a c c e p t e l e c t r o n s i n c o m p e t i t i o n w i t h t h e a c c e p t o r o f p h o t o s y s t e m I ( F i g u r e 2, s i t e 4) and h a v e h e r b i c i d a l a c t i v i t y . I n t e r c e p t i o n of e l e c t r o n flow from photosystem I e s s e n t i a l l y shunts the e l e c t r o n t r a n s p o r t c h a i n . The b i p y r i d y l i u m s s u p p o r t b o t h n o n c y c l i c and c y c l i c p h o t o p h o s ­ p h o r y l a t i o n , a r e p h o t o r e d u c e d by i l l u m i n a t e d c h l o r o p l a s t s u n d e r a n a e r o b i c c o n d i t i o n s , and i n h i b i t t h e p h o t o r e d u e t i o n o f NADP. T h i s i n h i b i t i o n i s n o t c i r c u m v e n t e d by t h e a d d i t i o n o f r e d u c e d DPIP ( 1 0 ) . Structure-activity

Studies.

The H i l l r e a c t i o n has s e r v e d as a t a r g e t f o r s t r u c t u r e a c t i v i t y studies with phenylureas, tf-phenylcarbamates> polycyclic ureas, a c y l a n i l i d e s , s - t r i a z i n e s , u r a c i l s , dihalogenated benzoni-

4.

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Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch004

t r i l e s , a z i d o - s - t r i a z i n e s , 1 , 2 , 4 - t r i a z i n o n e s , i m i d a z o l e s , and b e n z i m i d a z o l e s (6^ 11) . The o b j e c t i v e s o f t h e s e s t u d i e s h a v e b e e n t o (a) i d e n t i f y t h e s u b s t i t u e n t s r e q u i r e d f o r maximum i n ­ h i b i t i o n , (b) r e l a t e the c h e m i c a l a n d p h y s i c a l p r o p e r t i e s o f t h e h e r b i c i d e s t o the i n h i b i t o r y a c t i o n , (c)determine the e n v i r o n ­ ment i n w h i c h t h e i n h i b i t o r s o p e r a t e , a n d (d) i d e n t i f y i n t e r ­ a c t i o n s between s u b s t i t u e n t s o f t h e i n h i b i t o r s and the p o s t u l a t e d receptors I n the c h l o r o p l a s t s . P h e n y l a m i d e I n h i b i t o r s . Some o f t h e e a r l i e s t s t r u c t u r e a c t i v i t y s t u d i e s , w h i c h i n v o l v e d t h e s u b s t i t u t e d a m i d e s , showed t h a t the s t r o n g e s t i n h i b i t o r s had a r i n g s y s t e m bonded t o t h e n i t r o g e n o f t h e amide m o i e t y a n d a f r e e a n d s t e r i c a l l y u n h i n d e r e d amide h y d r o g e n . D e r i v a t i v e s w i t h u n s a t u r a t e d r i n g s y s t e m s , r e p r e s e n t e d b y c h l o r o x u r o n a n d d i u r o n , w e r e more i n h i b i t o r y t h a n w e r e t h o s e w i t h s a t u r a t e d r i n g s y s t e m s , s u c h as n o r e a a n d c y cluron. I n h i b i t i o n was i n t e n s i f i e d when t h e r i n g was c h l o r i n a t e d i n a metaa n d the p a r a - r i n g p o s i t i o n s , a s i n d i u r o n a n d p r o p a n i L D e r i v a t i v e s m o n o c h l o r i n a t e d i n a metao r t h e para - r i n g p o s i t i o n , as i n c h l o r p r o p h a m a n d monuron, w e r e l e s s i n h i b i t o r y t h a n t h e 3 , 4 - d i c h l o r i n a t e d d e r i v a t i v e s , b u t w e r e more i n h i b i t o r y t h a n t h e u n s u b s t i t u t e d p a r e n t compounds. However, d e r i v a t i v e s c h l o r i n a t e d i n a n ortho p o s i t i o n were l e s s a c t i v e than the u n s u b s t i t u t e d p a r e n t compound. D i s u b s t i t u t e d i s o m e r s i n w h i c h a n ortho chlo­ r i n e was p a i r e d w i t h a meta o r a para c h l o r i n e were a l s o q u i t e i n a c t i v e (6) . I n h i b i t o r y a c t i o n was a s s o c i a t e d w i t h a w i d e v a r i e t y o f s t r u c t u r a l groups s u b s t i t u t e d o n the c a r b o n y l c a r b o n o f t h e amide m o i e t y . I n general, d e r i v a t i v e s with nonpolar s i d e chains w e r e more a c t i v e t h a n t h o s e w i t h p o l a r s i d e c h a i n s . The most a c t i v e i n h i b i t o r s , represented by d i u r o n , possessed a d i a l k y l amino s u b s t i t u e n t . However, d e r i v a t i v e s w i t h a l i p h a t i c s i d e c h a i n s , s u c h as p r o p a n i l , a n d a l i c y c l i c s i d e c h a i n s , s u c h as cypromid, were a l s o s t r o n g i n h i b i t o r s ( 6 ) . The r e q u i r e m e n t f o r a f r e e a n d s t e r i c a l l y u n h i n d e r e d a m i d e h y d r o g e n l e d t o t h e p o s t u l a t i o n t h a t t h e amide m o i e t y i n t e r a c t e d w i t h the r e c e p t o r i n the c h l o r o p l a s t s . Because o f the r e v e r s i ­ b i l i t y o f t h e i n h i b i t i o n , t h e i n t e r a c t i o n was c o n s i d e r e d t o i n ­ v o l v e weak b o n d s , c o n c e i v a b l y h y d r o g e n b o n d s . S u b s t i t u e n t P a r a m e t e r s . A s i g n i f i c a n t a d v a n c e was made, i n t h e s t r u c t u r e - a c t i v i t y s t u d i e s w i t h t h e H i l l r e a c t i o n , when H a n s e n a n d D e u t s c h (12) e v a l u a t e d some o f t h e p u b l i s h e d H i l l i n ­ h i b i t i o n data with a m u l t i p l e regression a n a l y s i s , an e x t r a t h e r m o d y n a m i c a p p r o a c h , o r t h e s o - c a l l e d s i g m a , p i (σ, Ή) r e ­ g r e s s i o n a n a l y s i s . The p r i n c i p l e o f t h e a p p r o a c h r e s t s on t h e a s s u m p t i o n t h a t changes i n b i o l o g i c a l a c t i v i t y c a n be c o r r e ­ l a t e d w i t h measurable molecular o r s u b s t i t u e n t parameters. This a n a l y s i s i n v o l v e d equations o f the f o l l o w i n g type:

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Figure 3. Correlation of pl and partition data for some substituted phenyldimethylureas and isopropyl N-phenylcarbamates [adapted from Hansch and Deutsch (12)] 50

4.

MORELAND

Action

of

PI50

65

Herbicides

= βπ + bcrt-cE

s

+ d

where π i s a p a r t i t i o n c o e f f i c i e n t o b t a i n e d i n a n o c t a n o l / w a t e r s y s t e m , σ i s t h e Hammett s u b s t i t u e n t p a r a m e t e r , E i s t h e T a f t s t e r i c f a c t o r , and a , b, c, and d a r e c o n s t a n t s . The p a r t i t i o n c o e f f i c i e n t was o b t a i n e d f r o m t h e f o l l o w i n g e q u a t i o n : s

ττχ = l o g

P

X

- log

P

H

where P J J i s t h e p a r t i t i o n c o e f f i c i e n t o f t h e u n s u b s t i t u t e d parent molecule and Ρ i s the p a r t i t i o n c o e f f i c i e n t o f the de­ rivative. H e n c e , π becomes t h e l o g a r i t h m o f t h e p a r t i t i o n c o ­ e f f i c i e n t o f t h e s u b s t i t u e n t X. Examples o f c o r r e l a t i o n s p u b l i s h e d by Hansch and Deutsch (12) a r e shown i n F i g u r e 3. The r e l a t i o n b e t w e e n π a n d o b s e r v e d P I 5 0 values f o r a s e r i e s o f meta-substituted i s o p r o p y l ^-phenylcarbamates i s presented i n t h e lower curve. The u p p e r c u r v e shows a s i m i l a r r e l a t i o n f o r a s e r i e s o f metaand p a r a - s u b s t i ­ tuted phenylureas. I n both examples, r e g r e s s i o n analyses sug­ g e s t e d t h a t a p p r o x i m a t e l y 92% o f t h e o b s e r v e d r e s p o n s e s c o u l d be a t t r i b u t e d to the l i p o p h i l i c i t y , o r the hydrophobic bonding power, o f the r i n g s u b s t i t u e n t s . The a d d i t i o n o f Hammett s u b ­ s t i t u e n t and T a f t s t e r i c c o n s t a n t s t o t h e e q u a t i o n s d i d n o t i m ­ prove s i g n i f i c a n t l y the r e g r e s s i o n c o e f f i c i e n t s . Hence, e l e c ­ t r o n i c c o n t r i b u t i o n s were c o n s i d e r e d t o be o f minor importance i n the expression o f i n h i b i t i o n . Based p a r t l y on t h e above r e s u l t s , Hansch (13) s u b s e q u e n t l y postulated that f o r the a c y l a n i l i d e s , u r a c i l s , benzimidazoles, i m i d a z o l e s , and t r i a z i n e s , the s i t e o f a c t i o n i n the c h l o r o p l a s t s i n v o l v e d the amide l i n k a g e o f s t r a t e g i c a l l y l o c a t e d p r o t e i n s ( F i g u r e 4 ) . A good i n h i b i t o r h a d a l a r g e l i p o p h i l i c m o i e t y t h a t bound to the h y d r o p h o b i c a r e a and a p o l a r f u n c t i o n t h a t anchored the i n h i b i t o r t o t h e r e c e p t o r . The s y s t e m h a d a p l a n a r a r r a n g e ­ ment. I n h i b i t o r s w e r e a l s o c h a r a c t e r i z e d b y h a v i n g a n N-H g r o u p a t t a c h e d t o a n e l e c t r o n - d e f i c i e n t s p c a r b o n atom. Binding o f t h e i n h i b i t o r was v i s u a l i z e d as o c c u r r i n g b e t w e e n t h e l o n e p a i r e l e c t r o n s o f t h e h e r b i c i d e n i t r o g e n and t h e e l e c t r o n - d e f i c i e n t c a r b o n y l o f t h e p r o t e i n amide g r o u p . B i n d i n g was p o s t u l a ­ t e d t o i n v o l v e s o m e t h i n g b e t w e e n a c o m p l e t e c h a r g e - t r a n s f e r com­ p l e x and a simple d i p o l e i n t e r a c t i o n , p o s s i b l y r e i n f o r c e d by h y d r o g e n bonds ( 1 3 ) .

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch004

χ

2

H e t e r o c y c l i c I n h i b i t o r s . Around 1968, r e s u l t s o b t a i n e d w i t h a new g e n e r a t i o n o f H i l l i n h i b i t o r s , w h i c h l a c k e d a f r e e amide h y d r o g e n , began t o appear i n t h e l i t e r a t u r e . A v e r y com­ p l e t e s t r u c t u r e - a c t i v i t y s t u d y was c o n d u c t e d b y D r a b e r et al. ( 1 4 , 15) w i t h numerous 1 , 2 , 4 - t r i a z i n o n e s . C o r r e l a t i o n s w e r e made w i t h the m u l t i p l e r e g r e s s i o n approach i n t r o d u c e d by Hansch. From t h i s s t u d y , D r a b e r et al. c o n c l u d e d ( F i g u r e 5) t h a t was i n ­ v o l v e d i n the b i n d i n g t o t h e r e c e p t o r , p o s s i b l y by c r e a t i n g a

Figure 4.

I

Y

C=0

T-

R Triazines

H-N

H-N

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Uracils

H-N

Imidazoles

H-N

Anilides Carbamates Ureas

Benzimi dazoles

H-N

I

Protein

H-N

Interaction of structural elements of herbicidal inhibitors of photosystem II with a postulated receptor protein [adapted from Hansch (13)]

Protein

H-N

C=0

Hydrophobic Area

H-N

c=o

-ν

Hydrophobic Area

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch004

Ο

M

H

S

M

a

M H Q

MORELAND

Action

of

Herbicides

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch004

Ο

Rl

= Hj N H ,

R2 = SR, R3

OR,

2

OR,

= ALKYL,

NRR',

NRR', ARYL,

ALKYL:

ALKYL:

BINDS

STERIC

HETEROARYL:

TO RECEPTOR

CONTRIBUTION

CONTRIBUTES LIPOPHILICITY

(CH ) 3

METRIBUZIN (

P

I

5

0

= 6.6)

BAY ( p l

138,992 5

0

=

8.0)

Figure 5. 1,2,4-Triazinones tested and contributions made by molecular substituents in the inhibition of photosystem II [adapted from Draber et al. (15)]

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68

PESTICIDE C H E M I S T R Y IN T H E 2 0 T H C E N T U R Y

favorable e l e c t r o n d i s t r i b u t i o n on theh e t e r o c y c l i c r i n g . R 2 c o n t r i b u t e d o r p o s s e s s e d a s t e r i c p r o p e r t y t h a t was e s p e c i a l l y c r i t i c a l f o r a good f i t a t t h e r e c e p t o r . R 3 contributed l i p o p h i l i c i t y t o t h e whole m o l e c u l e and thus i n f l u e n c e d p e n e t r a b i l i t y and u n s p e c i f i c b i n d i n g . These p r o p e r t i e s were m a x i m i z e d i n m e t r i b u z i n and i n compound BAY 138,992. The l a t t e r compound, w i t h a P I 5 0 v a l u e o f 8.0 i s one o f t h e s t r o n g e s t i n h i b i t o r s o f the H i l l r e a c t i o n t h a t h a s b e e n r e p o r t e d . D r a b e r et al. a g r e e d w i t h Hansen's s u g g e s t i o n t h a t t h e f r e e e l e c t r o n p a i r o f t h e h e t e r o c y c l i c n i t r o g e n a d j a c e n t t o t h e c a r b o n y l f u n c t i o n bound t o the r e c e p t o r . They f a v o r e d e l i m i n a t i o n o f t h e h y d r o g e n b o n d i n g p o s t u l a t e and s t r e s s e d involvement o f a hydrophobic interchange or charge-transfer i n t e r a c t i o n . The s t r u c t u r e s o f some a d d i t i o n a l h e t e r o c y c l i c H i l l i n h i b i ­ t o r s t h a t l a c k a f r e e amide h y d r o g e n a r e shown i n F i g u r e 6. B e n z t h i a z o l e - a n d t h i a d i a z o l o n e - u r e a s h a v e t h e amide h y d r o g e n r e ­ p l a c e d w i t h a methyl group. Other f a m i l i e s t h a t c o n t a i n h e t e r o ­ c y c l i c amides a r e shown i n w h i c h t h e f r e e h y d r o g e n s h a v e b e e n r e p l a c e d w i t h b e n z e n e r i n g s . I n c l u d e d a r e p y r r o l i d o n e (Rohm & Haas's BV-207), p y r i d a z i n o n e s ( p y r a z o n and n o r f l u r a z o n ) , p y r a ­ z o l o n e s , t r i a z o l o n e s (BAY 1 4 3 , 8 7 3 ) , a n d o x a d i a z o l i n o n e (Rhodia's o x a d i a z o n ) (16) . T r e b s t a n d H a r t h ( 1 6 ) i n r e v i e w i n g t h e s e s t r u c t u r e s n o t e d t h a t t h e common e l e m e n t i n t h e h e t e r o c y c l i c r i n g ν a was t h e -N-C- m o i e t y . They a g r e e d w i t h D r a b e r et al. t h a t b i n d i n g probably involved the free e l e c t r o n p a i r o f the h e t e r o c y c l i c n i t r o g e n a n d was consummated b y a h y d r o p h o b i c i n t e r c h a n g e o r a charge-transfer i n t e r a c t i o n . Some good i n h i b i t o r s o f t h e H i l l r e a c t i o n , h o w e v e r , do n o t c o n t a i n t h e c a r b o n y l o x y g e n - n i t r o g e n moiety. Examples a r e t h e d i n i t r o a n i l i n e s , diphenylethers, 2,4-dinitrophenols, halogenated b e n z o n i t r i l e s , and p y r i d i n o l s . Hence, t h e p o s t u l a t e s proposed are n o t a l l i n c l u s i v e . Three o f these h e r b i c i d e s a r e phenols. Under p h y s i o l o g i c a l p H s , t h e m o l e c u l e s c a n be e x p e c t e d t o be i o n i z e d , a n d i t may be t h e i o n i z e d f o r m o f t h e m o l e c u l e t h a t binds to the receptor. f

Steric Relations. Some i n t e r e s t i n g s p e c i f i c i t y h a s b e e n documented t h a t r e f l e c t s a r e q u i r e m e n t f o r a d e f i n i t e s t e r i c approach o f an i n h i b i t o r t o t h e r e c e p t o r i n t h e c h l o r o p l a s t s . One e x a m p l e i s p r o v i d e d b y t h e o p t i c a l i s o m e r s o f l - ( a - m e t h y l benzyl)-3-(3,4-dichlorophenyl)urea (17) . T h i s c h e m i c a l i s an i n h i b i t o r y u n c o u p 1 e r . The S - i s o m e r i n h i b i t s e l e c t r o n t r a n s p o r t , b u t t h e R - i s o m e r i s n o n i n h i b i t o r y . The i n a c t i v e i s o m e r does n o t compete w i t h t h e a c t i v e i s o m e r a t t h e p h o t o s y s t e m I I s i t e . The p h o s p h o r y l a t i o n s i t e shows no o p t i c a l s p e c i f i c i t y . The two i s o m e r s do n o t d i f f e r s i g n i f i c a n t l y i n t h e i r l i p o p h i l i c i t y . Hence, t h e d i f f e r e n c e i n i n h i b i t o r y a c t i v i t y i s n o t r e l a t e d t o p a r t i t i o n i n g behavior.

Figure 6.

N-CH

3

Ν

Triazolone 4.70

Η

Ι

CH

Π

3

Ν '

7

Ο

Ν 3

C(CH )

Oxadiazol inone 4.54

Cl

3

0-C H

3

-

Ν Ι /,,k

ς

C

ι

H

_

^ 3

3

Numbers

\

Ν ο M II /CH >N-C-N

Thiadiazolone - urea 7.27

α

Structural elements of some heterocyclic inhibitors of photosystem Π [adapted from Trebst and Harth (16)]. below the chemical names are pho values.

Pyrazolone 4.25

Ν

Cl

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70

PESTICIDE C H E M I S T R Y IN

THE

20TH C E N T U R Y

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch004

An e x a m p l e o f g e o m e t r i c i s o m e r i s m i s p r o v i d e d by t h e dimethylpyrrolidinecarboxanilides (18). O n l y when t h e m e t h y l g r o u p s s u b s t i t u t e d on t h e p y r r o l i d i n e r i n g a r e i n t h e cisc o n f o r m a t i o n i s e l e c t r o n t r a n s p o r t i n h i b i t e d and p h y t o t o x i c i t y p r o d u c e d . The trans-isomer n e i t h e r i n h i b i t s the H i l l r e a c t i o n , nor i s i t p h y t o t o x i c . Status of S t r u c t u r e - a c t i v i t y Studies. Many d i v e r s e l y s t r u c ­ t u r e d c h e m i c a l s a r e known t o i n h i b i t t h e p h o t o i n d u c e d c h l o r o p l a s t reactions. Each y e a r , a d d i t i o n a l types o f chemistry are added to t h e l e n g t h y l i s t o f i n h i b i t o r y s t r u c t u r e s . H o w e v e r , t o d a t e , no p o s t u l a t e has b e e n p r e s e n t e d t h a t s a t i s f a c t o r i l y e x p l a i n s w h e r e and how i n h i b i t i o n i s p r o d u c e d . P a r t o f o u r i n a b i l i t y t o f i t t h e many s t r u c t u r e - a c t i v i t y o b s e r v a t i o n s i n t o a g i v e n model r e l a t e s t o o u r u n c e r t a i n t y as t o w h e t h e r a l l o f the i n h i b i t o r s f u n c t i o n a t p r e c i s e l y t h e same s i t e t h r o u g h a common mechanism o r w h e t h e r t h e d i f f e r e n t i n h i b i t o r s a f f e c t d i f f e r e n t , but possibly c l o s e l y s i t u a t e d , s i t e s . I n view o f t h e e x t r e m e s t r u c t u r a l d i s s i m i l a r i t i e s among t h e v a r i o u s i n ­ h i b i t o r s , one c o u l d c o n c l u d e t h a t i t i s u n l i k e l y t h a t a l l r e a c t a t t h e same s i t e . However, we h a v e l i t t l e e v i d e n c e t h a t t h e y do n o t do s o . The r e g r e s s i o n a n a l y s e s h a v e shown t h a t i n h i b i t o r y p o t e n c y e x p r e s s e d a g a i n s t t h e H i l l r e a c t i o n c a n be c o r r e l a t e d w i t h p h y s i ­ c o - c h e m i c a l p a r a m e t e r s w i t h i n a p a r t i c u l a r group o f h e r b i c i d e s . However, no i n v e s t i g a t o r has s u c c e s s f u l l y c o r r e l a t e d m a t h e m a t i ­ cally a c t i v i t i e s between d i f f e r e n t c h e m i c a l f a m i l i e s ( 1 1 ) . A l s o , no e v i d e n c e e x i s t s f o r t h e " s p e c i a l " p r o t e i n amide p o s t u ­ l a t e d by H a n s c h (13) . E v e n t h o u g h t h e m o d e l s a r e o n l y c r u d e a p p r o x i m a t i o n s , they p r o v i d e a b a s i s f o r the development o f h y p o t h e s e s t h a t c a n be c r i t i c a l l y i n v e s t i g a t e d . I n a d d i t i o n , an i n s i g i h t i s b e i n g g a i n e d i n t o how h e r b i c i d e s and r e c e p t o r s m i g h t interact. Studies

with

Intact Plants.

I n s o f a r as t h e y h a v e b e e n s t u d i e d , a l l h e r b i c i d e s t h a t i n ­ h i b i t the H i l l r e a c t i o n o f i s o l a t e d c h l o r o p l a s t s a l s o i n h i b i t photosynthesis o f i n t a c t p l a n t s and p h o t o s y n t h e t i c m i c r o o r g a n i s m s (_2, 3) . P h y t o t o x i c i t y i s p r o d u c e d o n l y i n t h e l i g h t , and s e v e r i t y o f symptoms i s p r o p o r t i o n a l t o l i g h t i n t e n s i t y . Studies with l i g h t q u a l i t y h a v e i n d i c a t e d t h a t the c h l o r o p h y l l s a r e t h e p r i n ­ c i p a l a b s o r b i n g pigments i n v o l v e d i n the p r o d u c t i o n o f phyto­ toxicity. The d e v e l o p m e n t o f t o x i c symptoms on p l a n t s t r e a t e d w i t h p u r e e l e c t r o n t r a n s p o r t i n h i b i t o r s , s u c h as s i m a z i n e , d i u r o n , and t h e u r a c i l s , c a n be p r e v e n t e d i f the p l a n t s a r e s u p p l i e d e x o ­ genous l y w i t h a r e s p i r a b l e c a r b o h y d r a t e ( 2 ) . T h i s observation s u g g e s t s t h a t t h e g l y c o l y t i c o r t h e m i t o c h o n d r i a l s y s t e m can p r o v i d e s u f f i c i e n t energy t o p r e v e n t the appearance o f p h y t o -

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch004

4.

MOREL AND

Action

of

Herbicides

71

t o x i c symptoms, i f r e s p i r a b l e s u b s t r a t e s a r e p r o v i d e d . I n con­ t r a s t , c a r b o h y d r a t e p r o t e c t i o n c o u l d n o t be d e m o n s t r a t e d w i t h i n h i b i t o r y u n c o u p l e r s o r w i t h u n c o u p l e r s , s u c h as c h l o r p r o p h a m , i o x y n i l , and d i n o s e b , t h a t i n t e r f e r e a l s o w i t h o x i d a t i v e p h o s ­ phorylation. A number o f h e r b i c i d e s t h a t i n t e r f e r e w i t h t h e p h o t o c h e m i s ­ t r y of c h l o r o p l a s t s have been r e p o r t e d a l s o to a l t e r the u l t r a s t r u c t u r e o f c h l o r o p l a s t s . These i n c l u d e b r o m a c i l , haloxydine, p y r a z o n , 2,4-D, monuron, d i u r o n , S a n d o z 6 7 0 6 , and t h e b i p y r i dyliums (2, 19). The f i r s t e f f e c t o b s e r v e d i s a s w e l l i n g o f t h e i n t e r g r a n a l t h y l a k o i d s , sometimes w i t h i n 2 h o u r s a f t e r the h e r b i ­ c i d e i s a p p l i e d t o the r o o t s . Subsequently, the t h y l a k o i d s s w e l l , b e g i n n i n g w i t h the o u t e r t h y l a k o i d s , u n t i l the w h o l e l a m e l l a r s y s t e m becomes d i s o r g a n i z e d . L a t e r , t h e t o n o p l a s t and c h l o r o p l a s t e n v e l o p e s r u p t u r e , and f i n a l l y t h e t h y l a k o i d membranes rupture. M i x i n g o f p l a s t i d and c y t o p l a s m i c c o n t e n t s has b e e n o b s e r v e d w i t h i n 4 h o u r s a f t e r t r e a t m e n t . E x t e r n a l symptoms o f i n j u r y a r e u s u a l l y n o t a p p a r e n t u n t i l 3 o r 4 days a f t e r t r e a t ­ ment w i t h e l e c t r o n t r a n s p o r t i n h i b i t o r s . Hence, the i n t e r n a l m o r p h o l o g y i n l e a v e s i s d e s t r o y e d ( w i t h i n a few h o u r s ) l o n g b e f o r e e x t e r n a l symptoms a p p e a r . I n e v e r y s t u d y , l i g h t was r e q u i r e d f o r t h e e f f e c t s o f t h e i n h i b i t o r s t o become a p p a r e n t . Chloroplasts of h e r b i c i d e t r e a t e d p l a n t s k e p t i n the dark resembled, i n a l l r e s p e c t s , c h l o r o p l a s t s of the d a r k - c o n t r o l p l a n t s . The m o d i f i c a t i o n s p r o ­ duced i n c h l o r o p l a s t s a r e not unique to h e r b i c i d e s . M i n e r a l and v i t a m i n d e f i c i e n c i e s , a n t i b i o t i c s , u n n a t u r a l p y r i m i d i n e s , and genetic a l t e r a t i o n s a l l cause s i m i l a r aberrant u l t r a s t r u c t u r a l changes i n c h l o r o p l a s t s ; however, the e x t e n t of the d i s r u p t i o n s p r o d u c e d by h e r b i c i d e s i s more e x t r e m e . The c h a n g e s i n d u c e d by h e r b i c i d e s a r e s i m i l a r i n many r e s p e c t s t o t h o s e t h a t o c c u r i n normal senescence, r e f l e c t i n g the c h a r a c t e r i s t i c p a t t e r n a s s o ­ c i a t e d w i t h d e g e n e r a t i o n and d e a t h o f a c e l l . S u c r o s e h a s b e e n shown t o r e v e r s e t h e e f f e c t o f a t l e a s t monuron a l t e r a t i o n s t o t h e f i n e s t r u c t u r e o f c h l o r o p l a s t s . A l l of the i n j u r y , i n c l u d i n g t h a t d e t e c t a b l e a t the u l t r a s t r u c t u r a l l e v e l , a p p a r e n t l y c a n be p r e v e n t e d i f t h e e n e r g y s u p p l y c a n be k e p t f u l l y c h a r g e d t h r o u g h t h e g l y c o l y t i c and m i t o c h o n d r i a l s y s t e m s , by the f e e d i n g of r e s p i r a b l e s u b s t r a t e s . However, carbohydrates w i l l not p r o t e c t a g a i n s t the h e r b i c i d e s t h a t i n t e r f e r e w i t h o x i d a t i v e p h o s p h o r y l a t i o n ( u n c o u p l e r s and i n h i K * ) tory uncouplers). Postulated

Modes o f

Action.

The r e l a t i o n b e t w e e n i n h i b i t i o n o f t h e p h o t o i n d u c e d r e s p o n s e s i n i s o l a t e d c h l o r o p l a s t s and t h e e x p r e s s i o n o f p h y t o t o x i c i t y r e m a i n s t o be i d e n t i f i e d p o s i t i v e l y . Any hypothesis p r o p o s e d t o a c c o u n t f o r t h e mode o f a c t i o n must t a k e i n t o c o n ­ sideration that: (a) p h y t o t o x i c symptoms d e v e l o p o n l y i n t h e l i g h t , and s e v e r i t y i s p r o p o r t i o n a l t o l i g h t i n t e n s i t y ; (b)

72

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20TH

CENTURY

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch004

c a r b o n d i o x i d e f i x a t i o n i s i n h i b i t e d o n l y i n t h e l i g h t ; (c) t o x i c e f f e c t s c a n be a l l e v i a t e d by t h e exogenous a p p l i c a t i o n o f r e s p i r a b l e c a r b o h y d r a t e s ; (d) s e v e r e m o r p h o l o g i c a l and c y t o l o g i c a l changes a r e i n d u c e d o n l y i n t h e l i g h t ; and (e) e x t e r n a l symptoms become a p p a r e n t i n h i g h e r p l a n t s s e v e r a l days a f t e r t r e a t m e n t , e x c e p t f o r t h e b i p y r i d y l i u m s (2). S e v e r a l hypotheses have been proposed to account f o r the p h y t o t o x i c i t y o f the H i l l i n h i b i t o r s , b u t none has b e e n s u b s t a n t i a t e d b y r i g o r o u s e x p e r i ­ mentation. Starvation. The e a r l y r e p o r t s t h a t H i l l i n h i b i t o r s l i m i t e d p h o t o s y n t h e s i s and t h a t s t a r c h d i s a p p e a r e d * f r o m t r e a t e d p l a n t s , p r o m p t e d some i n v e s t i g a t o r s t o r e f e r t o t h e s e compounds as photosynthesis i n h i b i t o r s . Photosynthesis i s i n h i b i t e d because ATP and NADPH a r e n o t a v a i l a b l e f o r c a r b o n d i o x i d e f i x a t i o n . However, t h e r e i s l i t t l e e v i d e n c e t h a t t h e p l a n t s s t a r v e t o d e a t h . I f t h i s w e r e t h e o n l y p r o c e s s a f f e c t e d , p h y t o t o x i c symp­ toms s h o u l d r e s e m b l e t h o s e t h a t a p p e a r on p l a n t s k e p t i n t o t a l d a r k n e s s . D e f i c i e n c y o f p h o t o s y n t h a t e does l i m i t new g r o w t h , b u t does n o t a c c o u n t f o r t h e m o r p h o l o g i c a l a l t e r a t i o n s t h a t o c c u r w i t h i n a few h o u r s a f t e r t r e a t m e n t . The mechanisms t h a t l e a d t o p h y t o t o x i c i t y a p p e a r t o be c o n s i d e r a b l y more c o m p l e x t h a n w o u l d r e s u l t f r o m l i m i t i n g c a r b o h y d r a t e s y n t h e s i s by s u p p r e s s i o n o f c a r b o n d i o x i d e f i x a t i o n (2) . F r e e R a d i c a l M e c h a n i s m s . The a p p e a r a n c e o f p h y t o t o x i c symptoms o n l y i n t h e l i g h t a f t e r t r e a t m e n t o f p l a n t s w i t h h e r b i ­ c i d e s s u c h as d i u r o n and a t r a z i n e p r o m p t e d some i n v e s t i g a t o r s t o propose " l i g h t - a c t i v a t i o n " h y p o t h e s e s , the f o r m a t i o n of t o x i c s u b s t a n c e s , or the f o r m a t i o n o f r e a c t i v e f r e e r a d i c a l s . However, e x c e p t f o r t h e s t r o n g d o c u m e n t a t i o n on t h e f o r m a t i o n o f f r e e r a d i c a l s by b i p y r i d i l i u m s , t h e r e i s no d i r e c t e v i d e n c e t h a t t o x i c components a r e f o r m e d f r o m an i n t e r a c t i o n b e t w e e n a h e r b i c i d a l H i l l i n h i b i t o r and l i g h t (2) . Pigment S y n t h e s i s . A m i t r o l e , fluometuron, dichlormate, m e t f l u r a z o n e , Sandoz 9774, h a l o x y d i n e , and p y r i c l o r i n h i b i t o r i n t e r f e r e w i t h c a r o t e n o i d b i o s y n t h e s i s (2). Carotenoid pigments i n p h o t o s y n t h e t i c s y s t e m s may p r o t e c t a g a i n s t p h o t o s e n s i t i z e d o x i d a t i o n s , w h i c h o c c u r when l i g h t - e x c i t e d c h l o r o p h y l l s combine w i t h m o l e c u l a r oxygen. A m i t r o l e i s the o n l y h e r b i c i d e , of t h i s g r o u p , t h a t does n o t a f f e c t t h e H i l l r e a c t i o n . M o s t o f t h e H i l l i n h i b i t o r s do n o t a f f e c t c a r o t e n o i d s y n t h e s i s . I n t e r f e r e n c e w i t h e i t h e r the H i l l r e a c t i o n or pigment s y n t h e s i s c o u l d cause p l a n t death. E n e r g y (ATP) A v a i l a b i l i t y . A l l of the h e r b i c i d e s t h a t i n t e r f e r e w i t h the photoinduced r e a c t i o n s l i m i t the a v a i l a b i l i t y o f ATP. A c t i o n i s e x p r e s s e d a t d i f f e r e n t s i t e s on t h e e l e c t r o n t r a n s p o r t and e n e r g y g e n e r a t i o n p a t h w a y s , b u t t h e n e t r e s u l t i s

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch004

4.

MOREL AND

Action

of

Herbicide s

73

t h e same. I n t e r f e r e n c e w i t h ATP p r o d u c t i o n h a s f o c u s e d a t t e n t i o n on how t h i s a c t i o n m i g h t r e l a t e t o t h e p r o d u c t i o n o f p h y t o t o x i ­ city. ATP has a u b i q u i t o u s and d o m i n a n t r o l e i n c e l l u l a r metabo­ lism. T h i s r o l e c a n be a p p r e c i a t e d more f u l l y i f c o g n i z a n c e i s extended to the energy requirements of c e l l s , to the r e g u l a t i o n o f c e l l u l a r a c t i v i t y and m e t a b o l i s m i m p o s e d by ATP, and t o what i n t e r f e r e n c e w i t h ATP p r o d u c t i o n means to t h e g r o w t h o f a c h l o r o phyllous plant. P l a n t s s t o r e o x i d a t i v e and p h o t o c h e m i c a l e n e r g y i n t h e t e r m i n a l p h o s p h a t e b o n d s o f ATP. The t e r m i n a l b o n d e n e r g y i s u s e d s u b s e q u e n t l y t o p e r f o r m t h e c h e m i c a l , m e c h a n i c a l , and osmotic work of the c e l l . O n l y ADP i s p h o s p h o r y l a t e d to f o r m ATP i n g l y c o l y s i s , o x i ­ d a t i v e p h o s p h o r y l a t i o n , and p h o t o p h o s p h o r y l a t i o n . ATP provides t h e e n e r g y , d i r e c t l y o r i n d i r e c t l y , t o d r i v e most b i o s y n t h e t i c reactions. The f u n c t i o n s o f membranes s u c h as a c t i v e t r a n s p o r t and o s m o t i c r e l a t i o n s , w h i c h r e g u l a t e t h e v o l u m e o f c e l l s , a r e e n e r g y d e p e n d e n t . The s t r u c t u r a l o r g a n i z a t i o n , c o n t r a c t i o n , and o r i e n t a t i o n o f chromosomes and m i c r o t u b u l e s o f the s p i n d l e a p p a r ­ a t u s d u r i n g m i t o s i s depend on ATP e n e r g y . The i n t r a c e l l u l a r c o n c e n t r a t i o n s and s t o i c h i o m e t r i c r e l a t i o n s o f ATP, ADP, and AMP a l s o modulate c e l l u l a r metabolism. The o b s e r v a t i o n s t h a t p h y t o t o x i c symptoms d e v e l o p o n l y i n the l i g h t s u g g e s t t h a t the demand f o r ATP i s i n c r e a s e d when c h l o r o p h y l l o u s organisms are i l l u m i n a t e d . A c t u a l l y , a l a r g e number o f e n e r g y - r e q u i r i n g b i o s y n t h e t i c r e a c t i o n s a r e now known t o be l i g h t - a c t i v a t e d . These i n c l u d e ΕΝΑ and p r o t e i n s y n t h e s i s ; v a r i o u s enzymes i n v o l v e d i n t h e s y n t h e s i s o f c h l o r o p h y l l , o t h e r p i g m e n t s , and l i p i d s ; and many o f t h e enzymes o f t h e c a r b o n d i o x i d e f i x a t i o n pathways. T u r n o v e r o f o t h e r c e l l u l a r components i s a l s o a c t i v a t e d by l i g h t . A l l o f the l i g h t - a c t i v a t e d s y n t h e t i c a c t i v i t y p l a c e s a much h i g h e r demand upon t h e p l a n t f o r e n e r g y i n the l i g h t than i n the d a r k . I n e v a l u a t i n g the r o l e o f ATP i n t h e c e l l u l a r m e t a b o l i s m o f h i g h e r p l a n t s , a l l p r o c e s s e s t h a t c o n t r i b u t e t o t h e ATP pool ( g l y c o l y s i s , o x i d a t i v e p h o s p h o r y l a t i o n , and p h o t o p h o s p h o r y l a t i o n ) must be c o n s i d e r e d . Even though the p h o t o s y s t e m I I i n h i b i t o r s block noncyclic photophosphorylation, ATP c a n s t i l l be p r o d u c e d in vivo u n d e r some c o n d i t i o n s by c y c l i c p h o t o p h o s p h o r y l a t i o n , by g l y c o l y s i s , and t h r o u g h o x i d a t i v e p h o s p h o r y l a t i o n . Apparently, s u f f i c i e n t e n e r g y c a n be p r o v i d e d t h r o u g h t h e l a s t two p r o c e s s e s , i f r e s p i r a b l e carbohydrates are s u p p l i e d exogenously, to s a t i s f y t h e l i g h t - i n d u c e d demands and p r e v e n t p h y t o t o x i c symptoms. The u n c o u p l e r s and i n h i b i t o r y u n c o u p l e r s i n t e r f e r e w i t h t h e m i t o ­ c h o n d r i a l p r o d u c t i o n o f ATP, and c a r b o h y d r a t e s do n o t p r o t e c t against their action (2). Many, i f n o t a l l , o f t h e b i o c h e m i c a l , p h y s i o l o g i c a l , and m o r p h o l o g i c a l a l t e r a t i o n s o b s e r v e d f o l l o w i n g a p p l i c a t i o n o f the H i l l i n h i b i t o r s t o p l a n t s c a n be a c c o u n t e d f o r on t h e b a s i s o f i n t e r f e r e n c e w i t h ATP p r o d u c t i o n . W i t h o u t the n e e d e d ATP, growth s t o p s , c e l l u l a r f u n c t i o n s are a r r e s t e d , the i n t e g r i t y of the

74

PESTICIDE C H E M I S T R Y IN T H E 20TH C E N T U R Y

f

cell s

s t r u c t u r a l morphology i s l o s t ,

and the p l a n t

dies.

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch004

Conclusions. F u t u r e r e s e a r c h may show t h a t none o f t h e h y p o t h e s e s d i s ­ cussed accounts f o r the a c t i o n o f h e r b i c i d e s t h a t i n t e r f e r e w i t h t h e p h o t o c h e m i s t r y o f i s o l a t e d c h l o r o p l a s t s . No s i n g l e h y p o t h e ­ s i s may e x p l a i n a d e q u a t e l y t h e a c t i o n o f a l l i n h i b i t o r y h e r b i ­ c i d e s u n d e r a l l c o n d i t i o n s . W i t h a g i v e n h e r b i c i d e , a t one c o n ­ c e n t r a t i o n , when a p p l i e d t o a c e r t a i n s p e c i e s o r v a r i e t y o f p l a n t , a n d u n d e r p a r t i c u l a r e n v i r o n m e n t a l c o n d i t i o n s , one h y p o ­ t h e s i s may a c c o u n t f o r t h e o b s e r v e d p h y t o t o x i c i t y . H o w e v e r , u n d e r o t h e r c o n d i t i o n s o r s i t u a t i o n s , a n o t h e r h y p o t h e s i s may b e more a p p l i c a b l e (2) . B a s e d o n c u r r e n t k n o w l e d g e , i t seems l i k e l y t h a t w h a t e v e r f o r m t h e f i n a l h y p o t h e s i s may t a k e , i t w i l l c e n t e r a r o u n d w h a t h a p p e n s when t h e f o r m a t i o n o f ATP o r NADPH, o r b o t h , i s i n h i b i t e d a f t e r i n t e r f e r e n c e w i t h the photochemical r e a c t i o n s o f the c h l o ­ roplasts. H o p e f u l l y , t h e p o s t u l a t e s w i l l s e r v e as models t h a t can be s u b j e c t e d t o r i g o r o u s and s o p h i s t i c a t e d e x p e r i m e n t a t i o n , and w i l l b e m o d i f i e d a s o u r k n o w l e d g e o f b i o c h e m i c a l c o n t r o l systems i n h i g h e r p l a n t s i n c r e a s e s .

Literature

Cited.

1.

Corbett, J. R. "The Biochemical Mode of Action of P e s t i ­ cides", 330 p. Academic Press, London, 1974.

2.

Moreland, D. E., H i l t o n , J. L . In "Physiology and B i o ­ chemistry of Herbicides", pp. 493-523, L . J. Audus (ed.), Academic Press, London, 1976. (In press).

3.

Moreland, D. E. Annu. Rev. Plant P h y s i o l . 18:365-386.

4.

Ashton, F. M., Crafts, A. S. "Mode of Action of Herbicides", 504 p. John Wiley & Sons, New York, 1973.

5.

Jaworski, E. G. J. A g r i . Food Chem.

6.

Moreland, D. E. In "Progress i n Photosynthesis Research", V o l . III, pp. 1693-1711, H . Metzner (ed.), Tübingen, 1969.

7.

Duysens, L . Ν. Μ., Amesz, 64:243-260.

8.

Renger, R. Biochim. Biophys. Acta (1973)

9.

Hauska, G., Trebst, Α., K ö t t e r , C., Schulz, H. Z. Naturforsch. (1975) 30c:505-510.

J.

(1967)

(1972)

20:1195-1198.

Biochim. Biophys. Acta (1962) 314:113-116.

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4. MORELAND

Action of Herbicides

75

10.

Zweig, G., Shavit, Ν., Avron, M. Biochim. Biophys. Acta (1965) 109:332-346.

11.

Büchel, H. P e s t i c .

12.

Hansch, C., Deutsch, E. W. Biochim. Biophys. Acta (1966) 112:381-391.

13.

Hansch, C. In "Progress i n Photosynthesis Research", V o l . III, pp. 1685-1692, H. Metzner (ed.), Tübingen, 1969.

14.

Draber, W., Büchel, K. H., Dickoré, D . , Trebst, Α . , P i s t o r i u s , E . In "Progress i n Photosynthesis Research", V o l . I I I , pp. 1789-1795, H. Metzner (ed.), Tübingen, 1969.

15.

Draber, W., Büchel, K. H., Timmler, H., Trebst, A. In "Mechanism of Pesticide Action", ACS Symposium Series, Number 2, pp. 100-116, G. K. Kohn (ed.), Washington, D. C. 1974.

16.

Trebst, Α., Harth, Ε.

17.

Moreland, D. E., Boots, M. R. 42:53-58.

18.

Holm, R. E., S t a l l a r d , D. E . Weed

19.

Anderson, J. L., Thompson, W. W. Residue Rev. 43:167-189.

Sci.

(1972)

13:89-110.

Z. Naturforsch.

(1974) 29c:232-235.

Plant P h y s i o l . Sci.

(1974)

(1971) 22:10-14. (1973)

5 The s-Triazine Herbicides ENRICO KNUESLI

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch005

C I B A - G E I G Y Ltd., Agrochemicals Division, Basle, Switzerland

The i n v i t a t i o n to give a lecture at t h i s place under these festive circumstances i s a high p r i v i l e g e indeed. The confront­ ation with t h i s p r i v i l e g e caused concern to the speaker i n so far as a review can hardly furnish much evidence not known to such experts i n the matter as you all, Ladies and Gentlemen, are. What remains without reservation, however, i s the challenge to communicate to you something of the fascination experienced for about twenty years now on the way to and on the way with t r i a z i n e herbicides. With t h i s i n mind, allow me to r e c a l l the scene at the middle of our century. How young an art was chemical weed control then! For a long time man had evidently not f e l t himself so helpless against weeds as against other pests. It i s not by chance that neither thorns nor t h i s t l e s but mosquitoes, gadflies and grasshoppers figure in the range of the ten biblical plagues. Pyrethrum, n i c o t i n e , copper, sulfur were chemical control measures long before chemistry entered the field of weed c o n t r o l . In the late thirties, chemistry - and organic chemistry in parti­ cular - made a decisive follow-up in the field of insecticides and fungicides, while the field of herbicides was in its infancy. In the mid fifties the range of p r a c t i c a l l y - u s e d organic herbicides was dominated by phenoxyacetic acids; i n t h i s country (USA) the production of 2.4-D had geached an output of 34,000,000 pounds with a sales value of 28x10 $ out of a total herbicide market of 38x10 $ and out of a t o t a l pesticide market of 260x10 $. The range offered to interested herbicide users included, i n 1951, besides 2,4-D the O-alkyldinitrophenols, pentachlorophenol, t r i c h l o r o a c e t i c a c i d , sodium isopropylxanthate, additional chlorophenoxyacetic acids, isopropyl-N-phenylcarbamate, endothal, maleic acid hydrazide and p-chlorophenyldimethylurea. The con­ cept of a pre-emergence treatment of weeds had just been inaugu­ rated by the last- mentioned compound. 6

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Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch005

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T h i s was t h e s t a t u s when we commenced, i n 1 9 5 2 , a p r o j e c t f o r the d i s c o v e r y and t h e development o f h e r b i c i d e s and d e f o l i a n t s . The d e c i s i o n t o i n i t i a t e s u c h a p r o j e c t was t a k e n b y t h e manage­ ment o f o u r company, t h e n J.R. GEIGY L t d . , a y e a r e a r l i e r . The company h a d a t t h a t t i m e e x p e r i e n c e i n t h e f i e l d o f p h a r m a c e u t i ­ c a l s , d y e s t u f f s, i n s e c t i c i d e s , m o t h - p r o o f i n g a g e n t s , and f u n g i ­ cides. I t i s a p l e a s u r e , a n d an e x p r e s s i o n o f g r a t i t u d e , f o r me t o r e c a l l t h a t D r . Hans G y s i n was t h e i n s p i r i n g a n d e n t h u s i n g l e a d e r o f t h e p r o j e c t and t h a t Dr. A l b e r t Gast c a r e d , w i t h h i g h e x p e r t i s e , f o r a major p a r t o f t h e greenhouse and f i e l d e v a l u a ­ tion. How d i d we a t t a c k t h e p r o b l e m ? I n t h e c o n v e n t i o n a l way: b y e s t a b l i s h i n g work h y p o t h e s e s , b y s y n t h e s i z i n g , by s c r e e n i n g , b y d i s c a r d i n g many compounds.

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Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch005

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I n a f i r s t r o u n d , we t r i e d t o o b t a i n , t h r o u g h s t r u c t u r a l v a r i a t i o n o f known a c t i v e m o l e c u l e s , .new a n d s u p e r i o r b i o l o g i c a l e f f e c t s . We were p a r t i c u l a r l y i n t e r e s t e d t o c h e c k t h e c o n s e ­ quences o f t h e i s o s t e r i c r e p l a c e m e n t o f s t r u c t u r a l e l e m e n t s i n c h l o r o p h e n y l d e r i v a t i v e s as shown above. I n t h e g r e e n h o u s e , d u r i n g b i o l o g i c a l e v a l u a t i o n G 25486 showed d e f o l i a n t p r o p e r t i e s w h i c h l e d t o s t r u c t u r a l v a r i a t i o n work. However, no compound u s e f u l u n d e r p r a c t i c a l c o n d i t i o n s c o u l d be f o u n d . G 25795 d e m o n s t r a t e d r e m a r k a b l e r o o t - p r o m o t i n g a c t i v i t y s o t h a t many f u r t h e r a n a l o g u e s and homologues w e r e synthesized.

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X

N Ν -NH-i^jI-OC H 2" 5 p

G 25798

5.

KNUESLi

s-Triazine

79

Herbicides

CI

CI-

\-NH-^J-N(C H ) 2

5

2

G 2T902

Cl

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch005

G 2580U

Cl

2 5

Ν

2

5

G 258lU

G 2580U r e v e a l e d s u b s t a n t i a l h e r b i c i d a l a c t i v i t y and i n q u i t e e a r l y t e s t s a d i s t i n c t s e l e c t i v e behaviour versus corn and cotton. Why* y°u y a s k , d i d t h e y i n c l u d e , r a t h e r u n e x p e c t e d l y , t h i s s - t r i a z i n e r i n g s y s t e m ? The b a c k g r o u n d h a s a l r e a d y b e e n reported repeatedly. We knew t h a t i n t h e f i e l d o f d y e s t u f f s a n d p h a r m a c e u t i c a l s t h e s u b s t i t u t i o n o f an u r e a b r i d g e b y a b i s - a m i n o - s . - t r i a z i n e g r o u p h a d on o c c a s i o n n o t f u n d a m e n t a l l y changed t h e r e s p e c t i v e properties. m

a

Surfene NH

2 NH

CH -^ 3

Ν

γ

NH Ν

NH

•N' 2

Surfene C or Congasine Jensch,Angew.Ch. 50 891

(1937)

CH 3

PESTICIDE C H E M I S T R Y IN

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch005

80

THE

20TH C E N T U R Y

S u r f e n e shows, as an e x a m p l e , s u c h a s t r u c t u r a l c o m b i n a t i o n h a v i n g p r o t o z o i d i c i d a l a c t i v i t y , d e v e l o p e d by a German s c i e n t i s t . So we w e r e i n d u c e d t o t r y t h i s a p p r o a c h , t o o , and we s t a r t e d s y n t h e s i s w o r k i n t h e f i e l d o f £-triazines. The r e s u l t o f o u r p r i m a r y w o r k i n g h y p o t h e s i s was d i s a p p o i n t i n g ; d e r i v a t i v e s b e a r i n g a n i l i n o r a d i c a l s showed no h e r b i c i d a l e f f e c t s . S u r p r i s i n g l y , h o w e v e r , t h e h e r b i c i d a l a c t i v i t y r e a p p e a r e d i n t h e s t r u c t u r e 2c h l o r o - 4 , 6 - b i s - d i e t h y l a m i n o - j ^ - t r i a z i n e , compound G 25804 shown previously. The a w a r e n e s s t h a t we w e r e c o n f r o n t e d w i t h a com­ p l e t e l y new h e r b i c i d a l m a t r i x w i t h a p p a r e n t l y s u p e r i o r u s e f u l ­ n e s s l e d us t o i n t e n s i v e w o r k a r o u n d t h e s ^ t r i a z i n e r i n g s y s t e m . What a b e a u t i f u l t o o l i s c y a n u r i c c h l o r i d e f o r t h e c h e m i s t working i n chemical synthesis! T h r e e c h l o r i n e atoms o f f e r r e ­ a c t i o n w i t h a l a r g e p r o p o r t i o n of the chemicals l i s t e d i n the B e i l s t e i n Handbook o r t h e C h e m i c a l A b s t r a c t s I n d e x . N o t o n l y t h a t : t h e c h l o r i n e atoms a r e r e a s o n a b l e enough n o t t o r e a c t s i m u l ­ taneously but, under adequate c o n d i t i o n s , s t e p w i s e , a l l o w i n g myriads of p o t e n t i a l combinations. Furthermore: cyanuric c h l o r i d e has b e e n and i s a r e l a t i v e l y cheap k e y m a t e r i a l ; i t can be p r o d u c e d q u i t e e a s i l y f r o m s u c h b a s i c m a t e r i a l s as c h l o r i n e and h y d r o c y a n i c a c i d . As we a s s e m b l e u n d e r t h e a u s p i c e s o f t h e A m e r i c a n C h e m i c a l S o c i e t y , y o u may a s k w h e t h e r i t has n o t b e e n a b o r i n g t a s k t o d e a l w i t h t h i s c h e m i s t r y w h e r e t h e r e a c t i o n scheme i s u s u a l l y quite transparent. No d o u b t , t h e m a j o r a t t r a c t i v e n e s s has b e e n and i s t h e s t r u c t u r e / a c t i v i t y e v a l u a t i o n and t h e r e s p e c t i v e de­ ductions. B u t now and t h e n i t o c c u r r e d t h a t a r a t h e r n i c e u n e x ­ p e c t e d c h e m i c a l o f f s p r i n g r e s u l t e d f r o m t h i s w o r k , and t h e c h e m i c a l a c c e n t o f o u r m e e t i n g may j u s t i f y t h e q u o t i n g o f some examples: We i d e n t i f i e d t h e s t r u c t u r e o f a s i d e p r o d u c t o b t a i n e d i n a l i q u i d phase p r o c e s s f o r the p r o d u c t i o n of c y a n u r i c c h l o r i d e ; t h i s t e t r a m e r o f c h l o r o c y a n had n o t b e e n d e s c r i b e d b e f o r e and we studied i t s r e a c t i v i t y :

CI Ν

CI-

1

Ν

ν-

Cl Cl

We i d e n t i f i e d a y e l l o w compound w h i c h p o i s o n e d f o r a c e r ­ t a i n time the c a r b o n - c a t a l y s t i n the t r i m e r i z a t i o n of chlorocyan as c y a m e l u r i c c h l o r i d e :

5.

KNUESLi

s-Triazine

Herbicides

81

CI

Cyameluric

chloride

CI

We f o u n d t h a t

cyanuric

chloride

reacts

easily

but

controllable

manner w i t h d i m e t h y l f o r m a m i d e , CO^ b e i n g

The

was

reaction

fully

elucidated

l a t e r by

in

a

evolved.

H.Gold:

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch005

CI

c i - k > JJ-ci Ν 3 HCON(CH ) 3

2

0CHN(CH ) C1 3

[

2

Cl(CH ) NCHO-k J-OCHN(CH ) Cl ] 3

N

2

3 HCON(CH

3 C0

+

2

3

3

3*2

|^(CH ) NCH=N-CH=N(CH ) 3

2

H.Gold,

But l e t myriads

us

herbicidal

activity

under p r a c t i c a l Starting ion

return

of possible

to

to

the

3

2

problem of

956

(i960)

selecting,

dérivâtes,

9

and from t h e s e ,

CI

J

Angew.Chem. Jg

2 k,6-s-triazine

out

of

the

t h o s e which have

those which w i l l

be

useful

conditions.

from the

structure

a l o n g f o u r main l i n e s

with regard

2

the

o f G 2580U we i n i t i a t e d

i n order

biological

to

explore

characteristics:

the

variat-

consequences

82

PESTICIDE C H E M I S T R Y

IN T H E 20TH

CENTURY

G 2580U

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch005

CI

>V-<

Var.

Var..

Var.

Var.

Var.

a)

Var.

Var. Var

N ^ IΝ Ι II

•V-

Var.

Var.

Var.

1

Var.

var.-v

y-N : ^Var.

Var.

a) by v a r y i n g t h e N - a l k y l r a d i c a l s b ) b y s u b s t i t u t i n g t h e c h l o r i n e atom b y o t h e r s u i t a b l e groups c ) b y p e r m u t i n g most d i f f e r e n t r a d i c a l s on t h e t h r e e r i n g p o s i t i o n s a l l o w i n g s u b s t i t u t i o n and d) b y r e p l a c i n g t h e s - t r i a z i n e r i n g b y o t h e r N 7 h e t e r o c y c l e s m a i n l y p r o v i d e d w i t h h a l o g e n and alkylamino radicals. A f t e r h a v i n g s y n t h e s i s e d and t e s t e d many r e p r e s e n t a t i v e s we c a n c o n c l u d e now t h a t , i n g e n e r a l , t h e f o l l o w i n g c r i t e r i a must be f u l f i l l e d i n o r d e r t o o b t a i n s u b s t a n t i a l h e r b i c i d a l a c t i v i t y : - two n i t r o g e n f u n c t i o n s b o u n d t o r i n g c a r b o n atoms a r e e s s e n ­ t i a l f o r the t y p i c a l t r i a z i n e a c t i v i t y pattern. - t h e p r e s e n c e o f one t o t h r e e J L ~ l k y l s u b s t i t u e n t s i s n e e d e d , t h o s e compounds b e a r i n g one a l k y l g r o u p on e a c h n i t r o g e n function being of special interest. - a l k y l s Cj_ t o C^ a r e most s u i t a b l e , i n c l u d i n g m e t h o x y a l k y l s . - s u b s t i t u t i o n o f t h e c h l o r o atom b y a l k o x y and a l k y l t h i o g r o u p s , p r e f e r a b l y m e t h o x y and m e t h y l t h i o , c o n s e r v e s t h e h i g h h e r b i c i ­ d a l a c t i v i t y b u t l e a d s t o a change o f t h e c r o p s e l e c t i v i t y p a t ­ tern. S u b s t i t u t i o n o f t h e c h l o r o atom b y b r o m i n e , b y f l u o r i n e , b y n i t r i l o - , h y d r a z i n o - , a l k y l - , h a l o a l k y l - , a l k o x y a l k o x y groups leads very o f t e n t o remarkable h e r b i c i d a l but seldom - from t h e p r a c t i c a l point o f view - t o superior a c t i v i t y . a

5.

KNUESLi

s-Triazine

Herbicides

83

I t i s thereby obvious t o everybody a c t i v e i n t h i s f i e l d t h a t t h e q u a l i f i c a t i o n " s u p e r i o r a c t i v i t y " c a n n e v e r r e l a t e t o one parameter a l o n e ; a c t i v i t y a g a i n s t t h e t a r g e t organisms i s , o f c o u r s e , an a b s o l u t e p r e r e q u i s i t e b u t t h i s a c t i v i t y c a n , o u t s i d e t h e f i e l d o f i n d u s t r i a l weed c o n t r o l , o n l y b e made v a l u a b l e b y a complementary s u i t a b l e crop s e l e c t i v i t y p a t t e r n . The f o l l o w i n g compounds r e s u l t i n g f r o m o u r p r o j e c t r e a c h e d the l e v e l o f p r a c t i c a l use: CI

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch005

Common name:

G

27692

C H NH-

"NHC H

G

27901

C H NH-

-N(C H )

G

30027

C H NH-

-NHiC^H

ATRAZINE

G

30028

iC^H^NH-

-NHiC H

PROPAZINE

G

13528

C H NH-

-NHsec.C^H

SEBUTHYLAZINE

G

13529

C H NH-

-NH-t.C H

TERBUTHYLAZINE

2

2

2

2

2

5

2

2

5

5

5

5

SIMAZINE

5

5

TRIETAZINE

2

u

9

OCH, 1 3 N^N Common name:

G

31^35

iC^H^NH-

-NHiC^H

PROMETONE

G

32293

C H NH-

-NHiC^H

ATRATONE

GS 11+25U

C H NH-

-NHsec.C^H

SECBUMETONE (proposed)

GS 1U259

C H NH-

-NH-t.C H

TERBUMETONE (proposed)

2

2

2

5

5

5

u

9

PESTICIDE CHEMISTRY IN T H E 20TH CENTURY

84

A

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch005

Ν

3

I

Common name:

-NHC H

G

32911

G

3^161

iC^H^NH-

-NHiC^H

PROMETRYN

G

3^162

C^NH-

-NHiC^H

AMETRYN

G

3U360

-NHiC^H

DESMETRYN

G

36393

GS IU26O

CgH

HH-

CH

NH-

iC^H^NHCgH

MH-

2

SIMETRYN

5

-NHCH CH CH 0CH,

METHOPROTRYN

-NH-t.C H

TERBUTRYN

2

2

u

2

9

Common name :

GS I6068

i C H NH3

{

-NHiC H 3 Γ

DIPROPETRYN / -, \ (proposed)

They d i f f e r , o f c o u r s e , s u b s t a n t i a l l y as t o t h e i m p o r t a n c e t h e y assumed. As an example G 2 7 9 0 1 , T r i e t a z i n e , was s o l d once i n a q u a n t i t y o f a c o u p l e o f t h o u s a n d pounds f o r weed c o n t r o l i n chrysanthemums i n J a p a n and c a n , t h e r e f o r e , n o t b e p u t i n l i n e w i t h f o r example G 30027, A t r a z i n e . No r e s e a r c h g r o u p , be i t a c a d e m i c o r i n d u s t r i a l , c a n e x p e c t u n l i m i t e d e x c l u s i v i t y a f t e r having i d e n t i f i e d a f i e l d which i n ­ vites further exploitation. The c o m p i l a t i o n and a n a l y s i s o f the main c o n t r i b u t i o n s , e x p e r i m e n t a l o r s a l e s p r o d u c t s , developed b y g r o u p s o t h e r t h a n o u r s show t h e f o l l o w i n g p i c t u r e : a) Our c o n c l u s i o n t h a t i n t e r e s t i n g a c t i v i t y i s m a i n l y c o n ­ n e c t e d w i t h t h e p r e s e n c e o f two m o n o s u b s t i t u t e d amino r a d i c a l s and a h a l o g e n , h a l o g e n o i d , a l k o x y o r a l k y l t h i o g r o u p has b e e n confirmed. b ) One t e n d e n c y c i r c l e d a r o u n d t h e g r a f t i n g o f a h y d r o x y o r a l k o x y g r o u p d i r e c t l y on t h e amino f u n c t i o n o r i n t o t h e a l k y l radical:

5.

KNUESLi

s-Triazine

Herbicides

Hydroxy o r a l k o x y a l k y l DuPont

Cl

1957/1965

Monsanto

radicals:

-NHCH C H C H O C H -NHCH 2

2

2

3

_ _ ._

CHCHOCH 2

2

2

J

. ^ _ _

CH^S -NHCH^CH^CH^OCH -NHCH^CH^CH^0CH 2

1963

Allied

85

Cl

1969

2

-NHiC H 5

2

3

2

2

2

o

3

LAMBAST

ACD 15M

-NHCH OH

1

/° 3 H

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch005

BASF

Cl

-NHC H 2 5

1967

-NHCH

\ CH OCH 2

555^7 3

F u r t h e r l i n e s comprise: c ) The i n s e r t i o n o f u n c o n v e n t i o n a l a l k y l , a l k e n y l o r alkynyl substitutes. Unconventional hydrocarbon

radicals: Η

Monsanto

Λ 5

CH S -NHC H

MON 0385

1971

BASF

N» /

ci

-NHC H 2

5

3

C=CH .CH

GULF

CI

-NHiC^H

1966

CIBA 1967

3

2

CYPRAZINE

-NHCH^ V

CH S -NHC^H

BASF 5^187

-NHCH! N

1967

H

3

CH^

f 3 f 3 -NHCH—CH—CH,

DIMETHAMETRYN (proposed)

PESTICIDE C H E M I S T R Y

86

IN T H E 2 0 T H

CENTURY

d) The i n t r o d u c t i o n o f a c y l r a d i c a l s . Acylation: Matolcsy et a l . 1959/1961

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch005

Stauffer 1973

Cl

-NHiC^H

-NHCON(C H )

Cl

-NHCgH

-NHCON(CH

CI

-NHiCgH

2

5

)

2

G

- NΛ=5 COCOOC^ N

alk. DEGUSSA 1959/196U

-N:

SCC1.

alk. - N '

CH

Q

CI OCH.

CH

-NHalk.

SCH.

3

alk. \

7

'CONH

alk.

-N

X

0R

e) The i n t r o d u c t i o n o f c y a n o a l k y l r a d i c a l s . Common name :

Cyanoalkyl r a d i c a l s : Matolcsy et a l . 1959/1961

CI

-NHC^H

-NHCH CN

DEGUSSA/SHELL 1967

CI

-NHC^H

?3 -NH-C-CN

DEGUSSA/SHELL 1966

CH^S 3

2

CYANAZINE

CH3 CH3

-NHC H_ 2 5 0

-NH-C-CN I

CH

3

CYANATRINE

5.

KNUESLi

s-Triazine

Herbicides

87

Because o f t h e s u s c e p t i b i l i t y o f t h e 1 - c y a n o - l - m e t h y l e t h y l a m i n o group t o h y d r o l y s i s Cyanazine has a r e l a t i v e l y s h o r t r e s i d u a l activity. A f u r t h e r p o s s i b i l i t y o f v a r i a t i o n o f t h e non-amino p o s i ­ t i o n s i s i l l u s t r a t e d b y t h e n e x t example: V a r i a t i o n i n t h e non-amino f u n c t i o n : CH

0

I

-NHiC H

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch005

DEGUSSA 1958/62

DEGUSSA

3

T

3

-NH-C-CN I

CH.,

SCN

-NHalk.

-NHalk.

-NHalk.

-NHalk.

1959 DEGUSSA I960

SCH CN 2

The a z i d o group i s a l s o a b l e t o s u b s t i t u t e f o r o n e o f t h e two a l k y l a m i n o grouns: N^CIBA 1963

a s a r e p l a c e m e n t f o r an a l k y l a m i n o group CH S 3

-NHiC H 3

T

AZIPROTRYN

I s i t r e a l l y p o s s i b l e t o g i v e i n a few minutes condensed i n f o r m a t i o n on t h e a c t i v i t y a n d s e l e c t i v i t y p a t t e r n o f t h e t r i a z i n e h e r b i c i d e s , on t h e way t h e y a c t a n d d e g r a d e a n d on t h e i m p a c t t h e y made on w o r l d - w i d e a g r i c u l t u r e ? I s h a l l try,but not w i t h o u t d r a w i n g y o u r a t t e n t i o n t o t h e v a r i o u s r e c e n t monographs where t h e names o f t h e c o n t r i b u t o r s o f i n f o r m a t i o n a r e a l s o cited. s _ - T r i a z i n e s were a n d a r e h e r b i c i d e s w i t h a r e m a r k a b l e b r o a d spectrum o f a c t i v i t y . A t t h e same t i m e t h e y d i s p l a y s e l e c t i v i t y t o w a r d s i m p o r t a n t c r o p s . The u n i q u e , p h y s i o l o g i c a l l y b a s e d l a c k o f activity o f t h e c h l o r o t r i a z i n e s t o w a r d s c o r n a n d sorghum a n d t h e r e s u l t i n g c r o p s a f e t y r a p i d l y g a i n e d them t h e f a v o u r o f t h e growers. I n f a c t , I t h i n k i t w o u l d n o t b e immodest t o s a y t h a t c h l o r o t r i a z i n e s meant a new d i m e n s i o n i n t h e a r e a o f c o r n grow­ ing. B e s i d e s c o r n , sorghum a n d g r a p e s , c h l o r o t r i a z i n e s h a v e b e e n a p p l i e d m a i n l y i n c i t r u s , i n p i p - f r u i t s , i n ornamental and b e r r y b u s h e s a n d i n t h e f i e l d o f g e n e r a l weed c o n t r o l . Selective b e h a v i o u r c a n , o f c o u r s e , a l s o be o b s e r v e d on t h e p a r t o f c e r t a i n weeds :

PESTICIDE C H E M I S T R Y IN T H E 2 0 T H

88

CENTURY

Characteristic residual

flora:

CI birdsfoot

SIMAZINE

'-NHCH^CH.

trefoil

(Lotus

G 27692

corniculatus)

crab grass (Digitaria

sanguinalis)

ATRAZINE

CH CHgNH-

green

G 30027

foxtail

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch005

(Setaria

CHo

Ν

Ν

Increased after

stands

of wild

and o f g r e e n

treatment.

carrots

The l a s t

foxtail

show u p , f o r e x a m p l e ,

and crab

small structural

grass

t h e y were

which had developed f o r years

grass

2,^+-D t r e a t m e n t s ,

o f a new a n d d i f f e r e n t

grass-killers. a r e a p p l i e d where a h a r d t o k i l l

s u r p r i s i n g l y enough, a l s o a pronounced degrading In the series

grains

a b r o a d range

o f crops

like

cotton,

As t h e mode o f a c t i o n h a s b e e n t r e a t e d I shall

site

o f the photosystem.

i n chloroplasts

killing

of

sugarcane,

sunflowers,

small

some

action.

i n d e t a i l i n Dr.

o n l y summarize t h a t

o f t h e i n h i b i t o r m o l e c u l e seems

splitting fer

presence

system.

rice.

Moreland's paper, action

alfalfa

due t o t h e

of the a l k y l t h i o t r i a z i n e s the f i e l d

covers

weed

and sugarcanej

quite tolerant,

(under European c o n d i t i o n s ) ,

vegetables,

flora

especially

the broad a p p l i c a t i o n of Atrazine

to the build-up

f l o r a h a s t o b e c o n t r o l l e d i n woody c r o p s

application

particu­

f l o r a w h i c h c a n b e c o n t r o l l e d , h o w e v e r , b y com­

Methoxytriazines

of

consequences.

able to c o n t r o l the grass

after

I n the meantime,

l e d a t many p l a c e s

bination with suitable

is,

not amazing i n

differences?

i n t r o d u c t i o n c h l o r o t r i a z i n e s were

l a r l y welcome b e c a u s e quack-grass.

Simazine

after Atrazine

mentioned behaviour l e d t o p r a c t i c a l

At t h e time o f t h e i r

residual

carota)

of birdsfoot t r e f o i l after

Are these b i o l o g i c a l p a r t i c u l a r i t i e s

view o f the very

has

carrot

(Daucus

G 30028

Propazine treatment,

treatment

wild

PROPAZINE

3

I -NHCHCH 3

spec.)

i s , apparently,

Chlorophyll

Inhibition essential

i s thought

the exact

t o be at t h e

site

o f energy

trans­

f o r the plant

t o be t h e

of

water-

principal

5.

KNUESLi

s-Triazine

Herbicides

89

pigment i n v o l v e d i n t r i a z i n e p h y t o t o x i c i t y ; city

i n the

d a r k no

toxi-

occurs.

L o o k i n g over the whole mosaic o f f i n d i n g s r e l a t e d t o d e g r a d a t i o n , be i t i n p l a n t s , i n a n i m a l s o r i n t h e s o i l , i t comes e v i d e n t t h a t c h e m i c a l a n d b i o c h e m i c a l r e a c t i o n s o c c u r s i m i l a r s i t e s o f the t r i a z i n e molecule.

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch005

Three main pathways gradation scene: a)

Replacement (in plants,

by a h y d r o x y

de-

group

-OH

q

-SOCH.

Replacement (in

dominate the

-OH

-SCH

b)

combinations

o f the C-2 substituent animals, soils)

-CI -OCH

and t h e i r

beat

o f the

plants

and

-0H

-S0 CH 2

3

C-2 s u b s t i t u e n t

by p e p t i d e s

and a m i n o a c i d s

animals) -CI

or

-SOCH.

^C0NHCH C00H 2

-SCH CH; 2

^NHC0CH CH CHC00H 2

2

NH plants,

2

animals COOH

COOH

-SCH CH 2

0

The

search

\.

NH

f o r the

chlorotriazines S-transferase.

-SCH C H ^ NHCOCH.

/

enzyme r e s p o n s i b l e

r e s u l t e d i n the

f o r the

conjugation

i d e n t i f i c a t i o n of

a

of

glutathione

PESTICIDE C H E M I S T R Y

90

IN T H E 2 0 T H

CENTURY

c) R e a c t i o n s o f t h e N - f u n c t i o n s (in p l a n t s , animals, s o i l s ) "NHC H 2

•-NH

5

COOH -NHCH

-NHCH' V

\

'CH.

CH.

CH

f»3

f"3

I

-NH-C-C0NH

-NHCCN

I

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch005

2

C H

CH0HCH

3

\

CH.

2

-NH

O

• -NHCH' ^CH.

-NHCH CH CH OCH -

3

CH^

™3

, C H

-N

3

-NH-C-C00H

2

I

CH^

-NHCH

Q

2

2

3

•

-NHCH CH CH 0H 2

2

2

-NHCH CH C00H 2

2

-NH

-OH

T r i a z i n e t o l e r a n c e i s m a i n l y r e g u l a t e d b y t h e p a t h w a y and t h e r a t e o f d e t o x i c a t i o n i n a g i v e n p l a n t s p e c i e s . The h y d r o l y t i c and c o n j u g a t i o n p r o c e s s e s w h i c h were l i s t e d i n a ) and b ) a l l o w resistant plants t o transform the phytotoxic t r i a z i n e s rapidly i n t o non-phytotoxic metabolites. Moderately s u s c e p t i b l e p l a n t s may do t h i s more s l o w l y o r f o r example t h r o u g h N - d e a l k y l a t i o n , as l i s t e d i n c ) , whereby m e t a b o l i t e s a r e f o r m e d w h i c h may s t i l l p o s s e s s some p h y t o c i d a l a c t i v i t y . I n mammals d e g r a d a t i o n m a i n l y p r o c e e d s v i a c o n j u g a t i o n , N - d e a l k y l a t i o n and s i d e c h a i n o x i d a t i o n , l e s s by h y d r o l y s i s . Also 2-hydroxy-U-amino-6-alkylamino d e r i v a t i v e s are completely e x c r e t e d when d i r e c t l y a p p l i e d t o a n i m a l s . No o r g a n o s p e c i f i c r e t e n t i o n o r a c c u m u l a t i o n o f s - t r i a z i n e s o r m e t a b o l i t e s have been observed i n animals. I n s o i l s h y d r o l y s i s o f t h e 2 - s u b s t i t u e n t s and N - d e a l k y l a t i o n dominate t h e t r a n s f o r m a t i o n o f t h e s - t r i a z i n e s . Further degra­ d a t i o n o f t h e p r i m a r y m e t a b o l i t e s p r o c e e d s as f o l l o w s (shown b e ­ low): The d e a l k y l a t i o n s t e p s a r e r e l a t i v e l y s l o w , w h e r e a s r i n g cleavage, probably at the cyanuric a c i d stage, with the l i ­ b e r a t i o n o f C O 2 i s h i g h once ammeline i s r e a c h e d on t h e p a t h w a y :

5.

KNUESLi

s-Triazine

Herbicides

91

OH

OH

Γ ^ Ν ^ "

Ν

Η

a

l

k

y

"

l

Μ

2~^Ν^" ammeline

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch005

OH

OH

O H - ^ J - N H

alkyl

0H-^

N

J-NH

2

ammelide

OH Ν

Ν

4 J

HO-^ ^-OH

'

N

C

°2

Ν

cyanuric

It

is

interesting

amounts

of

cyanuric

two USDA s c i e n t i s t s recognized tion

as

to

note t h a t

the

presence

a c i d i n USA s o i l s

was

i n 1917; i n t h a t

case

being a step

i n the

uric

acid

of

already

certain

mentioned by

cyanuric

acid

acid allantoin

was

degrada­

cycle. Triazine

agricultural weed p r o b l e m s

herbicides sectors.

quantity-wise

the

which w i l l

top

superior technology of this

To

achievement, Esteem

evidently,

herbicides

there

class

of

create usefulness

our branch o f

a p p l i e d world-wide

i n s u c h a way a n d t o

no t e c h n o l o g y utility

are

They a r e ,

not is

be

able

such a degree

that

they

major are

used today.

Although there

is

some t i m e w i t h

a

strong

evidence

for

the

future

compounds. —

this

applied chemistry.

is

the

In the

challenge which case

of

it

w o u l d be wrong t o

a p p l a u d a few

a p p r e c i a t i o n must

go

and hundreds

important

resolve

c o n f r o n t e d at

and h i g h

hundreds

and i n to

to

of p r a c t i t i o n e r s

the

individuals.

community

and s c i e n t i s t s

w h o l e w o r l d who d e v o t e d t h e i r

interest

the

matter

i n s i g h t w h i c h we have

the

and t h e i r

of spread

the

and c o n t r i b u t e d t o

animates

successful

talents

over to

today.

92

PESTICIDE C H E M I S T R Y IN T H E 2 0 T H C E N T U R Y

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch005

No t e c h n o l o g y c a n be s u c c e s s f u l u n l e s s a p p l i e d c o r r e c t l y a n d consciously. No t e c h n o l o g y c a n be a c c e p t e d a n d j u s t i f i e d u n l e s s s u p p o r t e d by b a s i c knowledge. O n l y t h r o u g h k n o w l e d g e a r e we a b l e t o c i r c u m s c r i b e our p o s s i b i l i t i e s and our l i m i t s .

6 The Environmental Chemistry of Herbicides D O N A L D G. C R O S B Y

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch006

Department of Environmental Toxicology, University of California, Davis, Calif. 95616

One of the p r i n c i p a l problems i n discussing the environmental chemistry of herbicides lies i n deciding where to start and where to stop. As an initial o v e r s i m p l i f i c a t i o n , one could write Herbicides-->Nontoxic Inorganic Products and be close to the truth. However, the recent history of public and scientific concern over herbicide efficacy, t o x i c i t y , side­ -effects, and s i m i l a r issues requiresthat we consider at least some of the intermediate steps of that process. This consideration i s overdue, not only among herbicide chemists but p a r t i c u l a r l y among other s c i e n t i s t s and scienti­ fically-aware attorneys, public officials, managers, and even professors. Therefore, t h i s Chapter i s not so much directed toward "experts" as it is toward a more diverse and perhaps more critical audience. By "environment", I refer to the physical and chemical world which surrounds us. We usually tend to think of it in terms of "compartments"--atmosphere, s o i l (lithosphere), water (hydro­ sphere) and living plants and animals (biosphere)--although a moment's r e f l e c t i o n on soil microorganisms, airborne dust, or the clouds in the sky should tell us that t h i s categorization, too, i s oversimplified. However, the compartment concept does form a framework of chemistry by which our all-encompassing surroundings can be assigned some chemical c h a r a c t e r i s t i c s - - c h a r a c t e r i s t i c s which existed before, and exclusive of, man-made chemicals. For example, from the composition of the atmosphere, we may surmise that oxidations will represent an important group of reactions i n that compartment, ionic reactions such as nucleophilic displace­ ments should be especially important i n the hydrosphere, and so on. Unlike other pesticide groups such as the insecticides or fungicides, herbicides now encompass a very wide range of struc­ tural types ( F i g . 1). A l i p h a t i c , aromatic, and heterocyclic systems; a variety of common and less common functional groups 93

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch006

PESTICIDE C H E M I S T R Y IN T H E 2 0 T H

VIII Figure 1.

C!

Chemical structures of some important herbicides

CI 0CH C00C H 2

4

9

H^O

0CH C00H 2

CI

CI CI

C=CH Cf ^ ^ C O N H - C - C H , V)

S CH NHC-SH 3

CI

I CH,

~ CH NCS + 3

H S 2

XI Figure 2.

Typical dark reactions of 2,4-D butyl ester (III), pronamid (VI), and metham (XI)

CENTURY

6.

CROSBY

Environmental

Chemistry

of

Herbicides

95

i n c l u d i n g e s t e r s , a c i d s , a m i n e s , n i t r o compounds, a n d t h i o - a c i d s ; a continuum o f p o l a r i t i e s from w a t e r - s o l u b l e s a l t s t o hydrophobic h y d r o c a r b o n s — a l l seem t o s h a r e a common p r o p e r t y : reactivity. I t i s w i t h the c h e m i c a l consequences o f the i n t e n t i o n a l o r i n a d ­ v e r t e n t i n t r o d u c t i o n o f the t w o — r e a c t i v e h e r b i c i d e s and t h e c h e m i c a l compartments o f t h e e n v i r o n m e n t — t h a t t h i s p a p e r w i l l deal.

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch006

Interactions D e s p i t e the c h e m i c a l d i v e r s i t y o f the s e v e r a l hundred s t r u c t u r e s r e p r e s e n t i n g h e r b i c i d a l a c t i v i t y , most r e a c t i o n s o f h e r b i c i d e s f a l l w i t h i n o n l y a l i m i t e d number o f m e c h a n i s t i c t y p e s : o x i d a t i o n , r e d u c t i o n , n u c l e o p h i l i c displacements (such as h y d r o l y ­ s i s ) , e l i m i n a t i o n s , and a d d i t i o n s . "Herbicides", after a l l , are m o r e - o r - l e s s o r d i n a r y c h e m i c a l s , and t h e i r p r i n c i p a l t r a n s f o r ­ m a t i o n s i n t h e e n v i r o n m e n t a r e f u n d a m e n t a l l y no d i f f e r e n t f r o m those i n l a b o r a t o r y glassware. Figure 2 i l l u s t r a t e s three t y p i c a l examples w h i c h have r e c e i v e d t h e i r s h a r e o f c l a s s i c a l l a b o r a t o r y study—the a l k a l i n e hydrolysis of a carboxylic ester (in this case, an e s t e r o f 2,4-dichlorophenoxyacetic a c i d , I X ) , the c y c l o ­ a d d i t i o n o f a n a l c o h o l t o a n o l e f i n (as i n t h e a c e t y l e n e , V I ) , a n d t h e β-éliminâtion o f a d i t h i o c a r b a m a t e w h i c h p r o v i d e s t h e u s u a l s y n t h e t i c r o u t e t o a n i s o t h i o c y a n a t e ( c o n v e r s i o n o f a n N.Ndimethylcarbamic a c i d s a l t , XI, t o methyl isothiocyanate). Allow the s t a r t i n g m a t e r i a l s h e r b i c i d a l a c t i o n (which they have), g i v e them names s u c h a s "2,4-D e s t e r " o r " p r o n a m i d e " o r "Vapam", a n d l e t s o i l form the w a l l s o f an outdoor r e a c t i o n k e t t l e ; the r e a c ­ t i o n s a n d p r o d u c t s r e m a i n t h e same. Generally these environmental reactions i n s o i l o r water p r o c e e d r a t h e r s l o w l y compared t o what we m i g h t be u s e d t o u n d e r the f o r c i n g c o n d i t i o n s o f the l a b o r a t o r y . For example, t h e h y d r o l y s i s o f h a l f t h e 2,4-D e s t e r i n n a t u r a l w a t e r r e q u i r e s 220 d a y s a t pH 6 ( 1 ) , a n d a p p r e c i a b l e c y c l i z a t i o n o f V I t a k e s 40 d a y s i n s o i l ( 2 ) . However, r e a c t t h e y do. As s e e n f r o m T a b l e I , c o m p a r i s o n o f t h e t r a n s f o r m a t i o n r a t e s o f a number o f common h e r b i c i d e s i n s t e r i l e a n d n o n s t e r i l e s o i l c l e a r l y show t h a t s u c h n o n b i o l o g i c a l r e a c t i o n s must be a t l e a s t a s i m p o r t a n t a s metabo­ l i s m i n b r i n g i n g a b o u t f u n d a m e n t a l e n v i r o n m e n t a l changes among h e r b i c i d e s when p r o v i d e d enough t i m e . Many o f t h e s e same r e a c t i o n s a r e m a r k e d l y a c c e l e r a t e d b y t h e e n e r g y o f s u n l i g h t ( 3 ) , a n d a number a r e u n e x p e c t e d l y r a p i d . F o r e x a m p l e , a f t e r t h e 2,4-D e s t e r s a r e h y d r o l y z e d b y w a t e r a n d l i g h t (1), the r e s u l t i n g a c i d undergoes o x i d a t i o n , r e d u c t i o n , and n u c l e o p h i l i c d i s p l a c e m e n t o f r i n g - c h l o r i n e s , a t ambient tempera­ t u r e s , w h i c h w o u l d be v e r y d i f f i c u l t t o p e r f o r m u n d e r o r d i n a r y (dark) l a b o r a t o r y c o n d i t i o n s ( 4 ) . B e s i d e s l i g h t , the d e g r a d a t i o n o f t h e s e phenoxy a c i d h e r b i c i d e s r e q u i r e s a t m o s p h e r i c o x y g e n , t h e h y d r o x i d e i o n n o r m a l l y p r e s e n t i n w a t e r (10 M a t n e u t r a l i t y ) , w a t e r , a n d some e x t r a c t a b l e s o u r c e o f h y d r o g e n ( F i g . 3) ( 5 ) . The 7

96

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch006

PESTICIDE C H E M I S T R Y IN T H E 2 0 T H C E N T U R Y

CI Figure 4.

CI

Metabolism and photodecomposition products of monuron (XHI)

6.

Environmental

CROSBY

Table I.

Chemistry

97

D e g r a d a t i o n o f H e r b i c i d e s i n S t e r i l e and N o n - s t e r i l e Soil.

Sterilization Method

Herbicide

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch006

of Herbicides

Amiben ( e s t e r ) Amitrole Atrazine Bromoxynil Pronamid Dalapon Dichlobenil Diphenamid Diuron

Steam

R e l a t i v e Rate (sterile/non-sterile) 1/1 1/1

N a; N e t h y l e n e o x i d e KN3 Autoclave Steam Autoclave Autoclave Radiation Chloropicrin 3

1/1

1/10 1/1 <1/10 1/0.5 1/1.5 1/5

i m p o r t a n c e o f t h e makeup o f s u c h a n o n l i v i n g m i c r o c h e m i c a l e n v i ­ ronment t o h e r b i c i d e t r a n s f o r m a t i o n s c a n n o t b e o v e r e m p h a s i z e d ( 6 ) . Of c o u r s e , t h e b i o c h e m i c a l a c t i o n o f l i v i n g p l a n t s a n d a n i m a l s c a n n o t be d i s c o u n t e d ( T a b l e I ) a n d o f t e n r i v a l s o r e x c e e d s a b i o t i c a c t i o n . Monuron ( X I I I ) i s r e a d i l y d e g r a d e d b y m i c r o o r g a n ­ i s m s , h i g h e r p l a n t s , a n d a n i m a l s (7) b y t h e r o u t e s shown i n F i g . 4. These m e t a b o l i t e s then a r e a t l e a s t p a r t i a l l y c o n v e r t e d f u r t h e r t o o x i d i z e d p r o d u c t s , c o n j u g a t e s w i t h amino a c i d s o r c a r b o h y d r a t e s , o r o t h e r r e p r e s e n t a t i v e s o f the remarkable syn­ t h e t i c a b i l i t i e s o f organisms ( 8 ) , although they o f t e n are r e c o n v e r t e d t o t h e p a r e n t m e t a b o l i t e upon r e t u r n t o s o i l o r w a t e r . A s i g n o f the i n t e g r i t y o f environmental chemistry i s that t h e p r i m a r y m e t a b o l i t e s o f monuron, shown i n t h e F i g u r e , a r e i d e n t i c a l w i t h t h e m a j o r p r o d u c t s o f monuron p h o t o d e c o m p o s i t i o n i n w a t e r ( 9 ) ; t h e b a s i c r e a c t i o n s a n d r e a g e n t s p r o b a b l y a r e t h e same. R e c a l l t h a t t h e f i n a l f a t e o f monuron a n d o t h e r h e r b i c i d e s u n d o u b t e d l y w i l l be t h e i n o r g a n i c s t a t e — w a t e r , c a r b o n d i o x i d e , ammonia o r n i t r o g e n o x i d e s , and c h l o r i d e i o n s — b u t w i t h o u t a c o n s i s t e n t t i m e frame. I t i s t h e i n t e r m e d i a t e s t a g e s w h i c h c a n be f r u s t r a t i n g , d a n g e r o u s , u n p r e d i c t a b l e , and o c c a s i o n a l l y s c i e n t i ­ fically delightful. The D i r e c t i o n s o f E n v i r o n m e n t a l

Chemistry

W i t h t h o s e q u a l i t i e s i n m i n d , what may we e x p e c t o f t h e E n v i r o n m e n t a l C h e m i s t r y o f H e r b i c i d e s a s we e n t e r t h e "Second C e n t u r y o f A m e r i c a n C h e m i s t r y ? " P e r h a p s a g r e a t many more c o n t r i ­ b u t i o n s t o b o t h b a s i c s c i e n c e and p r a c t i c a l a r t t h a n most p e o p l e h a v e c o n s i d e r e d . By way o f e x a m p l e , I w o u l d l i k e t o m e n t i o n j u s t f o u r a r e a s : f u n d a m e n t a l c h e m i s t r y , c h e m i c a l b i o l o g y , human s a f e t y , and agronomic e f f i c a c y .

PESTICIDE C H E M I S T R Y IN

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch006

98

THE

20TH

CENTURY

R e v e a l i n g t h e S u r p r i s i n g C h e m i s t r y o f Nature» F i g u r e s 1 and 4 showed a m i n e s and t h e i r d e r i v a t i v e s t o be i m p o r t a n t e n v i r o n ­ m e n t a l b r e a k d o w n p r o d u c t s as w e l l as h e r b i c i d e s i n t h e i r own right. I n t h e l a b o r a t o r y , s u c h s u b s t a n c e s can be o x i d i z e d by t h e most p o w e r f u l a g e n t s ( e . g . , p e r o x y t r i f l u o r o a c e t i c a c i d ) t o t h e c o r r e s p o n d i n g a r o m a t i c n i t r o compounds ( 1 0 ) . However, t h e s i m p l e i l l u m i n a t i o n of at l e a s t s e v e r a l r e p r e s e n t a t i v e s i n water (pc h l o r o a n i l i n e , b e n t a z o n e , and S u s t a r ) r e s u l t e d i n d e t e c t a b l e l e v e l s o f c o r r e s p o n d i n g n i t r o d e r i v a t i v e s ( F i g . 4) ( 1 1 - 1 3 ) . What n a t u r a l o x i d a n t s a r e g e n e r a t e d w h i c h a r e b o t h r e a c t i v e enough and s t a b l e enough t o c a r r y o u t s u c h t r a n s f o r m a t i o n s ? A n o t h e r common l a b o r a t o r y r e a c t i o n o f amines i s d i a z o t i z a t i o n t o p r o v i d e u n s t a b l e and h i g h l y r e a c t i v e d i a z o n i u m s a l t s . Plimmer e t a l . ( 1 4 ) h a v e i s o l a t e d an a r o m a t i c t r i a z e n e (XV) f r o m s o i l c o n t a i n i n g 3 , 4 - d i c h l o r o a n i l i n e (XIV) and p r e s e n t e d e v i d e n c e t h a t i t i s f o r m e d by " n a t u r a l ' d i a z o t i z a t i o n o f t h e a n i l i n e f o l l o w e d by c o u p l i n g w i t h a s e c o n d amine m o l e c u l e ( F i g . 5 ) . If this i s t r u e — t h a t t h e n a t u r a l n i t r i t e commonly f o u n d i n s o i l and w a t e r c a n b r i n g a b o u t d i a z o t i z a t i o n — a new d i m e n s i o n must be added t o b o t h t h e n a t u r a l mechanisms o f h e r b i c i d e d e g r a d a t i o n and t h e g e n e r a t i o n o f new s e r i e s o f p o t e n t i a l l y d a n g e r o u s t r a n s f o r m a t i o n products. P h o t o d e c o m p o s i t i o n o f a s u b s t a n c e p r e v i o u s l y has been considered to r e q u i r e the p r i o r a b s o r p t i o n of l i g h t — t h e f i r s t r u l e o f p h o t o c h e m i s t r y . Y e t , f i r s t e t h y l e n e t h i o u r e a (15) and more r e c e n t l y m o l i n a t e ( I I ) , compounds w h i c h do n o t a b s o r b u l t r a v i o l e t l i g h t i n t h e s u n l i g h t w a v e l e n g t h r a n g e , were o b s e r v e d t o u n d e r g o photooxidation i n s t e r i l i z e d f i e l d water ( F i g . 6). Through the w o r k o f R o s s ( 1 6 ) , we now know t h a t n a t u r a l w a t e r s c o n t a i n p h o t o o x i d a n t s ( j u s t as t h e a t m o s p h e r e d o e s ) w h i c h c a u s e o x i d a t i v e d e g r a d a t i o n o f h e r b i c i d e s e v e n t h o u g h no l i g h t i s a c t u a l l y a b s o r b e d by t h e p e s t i c i d e . P r o v i d i n g I n s i g h t Into the Chemical B a s i s of P l a n t Processes. A wide v a r i e t y of carbamates, t r i a z i n e s , amides, ureas, quinones and o t h e r h e r b i c i d e s a r e known t o e x e r t t h e i r a c t i o n by i n h i b i t i n g the p l a n t ' s p h o t o s y n t h e t i c process (17). However, some o f t h e same compounds h a v e b e e n u s e d v e r y e f f e c t i v e l y as p r o b e s i n t o t h e p a t h w a y s o f p h o t o s y n t h e s i s and e l e c t r o n t r a n s p o r t i n p l a n t s . The p h o t o s y n t h e t i c p r o c e s s c o n s i s t s o f two c h l o r o p h y l l m e d i a t e d , l i g h t - e n e r g i z e d s y s t e m s , an e l e c t r o n - t r a n s p o r t s y s t e m b r i d g i n g them, and t h e " d a r k - r e a c t i o n " i n w h i c h l i g h t - g e n e r a t e d ATP and NADPH r e d u c e c a r b o n d i o x i d e t o c a r b o h y d r a t e . The l o c u s o f a c t i o n o f t h e p r i n c i p a l h e r b i c i d a l i n h i b i t o r s has b e e n a s c e r t a i n e d i n a number o f i n s t a n c e s ( F i g . 7 ) , b u t , w i t h few e x c e p t i o n s , t h e e x a c t c h e m i c a l mechanism by w h i c h i n h i b i t i o n t a k e s p l a c e r e m a i n s unknown. As more h e r b i c i d e s a r e examined and more i s l e a r n e d o f s t r u c t u r e - a c t i v i t y r e l a t i o n s , an i n c r e a s i n g l y d e t a i l e d p i c t u r e o f t h e c h e m i s t r y by w h i c h l i g h t e n e r g y g e n e r a t e s c h e m i c a l s v i a "photosynthesis" i s assured. However, i n a number o f i n s t a n c e s , b o t h t h e f u n d a m e n t a l b i o ­ c h e m i s t r y and i t s e x t e n s i o n t o t h e s e a r c h f o r i m p r o v e d h e r b i c i d e 1

6.

Environmental

CROSBY

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch006

Figure

5.

Chemistry

99

Formation of bis(3,4-dichlorophenyl)1,3-triazene in soil

I

C

of Herbicides

N-C-SC H 2

OO

5

_

C

0 O 0 Ο II

Ί

N-C-SC H

II

1

N-C-SC H 2

2

3

5

Ο Figure 6.

>

Photodecomposition of molinate (II) in water

H 0 9

NADP Plasto-

Plasto-

Ferre-

/"

2

ϋ ,Η 2

γ—quinone ». c y a n » Ζ —^.doxin —,ί A etc. etc. Α I I I HYDRAUREAS BIPYRIDYLIUMS ZONES ANILIDES QUINONES Figure 7.CARBAMATES Effects of herbicides on photosynthetic processes TRIAZINES

A

NADPH

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch006

100

PESTICIDE C H E M I S T R Y IN

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c a n d i d a t e s w i l l depend upon p r i o r i n v i v o e n v i r o n m e n t a l t r a n s f o r ­ m a t i o n s — t h e r e a c t i v e ( t o x i c ) f o r m w i t h i n t h e p l a n t i n d e e d may not be i d e n t i c a l t o t h e more s t a b l e one a p p l i e d . F o r e x a m p l e , most o f t h e s p e c t a c u l a r a c t i o n o f p a r a q u a t ( V I I I ) on p l a n t s a c t u a l l y a p p e a r s due t o t h e i n s i t u g e n e r a t i o n o f t o x i c h y d r o g e n p e r o x i d e ( 1 8 ) , d i p h e n a t r i l e a l m o s t c e r t a i n l y i s c o n v e r t e d t o i t s amide o r a c i d b e f o r e a c t i o n ( 1 9 ) , and t h e a c t i v a t i o n o f phenoxy h e r b i c i d e s by m e t a b o l i s m t o c h l o r o a c e t i c a c i d has been p r o p o s e d ( 2 0 ) . P l a n t s o b v i o u s l y h a v e mechanisms by w h i c h t o r e s i s t d i s e a s e , but i t i s l a r g e l y through the study of h e r b i c i d e s t h a t other p l a n t d e f e n s e mechanisms h a v e b e e n r e v e a l e d . D e t o x i c a t i o n as a d e f e n s e a g a i n s t f o r e i g n c h e m i c a l s i s now g e n e r a l l y a c c e p t e d t o h a v e m a j o r importance f o r h e r b i c i d e s e l e c t i v i t y . Resistant species display a b i l i t i e s f o r o x i d a t i o n , r e d u c t i o n , h y d r o l y s i s , and conjugation a l m o s t u n r e c o g n i z e d a d e c a d e ago ( 8 , 2 1 ) . However, one e s p e c i a l l y i n t r i g u i n g mechanism i s t h a t w h i c h c a u s e s m a i z e t o be r e s i s t a n t t o i n t o x i c a t i o n by s i m a z i n e ( X V I ) . In t h i s i n s t a n c e , the p l a n t c o n t a i n s a n a t u r a l but v e r y r e a c t i v e n u c l e o p h i l e , 2,4-dihydroxy-7methoxy-l,4-benzoxazin-2-one (XVII) which d i s p l a c e s c h l o r i d e from the r e a c t i v e c h l o r o t r i a z i n e ( F i g . 8 ) ; the r e s u l t i n g O - s u b s t i t u t e d h y d r o x y l a m i n e i s much more s u s c e p t i b l e t o h y d r o l y s i s t h a n was the s i m a z i n e , and t h e b e n z o x a z i n o n e i s r e g e n e r a t e d a l o n g w i t h n o n ­ t o x i c hydroxysimazine X V I I I (22,23). The d e g r a d a t i o n p r o c e s s e s w i t h i n p l a n t s s t i l l p r o v i d e a s o u r c e o f amazement f o r me, e x p e c i a l l y when s u c h s u p p o s e d l y " s i m p l e " organisms r o u t i n e l y c a r r y out c h e m i c a l r e a c t i o n s w h i c h a c h e m i s t i s h a r d p u t t o do i n h i s l a b o r a t o r y . These a b i l i t i e s a l s o may e v e n t u a l l y p r o v i d e some k e y s i n t o t h e f u n d a m e n t a l b i o c h e m i c a l p r o c e s s e s s h a r e d by a l l l i v i n g t h i n g s . The r e l a t i v e l y s t r e n u o u s o x i d a t i o n o f an a r o m a t i c amine t o t h e c o r r e s p o n d i n g n i t r o compound was m e n t i o n e d e a r l i e r ; h o w e v e r , b e a n p l a n t s can c o n v e r t t h e u r e a h e r b i c i d e d i u r o n (V) i n t o 3 , 4 - d i c h l o r o n i t r o b e n z e n e (24). Unlike t h e i r halogenated r e l a t i v e s , t r i f l u o r o m e t h y l groups a t t a c h e d to a r o m a t i c r i n g s are h y d r o l y z e d t o a c i d s o n l y under extreme l a b o r a ­ t o r y c o n d i t i o n s ; c a r r o t s c o n v e r t the t r i f l u o r o m e t h y l group of t r i f l u r a l i n (IV) to the c o r r e s p o n d i n g a c i d at ambient temperature (25) . I n v e s t i g a t i o n of the photochemical degradation of t r i f l u r a l i n (26) d e m o n s t r a t e d t h e f o r m a t i o n o f b e n z i m i d a z o l e s and t h e i r i n t e r ­ mediate dihydroxybenzimidazolines t h r o u g h what i n i t i a l l y must be a f r e e - r a d i a l mechanism ( F i g . 9 ) . Yet i n v e s t i g a t i o n o f the f a c i l e p l a n t metabolism of such d i n i t r o a n i l i n e h e r b i c i d e s r e v e a l s the same o r a n a l o g o u s p r o d u c t s . Can p l a n t s use s u c h r a d i c a l r e a c t i o n s in detoxication activities? I f s o , how a r e t h e r a d i c a l s g e n e r a t e d and c o n t r o l l e d ? I f n o t , what o t h e r mechanisms m i g h t a c c o u n t f o r these p e c u l i a r t r i f l u r a l i n metabolites? The o b s e r v a t i o n has b e e n made b e f o r e (8) t h a t m e t a b o l i t e s and p h o t o p r o d u c t s o f t e n t u r n o u t t o be i d e n t i c a l . A g a i n , why? Obviously, p l a n t s d i f f e r widely i n t h e i r a b i l i t y to r e s i s t and d i s p o s e o f o t h e r w i s e t o x i c s u b s t a n c e s . M i g h t i t be p o s s i b l e

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch006

6.

CROSBY

Environmental

Figure 8.

Chemistry

of

Herbicides

Mechanism of simazine (XVI) detoxication in corn

Figure 9.

Photodecomposition of trifluralin (IV)

101

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PESTICIDE C H E M I S T R Y IN

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t o u s e h e r b i c i d e s as t a x o n o m i c p r o b e s ? I n r e c e n t y e a r s , t h e f i e l d o f b i o c h e m i c a l s y s t e m a t i c s has d e v e l o p e d r a p i d l y ( e . g . , 2 7 ) , b a s e d l a r g e l y on s t r u c t u r a l a n a l o g i e s among a l k a l o i d s , t e r p e n e s , c y a n o g e n i c g l y c o s i d e s , e t c . S t i l l , t h e v a r i e t y o f d e t o x i c a t i o n mechan­ isms demonstrated w i t h i n the p l a n t kingdom suggests t h a t a b i l i t y t o d e f e n d a g a i n s t c h e m i c a l s t r e s s had e v o l u t i o n a r y v a l u e l o n g b e f o r e t h e a d v e n t o f modern-day c h e m i c a l s and t h a t p r e s e n t t a x a must be t h e c u r r e n t p r o d u c t o f t h o s e eons o f c o p i n g w i t h an h o s t i l e e n v i r o n m e n t . F o r e x a m p l e , r e d c u r r a n t s ( R i b e s rubrum) o x i d i z e d o v e r h a l f o f an a p p l i e d d o s e o f 2,4-D and t o l e r a t e d t h e h e r b i c i d e , w h i l e t h e s u s c e p t i b l e b l a c k c u r r e n t s (R. n i g r u m ) f a i l e d a l m o s t c o m p l e t e l y a t t h e d e t o x i c a t i o n ( 2 8 ) . How does t h e g e n e t i c h i s t o r y of these v e r y s i m i l a r p l a n t s account f o r t h i s s p e c i e s s p e c i f i c i t y and how c o u l d s u c h i n f o r m a t i o n be u s e d t o p r e d i c t e f f e c t s of other h e r b i c i d e s ? P r o t e c t i n g Human W e l l - b e i n g . The g r o w i n g p o p u l a r i t y o f h e r b i c i d e s and p l a n t g r o w t h r e g u l a t o r s i s n o t a c c i d e n t a l . The proven v a l u e of these agents f o r crop p r o d u c t i o n , h e a l t h , commerce, f o r e s t r y , and many o t h e r a r e a s has c a u s e d t h e use o f p l a n t - c o n t r o l c h e m i c a l s t o d o u b l e i n t h e p a s t 10 y e a r s . Of c o u r s e , t h e f a c t t h a t a s u b s t a n c e i s u s e f u l l y t o x i c a g a i n s t a weed does n o t p r e c l u d e t o x i c e f f e c t s on d e s i r a b l e p l a n t s , h i g h e r a n i m a l s , o r e v e n on man h i m s e l f ( T a b l e I I ) . W i s e l y , s o c i e t y i s demanding a c e r t a i n amount o f a s s u r a n c e t h a t t h e t o x i c i t y o f e n v i r o n m e n t a l c h e m i c a l s be h a r n e s s e d .

Table I I .

A c u t e T o x i c i t y o f Common H e r b i c i d e s ( 2 9 ) .

Common Name D i n i t r o c r e s o l (DNOC) A l l y l alcohol Sodium p e n t a c h l o r o p h e n a t e Paraquat ( c h l o r i d e ) 2,4-D Molinate 2,4-D b u t y l e s t e r Metham Nitrofen Atrazine Diuron Trifluralin Pronamid Acute r a t

oral

toxicity.

Structure

VIII IX II III X I VII V IV VI

T r a d e Name

LD (mg/kg)

S inox

30 64 78 157 375 501 620 820 2630 3080 3400 3700-10,000 8350

Dowicide G Gramoxone Weedone 638 Ordram E s t e r o n 76 Vapam Tok Aatrex Karmex Treflan Kerb

50

a

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Chemistry

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What happens t o h e r b i c i d e s a f t e r t h e y a r e a p p l i e d ? A p r o p o r ­ t i o n w i l l be t a k e n up b y p l a n t s and e i t h e r s t o r e d o r m e t a b o l i z e d ( b i o c h e m i c a l l y t r a n s f o r m e d t o o t h e r s u b s t a n c e s , a s we have s e e n ) . The m e t a b o l i t e s , a s w e l l a s t h e r e m a i n i n g p a r e n t a n d o t h e r b r e a k ­ down p r o d u c t s , e v e n t u a l l y w i l l r e a c h w a t e r and s o i l ( 6 ) , f r o m w h i c h t h e y may v o l a t i l i z e i n t o t h e a t m o s p h e r e o r move on s u s p e n d e d d u s t o r s i l t [sometimes f o r g r e a t d i s t a n c e ( 3 0 ) ] e v e n t u a l l y t o decompose o r be r e t u r n e d t o e a r t h i n a n e v e r - d i m i n i s h i n g c y c l e . How t h e c h e m i c a l s move a n d b r e a k down i n c r e a s i n g l y d e t e r m i n e a grower's r e l a t i o n s w i t h h i s n e i g h b o r s , h i s customers, and h i s governments. MCPA a p p l i c a t i o n t o r i c e p r o v i d e s an e x a m p l e . T h i s phenoxy h e r b i c i d e ( 2 - m e t h y l - 4 - c h l o r o p h e n o x y a c e t i c a c i d ) h a s been o f v i t a l i m p o r t a n c e t o C a l i f o r n i a ' s r i c e p r o d u c t i o n f o r a number o f y e a r s , and i t s volume f o r t h a t p u r p o s e r e g u l a r l y h a s e x c e e d e d 1 0 k g / y r . However, a s MCPA i s a p p l i e d a f t e r t h e f i e l d s a r e f l o o d e d a n d t h e r i c e s e e d l i n g s have emerged, t h e r e h a s been i n c r e a s i n g c o n c e r n t h a t i t m i g h t c o n c e n t r a t e i n t h e r i c e g r a i n , move i n a i r a n d w a t e r , a n d e v e n t u a l l y e x e r t t o x i c e f f e c t s on p e o p l e o r on o t h e r crops. C a r e f u l a n a l y s i s o f MCPA's e n v i r o n m e n t a l c h e m i s t r y ( 3 1 ) shows t h a t a s l o n g a s t h e f i e l d w a t e r i s h e l d f o r a f e w d a y s , t h e MCPA d o e s n o t move a n d i s decomposed t o h a r m l e s s p r o d u c t s b y s u n ­ l i g h t and microorganisms as w e l l as by t h e r i c e p l a n t i t s e l f . Y e t , h e r b i c i d e s o r t h e i r b y - p r o d u c t s c a n be h a z a r d o u s . P e r h a p s t h e most renowned example i s t h e e x t e n s i v e l y - u s e d 2,4,5-T ( 2 , 4 , 5 - t r i c h l o r o p h e n o x y a c e t i c a c i d ) , o r r a t h e r t h e 2,3,7,8t e t r a c h l o r o d i b e n z o - p - d i o x i n (TCDD) i m p u r i t y w h i c h sometimes accompanies i t . D u r i n g massive use o f t h e h e r b i c i d e as a d e f o l i ­ a n t i n t h e V i e t n a m w a r , TCDD was f o u n d a l m o s t b y a c c i d e n t t o be one o f t h e most t o x i c s y n t h e t i c s u b s t a n c e s e v e r t e s t e d . Soon, i t was shown t o be p r e s e n t i n d o m e s t i c 2,4,5-T a s w e l l a s i n t h e chemical warfare agents. Tests i n l a b o r a t o r y animals demonstrated t h a t some o f t h e o b s e r v e d l e v e l s i n d e e d were q u i t e h i g h enough t o cause t o x i c e f f e c t s ( 3 2 ) . M i r a c u l o u s l y , f e w human t r a g e d i e s have d e f i n i t e l y been t r a c e d t o 2,4,5-T o r TCDD, i n w a r o r p e a c e . F u r t h e r i n v e s t i g a t i o n i n d i c a t e s t h a t e n v i r o n m e n t a l break-down may be l a r g e l y t h e r e a s o n . TCDD i s v e r y u n s t a b l e t o s u n l i g h t when i t i s p r e s e n t a s a t r a c e c o n t a m i n a n t i n c o m m e r c i a l p e s t i c i d e s ( F i g . 10) ( 3 3 , 3 4 ) , e s p e c i a l l y when a p p l i e d t o i n e r t s u r f a c e s o r l e a v e s . The p r e s e n t l a c k o f e v i d e n c e f o r w i d e s p r e a d o c c u r r e n c e o f TCDD i n t h e e n v i r o n m e n t may be d i r e c t l y r e l a t e d t o i t s e n v i r o n m e n t a l c h e m i s t r y . The k n o w l e d g e t h a t t h e d e t o x i c a t i o n and l o s s o c c u r through r e d u c t i v e d e c h l o r i ­ n a t i o n b y t h e s o l v e n t a l s o opens t h e way f o r i n t e n t i o n a l TCDD d e s t r u c t i o n o r decontamination. Maximizing Herbicide U t i l i t y . Most h e r b i c i d e s d i s s i p a t e rather rapidly after application. That i s , they v o l a t i l i z e , a r e decomposed b y l i g h t o r m i c r o o r g a n i s m s , a n d a r e l e a c h e d i n t o s o i l , etc. I n a n y c a s e , t h e y become u n a v a i l a b l e t o p e r f o r m t h e i r function. U l t i m a t e l y , t h i s d i s s i p a t i o n becomes d e s i r a b l e i n t h a t

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5

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2

4 Hours

Figure 10. Rates of Τ CDD photodecomposition on soil (Q), leaves Δ λ and glass (A). Closed sym­ bols represent dark controls.

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i t prevents a buildup o f p o t e n t i a l l y toxic chemicals, but the p e s t - c o n t r o l e f f i c i e n c y o f many h e r b i c i d e a p p l i c a t i o n s i s l o w because o f i t . O n l y i n r e c e n t y e a r s have we begun t o u n d e r s t a n d s o m e t h i n g a b o u t t h e d i s s i p a t i n g f o r c e s — f o r example t h e p h o t o c h e m i c a l l y - g e n e r a t e d o x i d a n t s o r p l a n t metabolism mentioned earlier. A l o t o f h e r b i c i d e h a s been w a s t e d . In o r d e r t o minimize waste as w e l l as t o d i r e c t s e l e c t i v i t y , a number o f a p p r o a c h e s t o w a r d d i s s i p a t i o n - c o n t r o l a r e b e i n g examined. F o r example, b o t h v o l a t i l i z a t i o n and p h o t o d e c o m p o s i t i o n o f t e n c a n be r e g u l a t e d t o a d e s i r e d d e g r e e by i n c o r p o r a t i o n o f a n o n - v o l a t i l e r e s i n a d d i t i v e i n t o the p e s t i c i d e f o r m u l a t i o n (35). The t e c h n i q u e a p p e a r s p r o m i s i n g f o r i n s e c t i c i d e s , a n d t h e r e i s no r e a s o n t o b e l i e v e i t s h o u l d not work f o r h e r b i c i d e s a l s o . Another a p p r o a c h i s i n h i b i t i o n o f m i c r o b i a l b r e a k - d o w n ; f o r e x a m p l e , Nm e t h y l c a r b a m a t e i n h i b i t o r s o f h y d r o l y t i c enzymes, s u c h a s PCMC (£-chlorophenyl N - m e t h y l c a r b a m a t e ) , a p p l i e d t o g e t h e r w i t h a h e r b i ­ c i d e such as chloropropham [ i s o p r o p y l N-(3-chlorophenyl)carbamate] w h i c h i s i n a c t i v a t e d b y s o i l m i c r o b e s , more t h a n d o u b l e d t h e e f f e c t i v e n e s s (36,37). However, c o n t r o l l e d o r s p e c i f i c e n v i r o n m e n t a l d e g r a d a t i o n sometimes i s n e c e s s a r y f o r h e r b i c i d a l a c t i o n . F o r example, t h e phenoxy h e r b i c i d e s e s o n e ( s o d i u m 2 , 4 - d i c h l o r o p h e n o x y e t h y l s u l f a t e ) has no e f f e c t on p l a n t s u n t i l i t c a n be o x i d i z e d t o 2,4-D b y a s p e c i f i c s o i l m i c r o o r g a n i s m , B a c i l l u s c e r e u s ( 3 8 ) . The g r o w t h r e g u l a t o r e t h o p h o n ( E t h r e l ) r e l i e s upon s l o w e n v i r o n m e n t a l c o n v e r ­ s i o n i n t o e t h y l e n e f o r i t s a c t i v i t y ( 3 9 ) . And metham (Vapam) depends upon h y d r o l y s i s i n s o i l t o r e l e a s e t o x i c m e t h y l i s o t h i o cyanate (40). S u r e l y , many s u c h common r e a c t i o n s c o u l d be u t i l i z e d f o r t h e i n t e n t i o n a l d e s t r u c t i o n o f unwanted h e r b i c i d e s a n d t h e i r r e s i d u e s ( 4 1 ) . Metham m i g h t be c a u s e d t o r e a c t s i m p l y w i t h aqueous ammonia t o f o r m h a r m l e s s m e t h y l t h i o u r e a ; many h e r b i c i d e s i n c l u d i n g p r o m e t r y n e a n d m e t r i b u z i n ( S e n c o r ) m i g h t be d e g r a d e d b y d i l u t e h y p o c h l o r i t e ( " c h l o r i n a t e d l i m e " ) o f the type used t o p u r i f y swimming p o o l s , a n d t h e p h o t o d e c o m p o s i t i o n o f o t h e r s ( s u c h a s 2,4,5-T) m i g h t b e a c c e l e r a t e d b y cheap n o n t o x i c p h o t o s e n s i t i z e r s s u c h a s a c e t o n e ( T a b l e I I I ) ( 4 2 ) . The v a r i a t i o n s o f e n v i r o n m e n t a l c h e m i s t r y a p p l i c a t i o n s t o c o n t r o l and d i r e c t h e r b i c i d e p e r s i s t e n c e and e f f e c t i v e n e s s now a p p e a r e n d l e s s . What Can We Do F o r c e n t u r i e s , p e o p l e have o b s e r v e d t h e t r a n s p o r t a n d t r a n s ­ f o r m a t i o n s o f c h e m i c a l s i n the environment w i t h o u t r e a l l y t h i n k i n g i n t e r m s o f " e n v i r o n m e n t a l c h e m i s t r y " . The o d o r o f f l o w e r s ( o r o f s t o c k y a r d s ) , t h e F a l l c o l o r a t i o n o f maple l e a v e s , a n d t h e b l e a c h i n g o f f a b r i c s were a l l t a k e n f o r g r a n t e d . Even i n t o t h e Age o f C h e m i s t r y , no one r e a l l y w o r r i e d much a b o u t where t h e smoke went o r why t h e w a t e r t a s t e d f u n n y . That h a s changed.

106

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Table I I I .

20TH

CENTURY

S e n s i t i z e d P h o t o l y s i s o f 2,4,5-T ( 4 2 ) .

Sensitizer

None None Acetone (0.4%) Acetone (0.4%) R i b o f l a v i n (5 mg/1) R i b o f l a v i n (5 mg/1) Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch006

THE

Sunlight _

+ -

+ -

+

2,4,5-T C o n c e n t r a t i o n % Loss 48 H r s 0 Hrs (mg/1) (mg/1) 1.00 1.00 1.00 1.00 1.00 1.00

0.93 0.86 0.98 0.20 0.84 0.20

7 14 2 80 16 80

S t i l l , o u r k n o w l e d g e o f t h e f o r c e s and r e a g e n t s w h i c h a c t on c h e m i c a l s i n the environment i s l a r g e l y rudimentary. However, t h r o u g h t h e i r s t r u c t u r a l v a r i e t y and g r o w i n g u s e , h e r b i c i d e s a c t as s o c i a l l y - a c c e p t a b l e c h e m i c a l p r o b e s i n t o t h a t e n v i r o n m e n t ; e n v i r o n m e n t a l d a t a on them c o u l d be i n v a l u a b l e f o r p r e d i c t i n g t h e m o b i l i t y and f a t e o f much more t o x i c , p e r s i s t e n t , and c o n s e q u e n t l y d a n g e r o u s s u b s t a n c e s w h i c h s o c i e t y r e l e a s e s d a i l y w i t h so l i t t l e k n o w l e d g e o f what becomes o f them. A r i c e - f i e l d o r a c o r n p a t c h c a n be v i e w e d a s a c h e m i c a l r e a c t o r f u l l o f r e a g e n t s i n t o w h i c h i s i n j e c t e d a s t r u c t u r a l l y u n i q u e i n d i c a t o r . The e n v i r o n m e n t a l c h e m i s t r y o f h e r b i c i d e s i s t h e r e t o s t u d y , and t h e t e s t t u b e i s as c l o s e as your f r o n t p o r c h . When t h e A m e r i c a n C h e m i c a l S o c i e t y was f o u n d e d i n 1876, no more t h a n h a l f a d o z e n w e e d - k i l l e r s w e r e i n use ( 4 3 ) . I n 1936, 60 y e a r s l a t e r , t h a t number s t i l l r e m a i n e d a l m o s t unchanged. There now a r e o v e r 200 h e r b i c i d e s and o t h e r p l a n t g r o w t h r e g u l a t o r s i n common u s e , b u t t h e w o r l d r e q u i r e m e n t s f o r f o o d , f i b e r , and f o r e s t p r o d u c t s — t h e p r i n c i p a l b e n e f i c i a r i e s o f h e r b i c i d e s — n e v e r were greater. S t i l l , t h e p u b l i c i s s a y i n g c l e a r l y t h a t i t must know what happens t o a l l t h e s e c h e m i c a l s and what some o f t h e c o n s e ­ q u e n c e s w i l l be. P e r h a p s i r o n i c a l l y , i t was a herbicide—aminotriazole—which s t a r t e d t h e p r e s e n t r e g u l a t o r y t r e n d and r e s u l t e d most r e c e n t l y i n r a t h e r s p e c i f i c government demands f o r e n v i r o n m e n t a l c h e m i s t r y d a t a t o p e r m i t t h e r e g i s t r a t i o n o f new h e r b i c i d e s and r e r e g i s t r a t i o n o f o l d f a v o r i t e s ( 4 4 ) . Modern s o c i e t y i s b e i n g pushed i n e x o r a b l y t o w a r d a most s e r i o u s d i l e m m a : t h e r e q u i r e m e n t f o r p e s t c o n t r o l v s t h e need f o r human and e n v i r o n m e n t a l s a f e t y . As we h a v e s e e n i n j u s t t h e few e x a m p l e s o f t h i s C h a p t e r , m u c h — perhaps m o s t — o f our u n c e r t a i n t y a r i s e s from ignorance of the f o r c e s w h i c h a c t upon c h e m i c a l s i n t h e e n v i r o n m e n t . Time i s grow­ i n g s h o r t f o r c h e m i s t s t o l e a r n and a p p l y t h e s c i e n t i f i c fundamen­ t a l s o f t h e p h o t o c h e m i c a l , m i c r o b i a l , and t r a n s p o r t i v e phenomena w h i c h h a v e b e e n o b s e r v e d f o r c e n t u r i e s t o i n f l u e n c e us and o u r environment.

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J u s t how s h o r t t h a t t i m e i s , i s b e i n g f e l t b y r e g u l a t o r y a g e n c i e s f a c e d w i t h s e t t i n g c r i t e r i a and e f f i c i e n t l y (and s a f e l y ) reregis­ t e r i n g most e x i s t i n g p e s t i c i d e s . Y e t , r e c e n t l y p r o v i d e d a prime o p p o r t u n i t y t o a c q u i r e some o f t h e most u r g e n t d a t a , t h e EPA f a i l e d to a c t ; s u r e l y , the burgeoning burden o f r e g i s t r a t i o n d e c i s i o n s must p o i n t t o w a r d a b a s i c n e e d f o r e n v i r o n m e n t a l chemistry p r e d i c t a b i l i t y — s o o n . I n d u s t r y , t o o , needs t h a t f u n d a ­ m e n t a l k n o w l e d g e t o f i n d s a f e r , more e f f e c t i v e p r o d u c t s . A s we now s e e , t h e e n v i r o n m e n t a l c h e m i s t r y o f h e r b i c i d e s o f t e n p r o v i d e s t h e k e y t o s e l e c t i v i t y , p e r s i s t e n c e , r e s i d u e d i s t r i b u t i o n , and mode o f a c t i o n ; r e g i s t r a t i o n r e q u i r e m e n t s f o r new d a t a a c t u a l l y may b e l o o k e d upon a s a n o p p o r t u n i t y t o a p p l y t h e demanded d a t a t o w a r d f i n d i n g new c o m p o u n d s , new f o r m u l a t i o n s , and new c o n t r o l methods r a t h e r t h a n o n l y a s an e x p e n s i v e c h o r e . A t the l e a s t , u n i v e r s i t i e s must s t a r t t o t e a c h t h e s u b j e c t t o o u r n a t i o n ' s future chemists. I am c o n v i n c e d t h a t t h e e n v i r o n m e n t a l c h e m i s t r y o f h e r b i c i d e s p r o v i d e s f o r t h e i r s a f e r and more e f f i c i e n t u s e , l e s s c o s t t o c o n s u m e r s , more b e n e f i t s t o i n d u s t r y , and e x c i t i n g a d v a n c e s i n basic science. Look around y o u : i n the next century of American C h e m i s t r y , t h i s new f i e l d o f w o r k w i l l a f f e c t e a c h o f us more t h a n we c o u l d e v e r h a v e i m a g i n e d .

Literature Cited (1) Zepp, R.G., Wolfe, N . L . , Gordon, J.Α., Baughman, G.L., Environ. Sci. Technol. 9, 1144 (1975). (2) Yih, R.Y., Swithenbank, C., McRae, D.H., Weed Sci. 18, 604 (1970). (3) Crosby, D.G., in "Herbicides: Chemistry, Degradation, and Mode of Action" (P.C. Kearney, D.D. Kaufman, e d s . ) , Vol. 2, p. 835, Marcel Dekker, New York, 1976. (4) Crosby, D.G., Tutass, H . O . , J.Agr. Food Chem. 14, 596 (1966). (5) Crosby, D.G., Wong, A.S., J. A g r . Food Chem. 2 1 , 1049 (1973). (6) Crosby, D.G., in "The Physiology and Biochemistry of Herbi­ cides" (L.J. Audus, e d . ) , 2nd Ed., Academic Press, London, 1976. (7) Menzie, C.M., "Metabolism of Pesticides", Spec. Sci. Rept: Wildlife 184, Fish and Wildlife Service, USDI, Washington, D . C . , 1974. (8) Crosby, D . G . , Ann. Rev. Plant Physiol. 24, 567 (1973). (9) Crosby, D . G . , Tang, C.-S., J. A g r . Food Chem. 17, 1041 (1969). (10) Emmons, W.D., J. Am. Chem. Soc. 79, 5528 (1957). (11) Crosby, D . G . , L e i t i s , Ε . , unpublished, 1973. (12) N i l l e s , G.P., Zabik, M.J., J. A g r . Food Chem. 22, 684 (1974). (13) M i l l e r , G., Crosby, D . G . , unpublished d a t a , 1976. (14) Plimmer, J.R., Kearney, P.C., Chisaka, Η . , Yount, J.B., Klingebiel, U . I . , J. A g r . Food Chem. 18, 859 (1970). (15) Ross, R.D., Crosby, D . G . , J. A g r . Food Chem., 2 1 , 335 (1973).

108 (16) (17) (18) (19) (20) (21) (22) (23) (24)

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(25) (26) (27) (28) (29) (30) (31) (32) (33) (34) (35) (36) (37) (38) (39) (40) (41) (42) (43) (44)

PESTICIDE CHEMISTRY IN THE 20TH CENTURY Ross, R.D., Thesis, Univ. of C a l i f o r n i a , Davis, CA., 1974. Büchel, K.H., P e s t i c . S c i . 3, 89 (1973). Calderbank, Α., Adv. Pest Control Res. 8, 127 (1968). Fawcett, C.H., Taylor, H . F . , Wain, R.L., Wightman, F., Proc. Roy. Soc. (London), B148, 543 (1958). Tutass, H.O., Thesis, Univ. of C a l i f o r n i a , Davis, CA., 1967. Casida, J.E., Lykken, L., Ann. Rev. Plant P h y s i o l . 20, 607 (1969). Roth, W., Knüsli, Ε . , Experientia 17, 312 (1961). Hamilton, R.H., Moreland, D.E., Science 136, 373 (1962). Onley, J.H., Y i p , G . , Aldridge, M.H., J. Agr. Food Chem. 16, 426 (1968). Golab, T., Herberg, R.J., Parka, S.J., Tepe, J.B., J. Agr. Food Chem. 15, 638 (1967). Leitis, Ε . , Crosby, D.G., J. Agr. Food Chem. 22, 842 (1974). Alston, R.E., Turner, B.L., "Biochemical Systematics", P r e n t i c e - H a l l , Englewood Cliffs, N.J., 1963. L u c k w i l l , L.C., Lloyd-Jones, C.P., Ann. Appl. B i o l . 48, 613 (1960). Bailey, J.B., Swift, J.E., "Pesticide Information and Safety Manual", Univ. of Calif., Berkeley, 1968. Risebrough, R.W., Huggett, R.J., G r i f f i n , J.J., Goldberg, E. D., Science 159, 1233 (1968). Soderquist, C.J., Bowers, J.B., Crosby, D.G., J. Agr. Food Chem., submitted for publication (1976). PSAC, "Report on 2,4,5-T," OST, Exec. Office of the P r e s i ­ dent, Washington, D.C. 1971. Crosby, D.G., Wong, A.S., Plimmer, J.R. Woolson, E.A., Science 173, 748 (1971). Crosby, D.G., Wong, A.S., Science, submitted for publication (1976). Aller, H . E . , Dewey, J.E., J. Econ. Entomol. 54, 508 (1961). Dawson, J.H., Weed S c i . 17, 295 (1969). Kaufman, D.D., Kearney, P.C., Von Endt, D.W., Miller, D.E., J. Agr. Food Chem. 18, 513 (1970). Vlitos, A.J., Contr. Boyce Thompson Inst. 17, 127 (1953). Warner, H.L., Leopold, A.C., Plant Physiol. 44, 156 (1959). Turner, N.J., Corden, M.E., Phytopathol. 53, 1388 (1963). Foy, C.L., Bingham, S.W., Residue Rev. 29, 105 (1969). Crosby, D.C., Wong, A.S., J. Agr. Food Chem. 21, 1052 (1973). E. Bourcart, "Insecticides, Fungicides, and Weedkillers", Scott, Greenwood, and Son, London, 1913. U.S. Environmental Protection Agency, "Guidelines for Regis­ tering Pesticides i n the United States," Federal Register 40(123), 26802 (1975).

7 Fungicides—Past, Present, and Future JAMES G. HORSFALL

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The Connecticut Agricultural Experiment Station, Box 1106, New Haven, Conn. 06504

The year 1976 i s surely the year for celebration, f i r s t the b i c e n t e n n i a l of the Nation, then the centennial of the American Chemical Society (ACS). In t h i s context it i s p e r t i n e n t to examine the past, present, and future of the chemicals that are c a l l e d f u n g i c i d e s , the compounds widely used to protect the food of the world from p l a n t disease. I s h a l l l i m i t my remarks to fungicides for food, not for f i b e r . Why Use Fungicides On Food Crops? A b a s i c p r i n c i p l e i n p l a n t pathology i s that fungicides are used for crops that lack n a t u r a l r e s i s t a n c e to the fungus i n v o l v e d . Two notorious examples are Phytophthora infestans on potato and Venturia inaequalis on apple. No farmer would go to the labor and expense to spray h i s potatoes or h i s apples if he could have plants that s u c c e s s f u l l y fight off their fungi. This p r i n c i p l e says f u r t h e r that the amount of fungicide needed or the frequency of a p p l i c a t i o n i s i n v e r s e l y p r o p o r t i o n a l to n a t u r a l resistance. If n a t u r a l resistance i n the host breaks down, farmers often turn to f u n g i c i d e s . A classic example i s the breakdown i n 1970 i n the U . S . of r e s i s t a n c e of maize to Helminthosporium maydis. Farmers turned to zineb i n 1970 even thougn it i s expensive. Had not resistance been r e s t o r e d , zineb might w e l l be widely used on maize by 1976. Wheat i s a curious case. Resistance to the rust disease p e r i o d i c a l l y breaks down i n wheat. As soon as the search discovers a new gene for r e s i s tance i n wheat, a new race of the r u s t fungus appears. This i s the c l a s s i c case of the gene-for113

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gene h y p o t h e s i s . Despite t h i s p e r i o d i c c o l l a p s e of r e s i s t a n c e i n wheat, no f u n g i c i d e s a r e used i n r e a l l y s i g n i f i c a n t amounts. T h i s i s due t o t h e low cost/benefit ratio. Wheat r e t u r n s such a r e l a t i v e l y low v a l u e p e r h e c t a r e t h a t i t cannot c a r r y the c o s t of an e x p e n s i v e c h e m i c a l c o n t r o l regime. This i s e s p e c i a l l y t r u e s i n c e s o c i e t y , n o t t h e farmer, now b e a r s t h e c o s t o f t h e r e s e a r c h t o produce new v a r i e t i e s , n o t the c o s t o f c h e m i c a l treatment. R i c e i n Japan i s a s p e c i a l case f o r c e r e a l s t h a t n o r m a l l y a r e n o t sprayed w i t h f u n g i c i d e s . The r i c e p r i c e i n Japan i s m a i n t a i n e d h i g h by the government and, hence, farmers can a f f o r d t o spray and a i l o r almost a l l do s p r a y (Ou, 1 ) . F u n g i c i d e s Of The Past In 1776 when t h e N a t i o n was born, we had two u s e f u l f u n g i c i d e s f o r food c r o p s , e l e m e n t a l s u l f u r and copper s u l f a t e . D u r i n g the c e n t u r y b e f o r e t h e f o u n d i n g o f ACS, we added o n l y one more, l i m e - s u l f u r i n 1803 and t h i s was o n l y a v a r i a n t o f e l e m e n t a l sulfur. S i x y e a r s a f t e r ACS was founded, Bordeaux mixture was b o r n o f one o f those a c c i d e n t s that P a s t e u r s a i d happens t o t h e p r e p a r e d mind. In 1876 the y e a r t h a t ACS was founded, t h e F r e n c h wine growers i n a d v e r t e n t l y imported on American r o o t s t o c k s , a new d i s e a s e f o r them, downy mildew. They had been p r o t e c t i n g t h e i r grapes from p i l f e r a g e a l o n g t h e r o a d s i d e s w i t h a horrendousl o o k i n g s l u r r y o f copper s u l f a t e and h y d r a t e d l i m e . P r o f e s s o r A l e x i s M i l l a r d e t , h a v i n g the needed p r e p a r e d mind, was w a l k i n g down a road i n Bordeaux P r o v i n c e d u r i n g t h e h a r v e s t season o f 1882. He n o t i c e d t h a t the t r e a t e d grapes were f r e e o f downy mildew w h i l e the o t h e r s f a r t h e r back from t h e r o a d were i n f e c t e d . And thus was b o r n t h e m a t e r i a l t h a t became t h e h o l y water o f p l a n t p a t h o l o g i s t s who, f o r s i x t y y e a r s o r more, a n n o i n t e d t h e i r c r o p s w i t h i t u n t i l i t was l a r g e l y r e p l a c e d by o r g a n i c s . In 1888 formaldehyde, t h e f i r s t s y n t h e t i c f u n g i c i d e appeared. U n l e s s you count c h l o r o p h e n o l mercury i n 1913, l i t t l e r e a l l y new happened u n t i l 1934 when T i s d a l e and W i l l i a m s o f DuPont r e v e a l e d the d i a l k y l d i t h i o c a r b a m a t e s . They were e x p e n s i v e to make, however, and i t was d e p r e s s i o n days, and so DuPont was s k i t t i s h about t r y i n g t o s e l l them t o farmers when copper s u l f a t e c o u l d be bought f o r 6 c e n t s a pound. The p r i c e b a r r i e r was breached, however, when ;

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H o r s f a l l (2) i n t r o d u c e d c h l o r a n i l f o r legume seed treatment i n the l a t e t h i r t i e s . I t s o l d f o r about $1.50 p e r pound. In 1943 Dimond e t a l (3) i n t r o d u c e d the e t h y l e n e b i s d i t h i o c a r b a m a t e s . "These have gone on to dominate the f u n g i c i d e market f o r a g r i c u l t u r a l crops. In 1943, 2,3-dichloro-l,4-naphthoquinone appeared; i n 1947, 2-her>tadecyl-2-imidazoline; i n 1949, 6 - ( l - m e t h y l h e p t y l ) - 2 , 4 - d i n i t r o p h e n y l c r o t o n a t e ; i n 1952, N - t r i c h l o r o m e t h y l t h i o - 4 - c y c l o h e x e n e - l , 2 - d i c a r boximide ( c a p t a n ) .

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F u n g i c i d e s Of The

Present

Perhaps, we can b e g i n the p r e s e n t w i t h c a p t a n i n 1952. That g i v e s us a q u a r t e r o f a c e n t u r y . The development o f new compounds exploded i n the fift i e s , as d i d i n s e c t i c i d e s , and n e m a t i c i d e s . The F o r t y F u n g i c i d e s Of The World. By now the w o r l d uses about f o r t y f u n g i c i d e s on i t s c r o p s . The number depends on whether you count the m i x t u r e s and on how you count the v a r i a n t s - say o f the dithiocarbamates. The b e s t l i s t i n g o f f u n g i c i d e s t h a t we know o f i s p u b l i s h e d a n n u a l l y by the M e i s t e r P u b l i s h i n g Company of W i l l o u g h b y , Ohio i n t h e i r Farm Chemicals Handbook. They l i s t the f o l l o w i n g compounds o r types o f compounds as o f f i c i a l l y " r e g i s t e r e d " f o r use on p l a n t s i n the U n i t e d S t a t e s : a l l y l a l c o h o l , ammonium i s o b u t y r a t e , a n t i b i o t i c s , b e n z i m i d a z o l e t y p e s , c a r b o f u r a n , cadmiums, c a p t a n t y p e s , coppers, c a r b o x i n , d e h y d r o a c e t i c a c i d , Dexon (sodium [ 4 - ( d i methylamino) phenyl) diazo sulfonate), diphenyl, dodine, Dyrene ( a n i l a z i n e ) , formaldehyde, g l y o d i n , h a l o g e n a t e d h y d r o c a r b o n s , h y p o c h l o r i t e , Karathane (dinocap t y p e s ) , mercuries, mineral o i l s , n i t r o phenols, organic t i n s , organic a c i d s , pentachloronitrobenzene types, phenols, p y r i m i d i n e s , propylene o x i d e , p y r i d i n e s , p i p e r i d i n e s , q u a t e r n a r y ammoniums, q u i n o l i n o l s , quinones, s u l f u r s , and T e r r a z o l e (5ethoxy-3-trichloromethyl-l,2,4-thiadiazole). The M a j o r Crops Of The World. Mangelsdorf has s a i d t h a t s i n c e the dawn o f h i s t o r y man has used about 3000 s p e c i e s o f p l a n t s f o r food. Perhaps 150 o f these a r e i n w o r l d commerce today, but o n l y 10 p e r c e n t o f these r e a l l y f e e d the p e o p l e o f the world. M a n g e l s d o r f s 15 s p e c i e s i n c l u d e f i v e cer e a l s ; r i c e (Oryza s a t i v a ) , wheat ( T r i t i c u m s p p . ) , maize (Zea mays), sorghum (Sorghum c e r e a l e ) , and n

1

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b a r l e y (Hordeum v u l g a r e ) ; two sugar p l a n t s : sugar cane (Saccharum o f f i c i n a r u m ) and sugar b e e t ( B e t a vulgaris): three root crops: p o t a t o (Solanum tuberosum), sweet p o t a t o (Ipomea b a t a t a s ) , and c a s s a v a (Manihot e s c u l e n t a ) ; t h r e e legumes: common bean ( P h a s e o l u s v u l g a r i s ) , soybean ( G l y c i n e max), and peanut ( A r a c h i s Jiypogaea); and two t r e e c r o p s : coconut (Cocos n u c i f e r a ) and banana (Musa s p p . ) . In d i s c u s s i n g f u n g i c i d e s we must add some non-food c r o p s ; r u b b e r (Hevea b r a s i l i e n s i s ) , c o f f e e ( C o f f e a spp.), c o t t o n (Uossypium spp.), t e a and tobacco ( N i c o t i a n a tabacum). The M a j o r D i s e a s e s Of The Crops Of The World. The major d i s e a s e s o f r i c e a r e b l a s t and b a c t e r i a l b l i g h t ; wheat, r u s t s and smuts; maize, stem and r o o t r o t s ; b a r l e y , h e l m i n t h o s p o r i a l l e a f spot and r o o t r o t s ; sugar cane, v i r u s e s ; sugar b e e t , v i r u s e s and c e r c o s p o r a l l e a f spot; p o t a t o , l a t e b l i g h t and v i r u s e s ; sweet p o t a t o , stem r o t ; c a s s a v a , mosaic; common bean, v i r u s e s , b a c t e r i a l b l i g h t s , and r o o t r o t s ; soybean, r o o t r o t ; peanut, l e a f spots and r o o t r o t ; coconut, p r a c t i c a l l y none; banana, w i l t and S i g o t o k a ; rubber, l e a f b l i g h t ; c o f f e e , r u s t ; c o t t o n , w i l t and r o t s o f s e e d l i n g s and b o l l s ; t o b a c c o , b l u e mold; t e a , b l i s t e r b l i g h t . The massive tonnages o f f u n g i c i d e s used i n the w o r l d a r e a p p l i e d t o f o l i a g e d i s e a s e s o f the c r o p s w i t h h i g h v a l u e p e r a c r e - banana, p o t a t o , a p p l e , c i t r u s , v e g e t a b l e s , t o b a c c o , peanut, c o f f e e , t e a , rubber. Few f u n g i c i d e s go on the f o l i a g e o f t h e c e r e a l s (except r i c e i n J a p a n ) , legumes, and c o t t o n . The r o o t c r o p s g e n e r a l l y remain a l o o f from f u n g i c i d a l treatment. Yes, t h e w o r l d t r e a t s seeds f o r damping o f f , and t r e a t s s o i l i n seedbeds and greenhouses f o r r o o t r o t , b u t seldom i n t h e f i e l d . There i s some s p r a y i n g o f c o t t o n seed as i t i s planted. The w o r l d uses some f u n g i c i d e s f o r seed borne d i s e a s e s l i k e t h e c e r e a l smuts and i t uses some f u n g i c i d e s t o p r e v e n t decay o f f r u i t s and v e g e t a b l e s enroute t o market. The tonnage i s s m a l l , however. D e s p i t e t h e g r e a t a r r a y o f f o r t y f u n g i c i d e s , one i s d e p r e s s e d t o see how many o f the w o r l d s major plant diseases are s t i l l not properly c o n t r o l l e d b a c t e r i a l d i s e a s e s , v i r a l d i s e a s e s , r o o t r o t s , and wilts. The c h a l l e n g e beckons. Chemotherapy i s one p o s s i b l e answer t o t h e challenge. T r e a t the p l a n t from the i n s i d e and n o t

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on t h e o u t s i d e o n l y as i n t h e p a s t . c a l l t h i s "inneretherapy".

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The D r i v e F o r Chemotherapy. Chemotherapy o f p l a n t d i s e a s e has advanced r a p i d l y i n r e c e n t y e a r s f o l l o w i n g a slow s t a r t i n t h e ' f o r t i e s . I t has gone so f a r t h a t we now have a whole book ( 5 ) d e v o t e d t o i t and a r e v i s i o n underway a f t e r o n l y t h r e e y e a r s . Perhaps t h e f r o n t - r u n n i n g chemotherapeutant i s benomyl and i t s b e n z i m i d a z o l e r e l a t i v e s which have a c h i e v e d d r a m a t i c r e s u l t s on v a s c u l a r d i s e a s e s . Other s e l e c t i v e t h e r a p e u t a n t s a r e c a r b o x i n , s e v e r a l p y r i m i d i n e s , t r i f o r i n e , s e v e r a l m o r p h o l i n e s , 6a z a u r a c i l , a z e p i n e s , p h e n y l t h i o u r e a s , c h l o r o n e b , and others. L i k e any new f i e l d , chemotherapy o f p l a n t d i sease has i t s semantic problems. When we h e l p e d i n i t i a t e i t i n 1940, we c a l l e d i t chemotherapy i n l i n e with our medical c o n f r e r e s . Literally i t means, o f c o u r s e , c h e m i c a l c u r e , b u t i t i s g i v e n a c o n n o t a t i o n o f i n t e r n a l t h e r a p y as w e l l . There i s a s t r o n g tendency, p a r t i c u l a r l y i n B r i t a i n t o l a b e l i t s y s t e m i c f u n g i c i d e . " The semantic p r o b l e m h e r e i s t h a t n o t a l l chemotherapeutants a r e s y s t e m i c fungicides. Even benomyl, t h e l e a d i n g c o n t e n d e r , i s not a t r u e f u n g i c i d e . It i s a fungistat. Chemotherapy o f p l a n t d i s e a s e has a b u i l t - i n weakness, n o t c o n f r o n t i n g t h a t o f a n i m a l t h e r a p y . P l a n t s have no phagocytes t o c l e a n up t h e s t r a g g l e r s t h a t a r e m i s s e d by the t h e r a p e u t a n t . Penicillin i s only b a c t e r i o s t a t i c . I t does n o t k i l l t h e b a c t e r i a but i t keeps them few enough f o r l o n g enough t o g i v e t h e phagocytes a chance. Benomyl does n o t enjoy the b e n e f i t of phagocytes. I t has a p a r t i a l l y compensating advantage, however. I t i s not excreted by the k i d n e y s and i t t h e r e f o r e l a s t s l o n g e r i n t h e plant. A l e s s s t a b l e compound would be l e s s e f f e c tive. n

The Rachel Carson Syndrome. In June 1962 i n the m i d d l e o f one o f the w o r l d ' s g r e a t c i t i e s and f a r from t h e farm, t h e r e appeared i n one o f t h e w o r l d ' s s o p h i s t i c a t e d j o u r n a l s (The New Y o r k e r ) , an a r t i c l e t h a t s e t t h e a g r i c u l t u r a l segment o f t h e w o r l d on f i r e . I t was w r i t t e n by a l a d y m i s s i o n a r y named Rachel Carson. L a t e r i n 1962 i t was expanded i n t o a book, S i l e n t S p r i n g ( 6 ) . She s a i d t h a t t h e w o r l d was s u f f o c a t i n g i n a p o i s o n o u s r a i n o f p e s t i c i d e s and she accused t h e farmers o f p o i s o n i n g h e r food. The s c a r e she s e t i n motion has spread around

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the g l o b e . teeth.

C o n s t r a i n t s have sprung up

THE

like

20TH

CENTURY

dragons'

The Rapid R i s e In C o n s t r a i n t s . Her book changed most o f the r u l e s o f the game i n d e v e l o p i n g and u s i n g f u n g i c i d e s . For i n s t a n c e , c h l o r a n i l (Spergon; was f i r s t t e s t e d on spores i n the l a b o r a t o r y i n 1938 ( 2 ) . By A p r i l 1940, farmers o f New York S t a t e were u s i n g i t by the hundred weight and by 1941 by the t o n to t r e a t pea and l i m a bean seed to p r o t e c t a g a i n s t seed decay. That was two y e a r s from l a b o r a t o r y to f i e l d . And now i t takes s i x o r seven y e a r s to go the same d i s t a n c e . In the meantime uncounted numbers o f r a t s and mice, even dogs, must be s a c r i f i c e d on the C a r s o n a l t a r . When lawy e r s and c o n t r o l o f f i c i a l s by the s c o r e get i n t o the a c t , d e v e l o p m e n t a l c o s t s shoot sky h i g h and the end i s by no means i n s i g h t . The c o n s t r a i n t s have i n c r e a s e d the h a z a r d s o f f a r m i n g because d i s e a s e s a r e now more d i f f i c u l t to control. Carson's book has spawned a h o s t o f "new e c o l o g i s t s ' who e n j o y b a i t i n g farmers by s a y i n g t h a t they p o l l u t e the environment and the food o f man. Farmers a r e f i g h t i n g back. A bumper s t i c k e r on a farmer's t r u c k now r e a d s , " I f you c r i t i c i z e a g r i c u l t u r e , don't t a l k w i t h y o u r mouth f u l l . " The mouths of the new e c o l o g i s t s are a l l f u l l . D e s p i t e a l l the a l l e g e d p o i s o n s i n the food, stomach c a n c e r i s d e c l i n i n g ; sons and daughters a r e growing t a l l e r than t h e i r p a r e n t s ; and a t h l e t e s c o n t i n u a l l y break world's r e c o r d s . The DDT i n the f a t o f the a t h l e t e s must be r e s p o n s i b l e f o r the new records ! ! The Carson syndrome has had important impacts on the s c i e n t i f i c base o f f u n g i c i d e s . For example, a study o f the membership l i s t s o f the American P h y t o p a t h o l o g i c a l S o c i e t y shows t h a t the number o f p l a n t p a t h o l o g i s t s who work w i t h f u n g i c i d e s i s falling. 1

The S e a r c h For S e l e c t i v i t y . I had the honor o f s e r v i n g on a committee a p p o i n t e d a t the r e q u e s t o f P r e s i d e n t John F. Kennedy to examine the s i g n i f i cance of Carson's book. Our r e p o r t t o him i n the s p r i n g o f 1963 was e n t i t l e d "The Use o f P e s t i c i d e s " (7). Among o t h e r t h i n g s , we recommended t h a t p e s t i c i d e s , i n c l u d i n g f u n g i c i d e s , be made more s e l e c t i v e . And they were. B i a s t i n (pentachlorobenzyl alcohol) i s select i v e f o r r i c e b l a s t , Dexon (sodium [ 4 - ( d i -

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methylamino) phenyl] • d i a z o s u l f o n a t e ) f o r Pythium, p e n t a c h l o r o n i t r o b e n z e n e f o r R h i z o c t o n i a , and c a r boxin f o r Basidiomycetes. S e l e c t i v i t y i s b r i l l i a n t l y d i s p l a y e d by a m u l t i p l i c i t y o f compounds developed f o r the c o n t r o l of powdery mildews. For 148 y e a r s from 1803 u n t i l 1951 s u l f u r was the o n l y s i g n i f i c a n t f u n g i c i d e f o r powdery mildew. In 1949' a new f u n g i c i d e appeared w i t h the p u b l i c a t i o n of 6 - ( l - m e t h y l h e p t y l ) - 2 , 4 d i n i t r o - p h e n y l c r o t o n a t e ( 8 ) . Two y e a r s l a t e r Yarwood r e p o r t e d (9) i t s anti-powdery mildew p r o p e r ties. I t went on to worldwide usage and thus stimulated a vast search f o r others. Now we have many e f f e c t i v e compounds, i n c l u d i n g benomyl, b i n a p a c r y l , dodemorph, f o l p e t , p a r i n o l , p i p e r a l i n , pyrazophos, t h i o p h a n a t e , t r i d e m o r p h , t r i f o r i n e , and o t h e r s . The R i s e Of Fungus R e s i s t a n c e . The d r i v e f o r s e l e c t i v i t y t h a t i s urged on by the Carson p r e s s u r e has exaggerated a s m a l l t r e n d t h a t had a l r e a d y shown up b e f o r e Carson. Fungi had developed r e s i s t a n c e t o some of the s e l e c t i v e f u n g i c i d e s . When H o r s f a l l p u b l i s h e d (2) h i s second book s i x y e a r s ahead o f Carson, he had d i f f i c u l t y i d e n t i f y i n g any r e s i s t a n t fungi. A few were noted, but w i t h i n f i v e v e a r s a f t e r Carson, Georgopoulos and Z a r c o v i t i s demonstrated d r a m a t i c a l l y that s e l e c t i v i t y i s a t r i c k y s o l u t i o n to a v e r y d i f f i c u l t problem posed so nonchalantly The b i o l o g y i s f a i r l y s i m p l e . The more s e l e c t i v e we make our f u n g i c i d e s , the fewer the b l o c k s i n the p a t h of the fungus, and the e a s i e r i t can f i n d a bypass around the b l o c k . However p r o m i s i n g a compound may be as an o r i g i n a l k i l l e r o f the p e s t fungus, i t s use may be eroded by r e s i s t a n c e almost by the time i t i s a b l e to pass through a l l the maze of o f f i c i a l approval. The r a p i d b i o l o g i c a l e r o s i o n of new compounds i s v e r y d i s c o u r a g i n g to those who must develop them to c o n t r o l p l a n t d i s e a s e . F u n g i c i d e s F o r The

Future

We a l l want answers to the q u e s t i o n , where n e x t ? Where does f u n g i c i d e r e s e a r c h go now? I agree w i t h the D a n i s h h u m o r i s t , V i c t o r Borge, who has s a i d , " F o r e c a s t i n g i s a d i f f i c u l t b u s i n e s s , esp e c i a l l y f o r the f u t u r e " . S t i l l , we must l o o k ahead. The T a c t i c s And S t r a t e g y Of D i s c o v e r y . By and

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l a r g e the world's f u n g i c i d e s have come from the i n d u s t r i a l c o u n t r i e s o f U.S.A., B r i t a i n , S w i t z e r l a n d , German and Japan. I t seems r e a s o n a b l e t o say t h a t the development o f new f u n g i c i d e s by i n d u s t r y i s becoming an i n c r e a s i n g l y more d i f f i c u l t b u s i n e s s . There are a t l e a s t t h r e e reasons f o r t h i s . (1) The r e g u l a t o r s are i n t r o d u c i n g an e v e r i n c r e a s i n g number o f t e s t s t h a t must be done o v e r an e v e r - i n c r e a s i n g number o f y e a r s and o v e r an e v e r i n c r e a s i n g number o f t e s t organisms. This dimini s h e s the l i k e l i h o o d o f f i n d i n g a u s e f u l compound and m u l t i p l i e s the c o s t . As a r e s u l t the s m a l l e r l e s s w e l l c a p i t a l i z e d companies are d e s e r t i n g the f i e l d and t h o s e t h a t remain seem to be spending a l a r g e r p r o p o r t i o n o f t h e i r time d e f e n d i n g the compounds they have a l r e a d y marketed o r a r e h o p i n g to market, and p r o p o r t i o n a l l y l e s s time on e x p l o r i n g . (2) S i n c e enormous numbers o f compounds have a l r e a d y been made and s c r e e n e d , the odds o f f i n d i n g a new one seem to be d i m i n i s h i n g (von Rumker e t a l , 11). (3) The c o m p e t i t i o n f o r o l d markets i s keen and new markets seem t o d e v e l o p s l o w l y . Some w i l l say, " L e t the p u b l i c s e c t o r of s o c i e t y take o v e r the j o b . " T h i s won't s o l v e the c o s t problems o f r e g u l a t i o n o r the p r o b a b i l i t y of f i n d i n g new and u s e f u l s t r u c t u r e s , and b e s i d e s , s o c i e t y does not do w e l l i n the m a n u f a c t u r i n g b u s i n e s s . S o c i e t y may w e l l be f o r c e d , however, t o take o v e r the t e r r i b l e c o s t s o f s a f e t y determination. That we a r e s t i l l g r e a t l y c h a l l e n g e d i s w i t nessed by the l a r g e number o f u n c o n t r o l l e d f u n g a l d i s e a s e s , not to mention v i r a l and b a c t e r i a l d i seases. The r o o t r o t s , the v a s c u l a r w i l t s , and the c e r e a l r u s t s comprise the major c h a l l e n g e s . We p r o b a b l y w i l l f i n d the g r e a t e s t s u c c e s s by t e s t i n g c a n d i d a t e compounds on the p l a n t s themselves. This w i l l encourage s e l e c t i v i t y and thus runs a s e v e r e r i s k of developing r e s i s t a n c e .

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t

Cooperate With P l a n t B r e e d e r s . S u r e l y the odds run h e a v i l y a g a i n s t s u c c e s s i n f i n d i n g t h e r a p e u t a n t s t h a t can escape the r e s i s t a n c e problem, but p l a n t b r e e d e r s f a c e h a z a r d s as g r e a t . Perhaps, we s h o u l d j o i n hands w i t h the b r e e d e r s . Perhaps we c o u l d o u t w i t the fungus by combining a r e s i s t a n c e gene w i t h a chemotherapeutant. T h i s would m u l t i p l y the odds i n our f a v o r . Cooperate With P h y s i o l o g i s t s .

Another p o s s i -

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b i l i t y i s t o j o i n hands w i t h those who study t h e p h y s i o l o g y o f d i s e a s e . P l a n t s do have b i o c h e m i c a l and p h y s i c a l means f o r p r o t e c t i n g themselves from d i s e a s e a t t a c k . Here i s a p o t e n t p o s s i b i l i t y o f a s y n e r g i s t i c approach. S t i l l another p o s s i b i l i t y i s t o search f o r compounds t h a t a c t on t h e f e a t u r e s t h a t c h a r a c t e r i z e and d i s t i n g u i s h f u n g i from h i g h e r p l a n t s and humans. A n t i d i f f e r e n t i a t i o n Compounds. Fungi d i f f e r ent iaFêTli$îêrr~^ from t h e i r h o s t s and from humans. F o r example, f u n g i have w a l l s o f c h i t i n . They reproduce through s p o r e s . Humans and h i g h e r p l a n t s do n o t . Very few s c r e e n s have been d e l i b e r a t e l y developed t o e x p l o i t t h e s e differences. We have d i s c o v e r e d enough compounds a c c i d e n t a l l y t o be a b l e t o say t h a t p o s s i b i l i t i e s e x i s t , however. G r i s e o f u l v i n , f o r example, c u r l s and t w i s t s t h e germ tubes so t h a t they a r e u n a b l e to i n f e c t t h e t i s s u e . Polyoxin i n t e r f e r e s with c h i t i n s y n t h e s i s . B i a s t i n p r e v e n t s an a p p r e s s o r i u m of t h e r i c e pathogen from s e n d i n g down an i n f e c t i o n peg i n t o t h e l e a f , and so i t goes. In o u r l a b o r a t o r y we have developed a h i g h l y e f f e c t i v e and r a p i d s c r e e n t o p i c k o u t a n t i s p o r u l a n t s ( 1 2 ) . We c a n use the same t e c h n i q u e s f o r p i c k i n g o u t a n t i c o n i d i o p h o r e compounds ( 1 3 ) . Summary We- d i s c u s s t h e major c r o p s o f t h e w o r l d and t h e i r major d i s e a s e s and i n d i c a t e how d i s c o u r a g i n g l y few a r e those t h a t c a n now be a d e q u a t e l y c o n t r o l l e d by f u n g i c i d e s o r o t h e r w i s e . We l i s t t h e world's 40 f u n g i c i d a l t y p e s . The e n v i r o n m e n t a l i s t s a r e a d d i n g more and more c o n s t r a i n t s o f more and more c o m p l e x i t y on t h e p r o c e s s o f d e v e l o p i n g new compounds. They a r e i n s i s t i n g on s e l e c t i v i t y . This l e a d s i n t o fungus r e s i s t a n c e . T h i s lowers t h e odds of e v e n t u a l s u c c e s s and d i s c o u r a g e s t h e i n n o v a t o r s . We urge r e s e a r c h on s c r e e n i n g p r o c e d u r e s so t h a t they may be more d i r e c t l y aimed a t t h e f u n g a l l i f e p r o c e s s e s ( c h i t i n s y n t h e s i s , f o r example) t h a t a r e d i f f e r e n t from h o s t o r human rocesses. Literature 1.

Cited

Ou, S . H . "Rice D i s e a s e s . " 368 p p . wealth Mycol. Inst. Kew, S u r r e y , 1972.

CommonEngland.

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2. 3. 4. 5. 6.

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7. 8. 9. 10. 11. 12. 13.

CENTURY

H o r s f a l l , J.G. " P r i n c i p l e s of F u n g i c i d a l Action." 279 pp. Chronica Bot. Co. Waltham, Mass. 1956. Dimond, A.E., Heuberger, J.W., and H o r s f a l l , J.G. Phytopathol. 1943. 33:1005-1007. Mangelsdorf, P.C. Proc. Nat. Acad. S c i . U . S . A . 1966. 56: 370-375. Marsh, R.W. E d i t o r . "Systemic F u n g i c i d e s . " 321 pp. Halstead Press. New York. 1972. Carson, Rachel. " S i l e n t S p r i n g . " 368 pp. Houghton Mifflin Co. Boston, Mass. 1962. P r e s i d e n t ' s Science Advisory Committee. "The Use of P e s t i c i d e s . " The White House. Washington, D . C . 1963. R i c h , S. and H o r s f a l l , J.G. Phytopathol. 1949. 39:19. Yarwood, C.E. Proc. IInd Int. Congr. of Crop P r o t e c t i o n . 1951. p. 1-22. Georgopoulos, S . G . and Z a r a c o v i t i s , C. Ann. Rev. Phytopathol. 1967. 5: 109-130. Von Rumker, R., Guest, H . R . , and Upholt, W.M. Bioscience. 1970. 20: 1004-1007. Lukens, R.J. Phytopathol. 1960. 50: 867-868. Lukens, R.J. and H o r s f a l l , J.G. 1971. Phyto pathol. 1971. 61:13.

8 Metallo-Organic Fungicides G. J. M. VAN DER KERK

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch008

Der Rijksuniversiteit te Utrecht, Croesestraat 79, Utrecht, The Netherlands

Metals - or rather metal ions - are indispensable for the regulation of life processes and are thus essential for a l l forms of l i f e . In the first place metal ions play an important role as cationic components of the systems that regulate the osmotic phenomena within cells and tissues. Further, they can act as matrixes in the folding and unfolding of macromolecular cell components and thus influence the molecular shapes of such components, so important for their biological functioning. But more related to the subject occupying us today are the functions of metal ions as constituents of oxygen carriers and in particular of biocatalysts, such as co-enzymes and enzymes. In fact, a great number of metal ions, both of main group and of transition metals, are known to be of essential significance for the proper functioning of widely varying biocatalytic systems. I refer to the occurrence of iron, copper and vanadium in the oxygen-carrying systems in the blood of vertebrates, many invertebrates and tunicates, respectively. Further, to the presence of magnesium in the photosynthetic pigment chlorophyll, of zinc in the enzyme carbonic anhydrase, essential for an adequate respiratory exchange in mammals and birds, and in several other enzymes occurring both in higher and lower animal and plant species. Finally, to the necessity, for a great variety of life processes, of many transition metal ions frequently in very small amounts, which has led to the indication "essential trace metals". On the other hand, it is well known that many metal ions for which no physiological functions are apparent - e . g . those of silver, mercury, cadmium, thallium, lead and arsenic - are more or less toxic for a l l types of living organisms and that they exert inhibitory activity, sometimes in extremely 123

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low concentrations, toward enzymic reactions both in vivo and in vitro. When discussing "metallo-organic fungicides" , it is clear that one important aspect of this topic is to define the subject. Metals do not occur as such in life processes and this is even true for metal ions in a strict sense. Metal atoms and ions are very reactive electron-deficient centers which surround themselves by a l l kinds of electron-donating groups, molecules and ions. These surrounding groups are called ligands and modern organo-metal and metal-coordination chemistry studies the bonding interactions between metals (either atoms or ions) and ligands, as well as the structures and properties of organometallic and metal-coordination compounds. The arrangement of ligands around a metal center has important consequences. The chemical and physical properties of both the metal and the ligands are changed as a result of charge transfer. The number of ligands surrounding a metal center - the coordination number - and the nature of the metal center and of the ligands determine the geometry and the bond characteristics of coordination compounds. Ligands may be bound to the metallic center very loosely and for this reason be susceptible to exchange for other l i gands with higher affinity for the metal center. Also, metal ions may expel other metal ions from their coordination complexes because of better coordinating capacity. On the other hand, the bonding interaction between metal ions and ligands may be so strong that certain complexes are stable even in biological systems containing a variety of potential ligand molecules. This brief exposition just serves to impress upon you that the interaction of metal centers with ligands gives rise to metal-coordination structures with specific chemical and physical properties, which may result in similarly specific physiological effects. The traditional copper fungicides are in fact inorganic copper coordination compounds The still most important group of organic protectant fungicides, the dithiocarbamates, are applied in the form of their metal-coordination compounds. Dimethyldithiocarbamate as the iron complex ferbam and the zinc complex ziram, ethylenebisthiocarbamate as the zinc complex zineb and the manganese complex maneb.

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From our own work I cite two examples which just may serve to illustrate the importance of metal-ligand interactions in the functioning of dithiocarbamate fungicides. The first example originates from older work (1) on the mode of antifungal action of dimethyldithiocarbamates. It could be proven that fungitoxicity is not connected with the dimethyldithiocarbamate ion as such or with its iron or zinc complexes used in practice, but with the very special pro­ perties of its 1:1 copper complex which is formed from the very minute but ubiquitous amounts of copper present in all natural waters, even in "pure" tap water. In fact, this 1:1 complex C u D D C serves as a "copper carrier" , bringing it to the copper-susceptible intracellular system, which is the dithiol compound lipoic acid or the d i thiol system lipoic acid dehydrogenase:

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch008

+

S

S

Cut

χ$

S , -

c CH

x

CH

3

S

Cu DDC +

3

CH

3

c

, S

CH

3

DDC"

As a consequence, the antifungal action of the dimethyl­ dithiocarbamates is antagonized by all ligand molecules which can effectively compete with the cellular dithiolsystem for the 1:1 complex C u D D C . One very effective antagonist is the generally occurring amino acid histidine. But, to our surprise, the most effective antagonist appeared to be a high­ er homologue of the dimethyldithiocarbamate ion, v i z . the dibutyldithiocarbamate ion, which itself or in the form of its metal-coordination compounds is completely inactive as a fungicide. Of course, this observation could be rationalized: it depends on the complex stabilities and the solubility pro­ perties of the 1:1 and the 1:2 copper/dialkyldithiocarbamate complexes which are different for the methyl and butyl deriva­ tives . +

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The second example demonstrates impressively the influence of coordinating metals on the chemical properties of ligands (2). Aromatic dithiocarbamate derivatives of the type:

NH-C-S-CH COONa II

2

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch008

are stable at pH 4-7 and are not fungitoxic within this pH range. Upon adding a zinc salt to such a compound at low pH an insoluble stable zinc coordination complex is formed:

/

V

\=/

zn

S

0 ^

X

S

C-NH-
y~~X

Upon suspending this complex in water or a nutrient medium and bringing the pH value to about 7, the following reaction occurs spontaneously: S-CH -C^ 2

X-^-NH-C^ ~ \

.

^°"^lY "O X

Zn- - -

\

rNCS + Z

S-CH COO2

+

H

2°

An aromatic isothiocyanate is formed which, depending on the nature of the substituent X, may be moderately to highly fungitoxic. I will not discuss the mechanism of this reaction but just want to emphasize the change in chemical behaviour resulting from complex formation. Fungi require iron, copper, zinc and a few other metals for proper growth and development, but zinc and in particular copper ions, when supplied in more than optimal amounts, are notorious as well for their fungicidal effects. On the other hand, a number of metal ions for which no physiological functions are known, such as the ions of silver, mercury, cadmium, nickel and lead, may exert powerful fungicidal activity.

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Still another category is represented by the orqanometallic compounds, i . e . , metal compounds in which at least one direct metal-carbon bond occurs. The great majority of these types cf compounds are real artifacts since living systems are very restricted in their capability to establish such bonds. The one exception is the capacity of some micro-organisms to methylate certain metals, e . g . arsenic, antimony and mercury, probably as a kind of detoxification mechanism. Methylcobalamin is the only organometallic compound known to have a physiological function in life processes. It has been observed that quite generally the toxic effects of organometallic compounds are stronger than those of the underlying metal ions. This is particularly true for the antimicrobial effects. The metal tin shows this phenomenon in a rather dramatic way. Whereas scarcely any pronounced biological effect is known for tin, either in the stannous or the stannic form, certain trialkyltin compounds belong to the most active fungicides known at present. One reason for the enhanced activity of organometallics in comparison to the corresponding inorganic forms may be the generally higher lipid solubility of the former. It is certainly true that owing to this property, organometallics can reach places that are inaccessible to metal ions. It has been found, however, that frequently profound differences exist between the mode of action of organic and inorganic metal compounds. Moreover, of many multivalent metals, different types of organometallic compounds exist, depending on the number of available valencies that are occupied by a carbon atom of an organic group. The most "organic" types in general are not necessarily the most active ones. Moreover, the biochemical mode of action of the several types may be different for one and the same metal. Whatever explanations will be found, it is very clear that bringing a metal to the organic form is likely to change its chemical properties and its physiological effects very profoundly. Of course, this has been known for a long time for mercury and arsenic. But in particular the study of organotin compounds has led to the insight that organylation of metals not only modifies existing chemical and physiological properties but rather introduces the conditions for completely new ones. Keeping in mind that the periodic system contains about 75 elements that are generally considered to be metals, it

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would seem that a tremendous field of exploration still lies ahead of u s . This is certainly true but it should be realized that there are a number of important limiting factors. The first limitation is related to the chemical properties of metal-carbon bonds. All main group, and first and second subgroup metals form "normal" two-electron metal-carbon bonds which vary from strongly polar (ionic) to rather covalent. All of the strongly polar and many of the covalent metal-carbon bonds are chemically very reactive and, in particular, are sensitive toward water and/or oxygen. This eliminates all the metals occurring in the first three groups of the periodic system with the exception of mercury. In fact, only the fourth main-group metals silicon, germanium, tin and lead, and the fifth main-group metals arsenic, antimony, and bismuth are left. A l l remaining electropositive elements, known as the transition metals, are able to form organometallic derivatives but these are of a very peculiar nature. In bond formation leading to metal-carbon bond relations coordination numbers that are higher than the usual valencies are involved. The study of this class of organometallic compounds is rather new and is still in progress. Both stable and unstable representatives are known. So far no clear picture exists regarding the physiological properties of the chemically stable organo-transition metal compounds. With a view to the great range of transition metals and to their widely varying capacity for bond formation, a systematic study of the physiological properties of the organo-transition metal compounds seems very attractive. It should be recalled that several transition metals play a decisive role in normal cell metabolism. Further, it is known that a group of compounds belonging to this c l a s s , the metal carbonyls, are extremely toxic toward mammals. On the other hand, there are indications that our expectations must not be set too high. A great variety of chemically extraordinary interesting transition metal organometallics has been prepared during the past decades. I think in particular of the types known as "sandwich compounds", exemplified by ferrocene, bisbenzenechromium, bis?7-allyl nickel and cyclobutadienemetal complexes:

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biscyclopentadienyliron "ferrocene"

Fungicides

<

129

c if

bisbenzenechromium

M

bis (ÎÎ - a l l y 1) nickel

X

cyclobutadienemetal complexes

Using direct or indirect methods, an astonishing number and variety of functionally-substituted structural variants of these types of compoundshave been prepared and investigated. So far, the search for variants with interesting physiological properties in the widest sense has been pretty much in vain. A further limitation has been the difficulty of introducing functional groups into organometallic compounds of the main group metals. Until quite recently, organometallic chemistry was simple insofar, that organic groups bound to such metals were mostly unsubstituted hydrocarbon radicals, both aliphatic and aromatic. This restriction depended on the special methods required for establishing metal-carbon sigma bonds which were not very ' suitable for the introduction of radicals containing functional groups such as hydroxyl, amino, carboxyl, etc. It is well known that in organic chemistry proper the presence of different and of differently placed functional groups is one of the very bases for the widely divergent physiological properties of organic molecules. In recent years considerable progress has been made in the synthesis of metal-carbon bonds and methods have become available for the preparation of widely divergent types of functionally substituted organometal-

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PESTICIDE C H E M I S T R Y IN T H E 2 0 T H C E N T U R Y

lie compounds. There is no doubt but that these developments will lead to a renewed interest into the biological implications of a thus widened organometallic chemistry. Nevertheless, there are again reasons not to be too optimistic in this respect. For the transition metals this has already been indicated. For the main group metals, in particular for tin, a truly functional organometallic chemistry has been developed by Noltes and van der Kerk (1958), but thus far the introduction of functional groups into fungitoxic organotin compounds has had the effect of abolishing activity rather than modifying it. A few examples will be given later on. In the following, I shall review the antimicrobial and in particular the antifungal activity of organometallic compounds. After some consideration, I have decided not to discuss the organomercurials. At first sight, this may seem unjustified. The historical significance of a great variety of organomercury compounds as agricultural fungicides and as general purpose biocides in the prevention of biodeterioration has been phenomenal. But everywhere a strong tendency exists to banish the use of organomercurials because of the very serious environmental health hazards involved in their applications. There is no doubt that their use will be forbidden altogether. But let us not forget that in the past very modest amounts of organomercurials have been extremely effective in the combat or rather the prevention, of economically very important plant diseases of cereals. And further, that no really satisfactory substitutes have been developed so far. Whereas the indiscriminate use of organomercurials is no longer justified, it remains to be seen whether their total abolishment may be considered a wise decision. However this may be, for the time being the organomercurials are a part of history and not of the present. In connection with what I have said before, this leaves me with the organometallic derivatives of the fourth and fifth main-group metals: silicon, germanium, tin, lead, arsenic, antimony and bismuth. A further restriction i s , that the fourth group metal lead and the fifth group metal arsenic are highly toxic in their inorganic forms and that the applications of their organic forms pose lasting environmental problems. On the basis of practical considerations my d i s cussion will therefore be restricted to the fourth group elements silicon, germanium and tin, some data for lead being nevertheless included, and with the fifth group elements antimony and bismuth.

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Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch008

Antimicrobial, in Particular Antifungal, Activity of Organometallic Compounds of Silicon, Germanium, Tin and Lead. Among the fourth-main group elements,carbon, silicon, germanium, tin and lead, carbon is so to say the "element of life" . It is worthy of note that silicon is the only other fourth group element known to be utilized by living organisms. Many monocotyledonous plants and lower animals and plants, e . g . radiolaria and diatoms, use silica for building up their structural elements. It is not known with certainty whether the solubilization, transportation and deposition of silica is a truly physicochemical process or whether enzymic processes are involved as w e l l . It would be tempting to deal here with the remarkable results published during the past ten years or so by Voronkov and his group [3] in the USSR on the broad range of physiological effects shown by a great variety of organosilicon coordination compounds. This is beyond the scope of my paper, but one compound will be mentioned later o n . Apart from the observations of Voronkov, organosilicon compounds had never exhibited any significant physiological activity. The antimicrobial, in particular the fungicidal and bactericidal effects of organogermanium, -tin and -lead compounds were discovered in Utrecht and have been extensively studied by our group _[4}. The stable fourth main group organometallic compounds all contain the metal in the oxidation state four. Since most of the relevant compounds contain only one metal atom per molecule the following basic types of compounds must be d i s tinguished: R M 4

Type

I

R MX 3

II

R

2

M X

III

2

R M X

3

IV

R represents a group attached to the metal atom by means of a carbon atom. It is generally a hydrocarbon (alkyl, aralkyl, or aryl) group. In one and the same compound the groups R may be equal (symmetrical compounds) or different (unsymmetrical compounds). In the special case in which one or more R groups contain a functional substituent they are called functionally substituted compounds. X denotes a group not linked to the metal atom via carbon. It may stand for a halogen, hydroxyl, oxygen, alkoxyl, sulfur, or an organic or inorganic acid radical.

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In these compounds the physical and chemical stability of the metalcarbon bonds decreases from silicon to lead, but all compounds may be considered stable to fairly stable under "physiological" conditions. The anionic groups X are less firmly bound and can be exchanged rather easily. Our work started in 1950 with tin and was later extended to germanium and lead. For the series of ethyltin compounds Luijten and Kaars Sijpesteijn observed a dramatic influence on fungicidal activity of the number of direct t i n carbon bonds (Table I).

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch008

Table I Antifungal Activity of Ethyltin Compounds Minimum concentrations in mg/1 (ppm) causing complete growth inhibition. Peptone glucose agar, pH 6.4; 2 4 ° ; 3 days.

.-Butt. allii

Et Sn 4

Et SnCl 3

Et SnCl 2

EtSnCl SnCl \ 2

3

2

Pen italicum t

Asp. niger

Rh. nigricans

50

;>iooo

100

100

1

10

2

2

>1000

>1000

>1000

^>1000

>1000

^1000

>1000

;>iooo

>>1000

J>1000

^>1000

^>1000

SnClJ It thus appeared that only triethyltin chloride exhibited high antifungal activity, the other types being much less active or inactive, like the inorganic tin compounds. Replacement of chloride by other anionic groups either inorganic or organi c , in general had no significant effect on the in vitro activity*. Nevertheless some prudence should be exercised in this respect as will be shown later o n . Next, Luijten prepared a series of tri-substittuted organotin acetates, which were tested for antifungal activity by Kaars Sijpesteijn. (Table II) * Such groups, which do not involve direct tin-carbon bonds, may, however, be of significance in practical formulations.

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Table II Antifungal Activity of Triorganotin Acetates Minimum concentrations in mg/1 (ppm) causing complete growth inhibition. Peptone glucose agar, pH 6.4; 2 4 ° ; 3 days.

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch008

R SnOCOCH R= Methyl Ethyl _n-Propyl J.-Propyl n-Butyl i-Butyl n-Pentyl Cyclo-pentyl n-Hexyl Cyclo-hexyl n-Octyl Phenyl

Botr. allii 200 1 0.5 0.1 0.5 1 5 0.5 j>500 20 >500 10

Pen. italicum

Asp. niger

500 10 0.5 0.5 0.5 1 2 0.5

200 2 0.5 1 1 10 5 5 ^>500 50 >'500 0.5

:>5oo 20 >500 1

Rh. nigricans 500 2 0.5 1 1 1 5 0.5 >>500 20 >500 5

Here again, a dramatic effect, be it of a different kind, became apparent. Among the trialkyltin compounds, the propyl and butyl derivatives classified themselves at once amongst the most powerful fungicides known. Also the ethyl, pentyl and cyclo-pentyl derivatives showed high activity. The trimethyltin and in particular the tri-n-hexyl- and t r i - n octyltin compounds were notably inactive. Triphenyltin acetate exhibited moderate to high activity. These results at once suggested a number of possibilities for practical applications, in the first place of course as fungicides, but, on the basis, of anticipated wider b i o c i d a l , in particular antimicrobial effects, of quite different biocidal applications as w e l l . These expectations have been fulfilled remarkably w e l l . Later on in this paper I shall briefly survey the present-day applications of organotin compounds as fungicides and as biocides in a more general sense. This early explorative work was continued along three lines: 1. As has already been said before, no truly functionally-substituted organotin compounds - i . e . ,

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compounds carrying functional groups like O H , OR, NH2, N R , C O O H , COOR, etc. - were known. Since in organic compounds the presence of such groups is of outstanding significance for their physiological properties, it was decided to look for ways to synthesize functionally-substituted organotin compounds and to study their fungitoxicity.

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch008

2

2.

The work was extended to the study of corresponding organo-germanium and -lead compounds and broadened to include a wider series of test fungi.

3.

The work was extended to the study of the bactericidal effects of organogermanium, -tin and lead compounds.

A few words will be said about the results of each of these lines of approach. ad

1.

At Utrecht in the mid-fifties, Dr. J . G . Noltes (5) succeeded in finding an elegant solution for the synthesis of functionally-substituted organotin compounds. I discussed his early work at another session of this Centennial Meeting. Subsequently, his compounds were tested for fungicidal activity. Some of the results are shown in Table III. Much to our surprise - and contrary to experience in general organic chemistry - the introduction of functional substituents in organic groups attached to tin did not modify antifungal activity - e . g . , by causing shifts in specificity or changes in the mode of action but instead abolished it. This was not only a disappointing observation but a challenging one as w e l l . The disappointment is over, but the challenge has remained, since so far we have not been able to find a reasonable explanation (Table III).

ad

2.

In Utrecht a tremendous amount of effort was spent the preparation of representative series of organogermanium and -lead compounds and to the study of their antifungal and antibacterial properties. Only a few results will be mentioned here. Under this section some comparative figures will be given regarding the fungicidal activity. In the next section o n

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the bactericidal properties will be mentioned. Table IV summarizes the activities of the several types of organogermanium, - t i n and -lead compounds containing ethyl, n-butyl and phenyl as the organic groups. Table III Antifungal Activity of Functionally-Substituted Orqanotin Compounds

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch008

Minimum concentrations in mg/1 (ppm) causing complete growth inhibition. Peptone glucose agar, pH 6.4; 2 4 ° ; 3 days. , Compounds

Botr. τ—*· allii

Pen. .' italicum

Ph SnCH CH COOMe

>500

>500

•^>500

J>500

Ph SnCH CH COOH

:>100

>100

>100

>100

20

100

50

100

0

^Sn 3

2

3

2

2

2

Prop SnCH CH CH NH 3

2

2

2

2

Prop Sn(CH CH COONa) 2

2

2

PropSn(CH CH COONa) 2

2

3

2

Asp. , niger

Rh. .—— nigricans

>100

r>100

:>100

>100

200

:>500

>500

>500

^50

50

>50

>50

R SnX 3

Ph ( C H C H C N ) S n I 2

2

2

Ph Sn CH CH COO"

^>100

100

50

>100

Bu Sn CH CH COO"

>100

:>100

^>100

>100

5

50

50

50

50

:>50

->50

^>50

2

2

+

2

+

2

2

2

Bu SnCH CH COOMe(Br) 2

2

2

PhSnCH C H CN(Br )

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PESTICIDE C H E M I S T R Y I N T H E 2 0 T H

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Table IV Antifungal Activity of Corresponding Organogermanium, - T i n and -Lead Compounds Against Aspergillus Niger (Minimum concentrations in mg/1 (ppm) causing complete growth inhibition) Ge

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch008

Types

Pb

Bu

Ph

Et

^>500

>500

>500

^>590

50

>500

>500

2

1

R MX >500

^500

>500

^500

^>500

10

RMX >500

^500

^ 500

^500

^>500

500

R.M 4

Et

Sn

R MX 3

2

2

3

Bu

Ph

>500 ^500 0.5

Et

J3u„_Ph

^500 ^500->500 20 ^500 +)

0.5 20 +)

2 50

200

Here again, it appears that highest activity for germanium, tin and lead is connected with the structural type R 3 M X . However, the activity of the germanium compounds is negligible and the activities of the tin and lead compounds of this type are high and of the same order of magnitude. For lead, but not for t i n , also the dibutyl compound is fairly active. For phenyl, it is just the other way around. In Table V a summary is given of the antifungal activities of compounds R M X for germanium, tin and lead and for different kinds of groups R (X being acetate throughout). 3

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Table V Antifungal Activity of Tri organogermanium, - T i n and -Lead Acetates (Minimum concentrations in mg/1 (ppm) causing complete growth inhibition)

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch008

MOAc R Methyl Ethyl n-Propyl n-Butyl n-Pentyl Phenyl

Botr. allii

Pen. italicum

Asp. niger

Rh. nigricans

;>500 50 50 >500 ::>500 >500

^500 200 >500 ^>500 ---500 ^500

-^500 50 50 ->500 ^500 ^500

•^500 200 100 >500 ^>500 ^500

200 1 0. 5 0. 5 5 ^>500 10

^>500 10 0.5 0.5 2 >500 1

200 2 0.5 1 5 ^500 0.5

^500

Methyl 100 Ethyl 20 η-Propyl 2 jv- Butyl 0. 1 jv-Pentyl 0. 1 jl-Hexyl 0. 5 jv-Heptyl 50 ji-Octyl :>500 2 Phenyl

200 20 5 0.5 0.2 2 100 >500 2

200 20 10 0.5 0.5 2 100 >500 2

Methyl Ethyl n-Propyl n-Butyl n-Pentyl JOL-Hexyl Phenyl

2 0.5 1 5 ^>500 5 ^500 50 5 0.5 0.5 100 >500 ^>500 5

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Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch008

To make things a little bit better surveyable the results for the alkyl compounds are given in a graphical form ( F i g . l ) .

I

ι 2ι 3ι 4ι 5. 61

I R = Me

Et

Pr

Bu

Pen

Hex

7 Hep

ι8 Oct

Figure 1. Influence of chain length of trialkylsubstituted germanium, tin, and lead acetates on minimum concentration inhibitory to Aspergillus niger. , germanium; - · -, tin; , lead.

The overall activity of the triorganotin and -lead compounds is about the same, that of the germanium compounds is much lower. Optimum activity for germanium occurs with ethyl and propyl, for tin with propyl and butyl, and for lead with butyl and pentyl substituents. There was little or no influence of the composition of the nutrient medium nor of its pH on activity. Later on it was found by Kaars Sijpesteijn (6] that certain fungi are considerably more sensitive to trialkylgermanium compounds (e.g. Debaryomyces nicotianae, Trichophyton mentagrophytes and Glomerella cinqulata). A few related organosilicon com­ pounds (R = Ethyl, Butyl and Phenyl) were found to be com­ pletely inactive, even against a few fungi which had been found to be highly sensitive to triethylgermanium acetate.

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Later on our results were extended, in particular with regard to phytopathogenic fungal species, by several other workers. This extension has resulted in the present-day practical applications of organotin compounds as biocides. As a general conclusion, it can be stated that thus far, a l l fungi tested, whether belonging to the Phycomycetes, the A s comycetes, or the Basidiomycetes have been found to be susceptible to certain types of tri-substituted organotin compounds . For more detailed information, also on mixed alkyl and mixed alkyl-aryl compounds, I may refer to a review article Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch008

m. ad

3.

In this section results are summarized which have been obtained at Utrecht with the structural types R 3 M X and R 2 M X 2 against five characteristic bacterial species. The following organisms were used: the gram-positive species Bacillus subtilis, M y c o bacterium phlei and Streptococcus lactis, and the gram-negative species Escherichia coli and Pseudomonas fluorescens. Some data are given in Tables VI, VII and VIII. Table VI Antibacterial Activity of Compounds I^GeX and I^GeXo (min. concentrations in mg/l(ppm) causing complete growth inhibi.) Gram-negative Gram-positive E_. Ps_. Compounds subtilis phlei lactis coli fluoresce Me^GeOAc

>500

^500

Et^GeOAc

^>500

^500

50

Prop GeOAc

^>500

20

Bu GeOAc

:>500

Pent GeOAc

>500

>500

^500

^>500

5

:>500

:>500

2

1

>500

^500

:>500

5

2

>500

^>500

Hex^GeOAc

^>500

•^500

20

^>500

:>500

Ph GeOAc

^>500

^500

^500

^>500

^>500

Et GeCl

^>500

^500

^>500

>500

^>500

3

3

3

3

2

2

^500

Bu GeCl

2

^500

>>500

^500

> 500

^500

Ph GeCl

2

^500

^500

^-500

^500

^>500

2

2

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PESTICIDE C H E M I S T R Y IN T H E 2 0 T H

Table VII Antibacterial Activity of Compounds R^SnX and R^SnX,

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch008

(Minimum concentrations in mg/1 (ppm) causing complete growth inhibition)

Compounds

Gram-positive M. _S_. JLphlei lactis subtilis

Me SnOAc

>500

>500

50

10

3

Et SnOAc 3

>500 100

Gram-negative Ps. coli fluoresce >500

^>500

20

20

Prop SnOAc 3

2

0 .2

5

50

20

Bu SnOAc

2

0 .1

5

^>500

100

Pent SnOAc

5

0 .2

10

>500

>500

Hex SnOAc

50

10

50

^>500

>500

Hep SnOAc

>500

^>500

500

^>500

>500

^>500

:>500

3

3

3

3

Ph GeOAc

0.5

3

Me SnCl 2

Et SnCl 2

2

2

Prop SnCl 2

Bu SnCl 2

2

Pent SnCl 2

Hex SnCl

2

Hep SnCl

2

2

2

Ph SnCl 2

2

2

2

0 .1

5

200

200

500

500

200

50

100

200

100

100

20

50

50

50

50

20

20

20

20

^>500

20

20

50

500

50

100

>500

>500

>500

^500

>500

->500

>500

>500

>500

20

5

50

>500

>500

CENTURY

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Table VIII Antibacterial Activity of Compounds

R^PbX and R

2

P b X

;

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch008

(Minimum concentrations in mg/1 (ppm) causing complete growth inhibition)

Gram positive M. S. phlei lactis subtilis

Compounds

Gram-negative E. Ps. coli fluoresce

100

100

200

200

100

50

50

50

50

20

Prop PbOAc

2

2

2

5

10

Bu PbOAc

0.5

0.2

1

20

20

Pent PbOAc

0.5

0.1

5

50

50

Hex PbOAc

5

0.2

10

>500

>500

Hep PbOAc

20

5

>500

>500

Oct PbOAc

50

20

>500

^>500

Me PbOAc 3

Et PbOAc 3

3

3

3

3

3

3

200

Ph PbOAc

1

0.05

1

20

50

Me PbAc

0.2

0.2

1

50

50

0.2

1

5

5

5

0.2

0.2

0. 5

1

2

0.1

0.1

0. 2

1

10

0.2

0.2

0. 5

2

500

0.5

0.5

1

5

2

2

10

100

>500

20

20

50

>500

>500

1

2

1

10

3

2

Et PbAc 2

2

2

Prop PbAc 2

Bu PbAc 2

2

2

Pent PbAc 2

Hex PbAc 2

2

Hep PbAc 2

Oct PbAc 2

Ph PbAc 2

2

2

2

2

>500

100

PESTICIDE C H E M I S T R Y IN T H E 2 0 T H C E N T U R Y

142

From tables VI-VIII, the following generalized conclusions can be drawn:

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch008

-

with two exceptions the bacteria were insensitive to both types of germanium compound gram-positive species are more sensitive to the organotin and -lead compounds than gram-negative species for tin the dialkyl compounds are generally less active than the trialkyl compounds; for lead rather the reverse is true, in particular against the gram-negative species. In fact, certain dialkyllead compounds are surprisingly active and belong to the most potent antibacterial agents known. A presentative triethylsilicon compound was found inactive against all bacterial species investigated. Here again, for details I must refer to the review article mentioned (4). A few remarks may be made on the mode of antifungal action of tri- and disubstituted organotin and -lead compounds. Very little direct information is available in this respect. Early observations indicated that a profound difference does exist between the biochemical modes of action of triorganotin and -lead compounds on the one hand and diorganotin and -lead compounds on the other. Whereas the latter compounds are antagonized by thiol compounds, in particular by the d i thiol compound 2,3-dimercaptopropanol (BAL), no single antagonist is known of the triorganotin and -lead compounds. On the basis of studies by Aldridge (7]_ on the mammalion toxicity of triorganotin (and -lead) compounds it is now generally accepted (cf 4) that these compounds effectively interfere with oxidative phosphorylation and block a reaction step in the energy-transferring chain leading to ATP formation. The variations in antifungal activity within the series of homologous trialkyltin and -lead compounds may be due both to differences in intrinsic activity of the compounds at the enzymic site, and to permeability differences for the several compounds . In this latter respect the relation between water- and lipid-solubility of the compounds will be of importance. According to Barnes and Stoner _(8} dialkyltin (and -lead) compounds in mammalian systems are inhibitors of the enzymes ok-keto acid oxidases by interference with the physiological function of a dithiol compound, the coenzyme -lipoic a c i d . The same mechanism may apply for the antimicrobial activity of these compounds. It remains, however, remarkable that their antifungal activity is rather low, whereas in particular

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certain dialkyllead compounds are extremely powerful bactericides. One possible explanation may be a considerable difference in the capacities for cell penetration, (c f 9). In the early part of my paper, I referred to the work of Voronkov _(3J regarding the physiological effects observed by him for a series of organosilicon compounds. A particularly intriguing observation was the high mammalian toxicity of the compound phenylsilatrane. This compound can easily be obtained from phenylsilicon trichloride and triethanolamine:

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch008

PhSiCl

3

+ (HOCH CH ) N 2

2

> PhSiiOCK^CH^N

3

Structurally the compound is highly interesting since it is a tricyclic cage compound, containing one silicon-carbon bond, three silicon-oxygen bonds and one silicon-nitrogen coordination bond, resulting in a very stable penta-coordinated organosilicon structure: 11

X Voronkov also prepared the corresponding germanium compound phenylgermatrane. For this compound he observed a very low mammalian toxicity. Both phenylsilatrane and phenylgermatrane had negligible antimicrobial activity. Since at Utrecht significant biological activity had never been observed for any mongorganotin compound, we prepared the tin-analogue phenylstannatrane and tested it on antifungal and antibacterial activity. To our surprise phenylstannatrane showed appre-

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Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch008

ciable fungitoxicity but was completely inactive again both gram-positive and gram-negative bacteria. It is not possible to draw general conclusions from these observations, but it should be clear that biological activity of fourth main group (organo)metal compounds may depend as well on some factors which are as yet unknown and which are possibly related with the occurrence of certain types of coordination structures with very specific molecular geometries. Here, in my opinion, a field for further explorative research lies wide open. Antimicrobial Activity of Organometallic Compounds of Antimony and Bismuth Arsenic, antimony, and bismuth are the metallic representatives among the fifth main-group elements. Owing to early chemotherapeutic applications a tremendous number of organometal derivatives has been prepared, especially of arsenic. Both in their inorganic and their organic compounds these metals can occur in the trivalent or in the pentavalent state. Consequently the following types of organometallic compounds are known: Trivalent

R^M

Pentavalent

R^M

R MX

RMX

2

R

3

M

X

R

2

2

M X

2

3

R M X

4

R and X have the same meaning as indicated before. In these compounds the metal-carbon bonds are highly covalent and chemically rather stable. The chemical reactivity of the trivalent compounds, in particular those of the type R 3 M is associated with an easy oxidizability to the pentavalent state rather than with rupture of metal-carbon bonds. Thus, the vigorous reaction of the trialkyl compounds R 3 M with air depends on the following oxidative transformation: RgM

> R MO 3

On the other hand, under reducing conditions the pentavalent compounds are easily converted into the trivalent ones. This is of importance since the biological properties within this group seem to be associated with the trivalent state.

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For reasons mentioned before, only the antimicrobial activity of organoantimony and -bismuth compounds will be presented here. The results have been taken from a paper of Beiter and Leebrick (10) and are summarized in Table IX. Table IX Antimicrobial Activity of Organoantimony and -Bismuth Compounds

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Fungi Pen. fumçuCompounds losum Antimony R Sb Prop^Sb >500 Bu-Sb 125 Ph Sb >>500 R SbCl Ph SbCl 125 RSbClo 250 PhSbCl2 R3SbCl P h S b C l ">500

Asp. flavus

Cand. albicans

Bacteria Gram Gram + Ps. _A_. Staph. aerugaerogenes aureus inosa

3

3

^500 250 ^500

250 63 >500

16 5 >500

31 31 ^>500

125 63 ->500

2

250

31

2

4

4

250

63

2

8

4

^>500

>500

63

>>500

^500

250 ^500

63 >500

0.5

4 ^>500

2 ^>500

0.5

4

2

8 2

2 2

31

31

2

9

3

2

Lsmuth Bu Bi 250 Ph Bi ^>500 R BiCl P h B i C l ^>500 RBiCl 500 BuBiCl PhBiCl :>500 R BiCl P h B i C l >500 3

3

^500

2

2

^500

63

^500 ^500

125 63

0.5 0.125

^500

125

8

2

2

2

3

2

3

2

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PESTICIDE C H E M I S T R Y IN T H E 2 0 T H C E N T U R Y

From this Table, it is evident that the antifungal activity of both organoantimony and -bismuth compounds is very low to negligible. As bactericides they are clearly more active, the structural types R 2 M X and RMX being even highly active. It should be noted that published information on the antifungal and antibacterial activity of organoantimony and - bismuth compounds is much less complete than that a v a i l able for the fourth main group elements. Although suggestions have been made for potential uses of organoantimony and -bismuth compounds as antimicrobial agents and undoubtedly much more extensive work has been done than has been published, it can be stated that no single compound has reached the market place. For that reason, I restrict my discussion of these compounds to the few facts mentioned.

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2

In summary, it would seem that the evidence resulting from the fundamental studies of structure-activity relationships indicate only certain triorganotin compounds as biocides of potential practical significance. This, in fact, has become true in a remarkable way. In my paper "Organotin Chemistry. Past, Present and Future", presented during this same C e n tennial Meeting, I have reviewed a l l present-day practical applications of organotin compounds. To conclude my present paper, I will briefly summarize the applications of certain triorganotin compounds as fungicides. Fungicidal Applications of Tributvltin and Triphenvltin pounds *

Com-

Our original observations regarding the very high antifungal activity of the lower trialkyltin and of triphenyltin compounds raised the expectation that these compounds might be generally useful protectant agricultural fungicides. Because of their broad antifungal spectrum, it was anticipated that they would be suitable for the combat of a wide variety of fungal plant diseases. This broad expectation has not become true. Independent work of Hërtel (Farbwerke Hoechst, Germany) (12) showed that in the laboratory trialkyl- in particular tributyltins are better fungicides than triaryltin compounds, but that the reverse is true in the f i e l d . This has been ascribed * For an extensive review on all present organotin applications, see Luijten (11).

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to the lower stability and the higher volatility of the former. Moreover, triaryltin compounds are less phytotoxic than trialkyltin compounds. The final result has been that now certain triphenyltin formulations - containing either triphenyltin h y ­ droxide or acetate - have become important agricultural fungi­ cides . Their importance is not connected with their general usefulness but with their specific effectivity against two economically extremely important plant diseases, v i z . late blight of potatoes, caused by Phytophthora infestans, and leaf spot in sugar beets, caused by Cercospora beticola. In these applications, they have in Europe almost completely ousted the formerly dominating inorganic copper compounds. Later on it was found that also a number of important tropi­ cal plant diseases - v i z . in coffee, rice, ground nuts, banana and pecan - can be successfully controlled. A further exten­ sion of the triphenyltin compounds as agricultural fungicides was found in their combination with manganese ethylenebisdithiocarbamate (maneb). A particular advantage of triphenyltin formulations i s , that so far no development of field resistance has ever been observed. The problem of toxic residues from field sprays with tri­ phenyltin compounds has been very thoroughly investigated. An important feature is the relatively short half life of these compounds on the foliage under field conditions ( 3 - 4 days). Moreover the compounds do not penetrate into the plant and their action is thus purely protective. In summary, it may be said that the agricultural applica­ tions of organotin compounds as fungicides so far are restric­ ted to a comparatively small, though very important, number of plant diseases and pests. Moreover, on the basis of the more recent developments and because tin compounds in several cases are fully active against resistant varieties, it may be expected that a further modest growth of the uses of organotins in agriculture is likely to occur. Another agricultural development of great potential inter­ est is based on the more recent observation that certain rather unusual triorganotin compounds have considerable acaricidal activity. Well-known at present is the compound t r i cyclohexyltin h y d r o x i d e (trade name "Plictran") developed by Dow Chemical Company and Μ & Τ Chemicals. This com­ pound is very effective against spider mites in fruit orchards and has been found to act as well against varieties of spider mites which had developed resistance towards the usual acaricides based on organic phosphorous compounds and car-

American Chemical Society Library

1155 16th St. N. w. Washington, D. C. 20036

148

PESTICIDE C H E M I S T R Y IN T H E 2 0 T H C E N T U R Y

bamates. Another promising compound with a similar application field is marketed by Shell. It is the compound trisneophyltin acetate,

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch008

CH,

Whereas the trialkyltin compounds have not succeeded as agricultural fungicides, one particular tributyltin compound, v i z . bis (tributyltin) oxide (TBTO): (C H ) SnOSn(C H ) 4

9

3

4

9

3

has become notoriously successful as a general biocide, in materials protection, in particular in wood and paint preservation, as an antifouling agent and as a surface disinfectant. The origin of these applications stems entirely from the early work at Utrecht by Luijten and Kaars Sijpesteijn, which I already cited before. Among the first publications on the preservation of wood against fungal attack by means of triorganotin compounds were those of Hof and Luijten (TNO) (13]_ and of Fahlstrom (14). Since then, wood-preservation using TBTO as or among the active ingredients has become common practice. Tributyltin compounds are characterized by their high activity and broad antifungal spectrum. Their leachability by water is extremely low and they have the advantage of being colorless and noncorrosive. Amounts of 0.5 - 2kg of TBTO per m of wood are quite effective not only against fungal decay but as well against the attack by marine borers: shipworms (Teredo) and gribble (Limnoria). Much higher concentrations are required to protect wood against wood-boring insects such as the common furniture beetle and in particular termites, and here combinations with other active ingredients, in particular insecticides, are required. 3

An excellent review on TBTO-based wood preservatives has been given by Richardson at the 1970 Annual Convention of the British Wood preservers Association (15). The low aqueous leachability of TBTO is due to its high affinity in particular to cellulose. As a consequence, how-

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ever, its penetration into deeper layers of the treated wood poses some problems. To a certain extent these have been solved by the use of special impregnation techniques and also by combining organtins with other biocidal agents which have better penetrating properties. During the past few years, our group at Utrecht, in cooperation with the Wood Research Institute TNO at Delft, has developed a different approach. The

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h y d r o c a r b o n - l i k e compound h e x a b u t y l d i t i n BugSnSnBu^, w h i c h i s

very soluble in non-polar hydrocarbon solvents, was found to have much better wood-penetrating properties than TBTO, but to equal this compound in wood-pre serving capacity. We believe that hexabutylditin offers considerable promise as a new wood-pre serving agent, provided that a satisfactory method can be developed for its technical manufacturing. Interesting and rather surprising is the claim, made in a recent patent application (16) that monobutyl- and monoctyltin compounds are effective wood preserving agents, notwithstanding their negligible in vitro fungitoxicity. It is suggested that these compounds effectively block places within the wood which are vulnerable to fungal attack. Triorganotin compounds, in particular TBTO and tributyltin fluoride, are finding increasing use in marine antifouling paints (cf 17). An interesting application where organotins may s u b s t i t u t e f o r o r g a n o m e r c u r i a l s is p a i n t p r e s e r v a t i o n , a l t h o u ­ gh a f e w c o m p l i c a t i o n s h a v e to b e s o l v e d . For instance, the

antimicrobial spectrum of triorganotins, though considerable, is not so wide as that of the organomercurials. To reach an equivalent degree of protection, new formulations have to be developed which in certain cases must contain other active ingredients as w e l l . One notable deficiency of TBTO is its modest activity against gram-negative bacteria. It has been found in Utrecht that tripropyltin compounds have a wider antibacterial spectrum and are rather active against gram-negative bacteria as w e l l . A modest but important use of certain tributyltin-containing formulations is in hospital and veterinary disinfectants. Similar formulations are applied to protect textiles against fungal and bacterial attack, both in the industrial and the hygienic sector ("sanitizing"). In reconsidering the biocidal properties of organotin compounds, one cannot get away from the conclusion that the biocidal applications are likely to expand strongly in the future, both as a result of an extension of the present possibilities and of the development of new ones.

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PESTICIDE C H E M I S T R Y IN T H E 2 0 T H C E N T U R Y

Much will depend here on the outcome of the present study of the metabolic fate of organotin compounds under environmental conditions. It is generally accepted that the basic types of organotin compounds are subject to the following generalized pattern of physical, chemical and/or biochemical degradation: or SnX resp.

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0

which ultimately leads to non-toxic inorganic forms of t i n . Until recently, there was very little evidence for the actual course and rates of such degradation processes under environmental conditions. The overall toxicity picture for any compound i s , however, dependent both on its own toxicity and on the toxicity of the degradation products formed under the conditions of its application. To f i l l this gap, a joint programme was started some years ago at the Institute for Organic Chemistry TNO at Utrecht under the final responsibility of the Tin Research Institute. This programme - the Organotin Environmental Project, or ORTEP - is supported by about ten major organotin-producing companies a l l over the world. Conclusion Among the 92 naturally-occurring elements listed in the periodic table, 75 are considered metals. My review has shown that on the basis of present knowledge and on that of presently accepted standards only the organometallic compounds of tin are likely to have a future as fungicides, and, in a wider sense, as general biocides. This is a meagre conclusion which nevertheless is founded on a considerable amount of evidence. Of course, a larger number of metals, in particular transition metals, is of practical significance in a number of fungicidal applications, either in inorganic forms like copper - or in combination with organic molecules known to have fungicidal activity - like iron, zinc and manganese in the dithiocarbamates. In the latter, the metals do not, as far as we know, contribute to the intrinsic fungitoxicity of the compounds in question, but their function is nevertheless i m portant, so to say as built-in formulation factors which modify the chemical and biological characteristics of their ligand molecules. One particular aspect has not yet been discussed. In organometallic compounds in the first instance, we must forget

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Fungicides

about the underlying metal. I will illustrate this for t i n . Let us look again at the basic types of organotin compounds: R Sn

R SnX

4

S

2

n

X

RSnX

2

3

in which only the groups X are easily interchangeable. As long as no tin-carbon bond ruptures occur, we are dealing with the units R^Sn RSn . Whatever the proper­ ties of these units are, these are completely different from those of S n , S n or S n , i . e . from metallic or inorganic tin, and, in fact, have very little to do with the latter. Ulti­ mately, R3Sn , R 2 S n and R S n must be considered as ions of completely different "metals", not only mutually different but also different from the ions S n and S n ^ . Here lies the ultimate clue to the understanding of both the tremendous differences between the several basic types of organotin com­ pounds and of the profound influence of the organic groups R on the properties of the individual types. In organotin com­ pounds , it is not tin which defines their ultimate properties, but its combinations with different types and numbers of firmly bound organic substituents. What has been explained for tin is appropriate for all organometallic compounds containing stable to reasonable stable metal-carbon relations. R

3

2 +

+

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R

3

S

n

+

a

n

d

3 +

4 +

2+

3 +

2 +

+

Literature Cited 1. (a)

Janssen, M . J . , a n d Kaars Sijpesteijn, Α., S.C.I. Mono­ graph, London, (1961), 15, 40. (b) Kaars Sijpesteijn, Α., and Van der Kerk, G.J.M., Proc. 5th Brit. Insect and Fung. C o n f . , (1969), 724.

2. 3. 4.

5. 6.

Van der Kerk, G.J.M., Pluygers, C . W . , a n d De V r i e s , G . , Rec. Trav. Chim. Pays-Bas, (1955), 74, 1262. Voronkov, M.G., Chemistry in Britain, (1973), 9, 411. cf Kaars Sijpesteijn, Α . , Luijten, J . G . A . and Van der Kerk, G.J.M., "Fungicides, An Advanced Treatise", chap. 7, II, Academic Press, New York and London(1969) Van der Kerk, G.J.M.,and Noltes, J.G., J. App. C h e m . , (1959), 9, 113. Ibid (1959),9, 176. Ibid. (1959), 9, 179. Kaars Sijpesteijn, Α., Rijkens, F., Van der Kerk, G.J.M., and Manten, Α . , Antonie van Leeuwenhoek J . M i c r o b i o l . Serol. (1964), 30, 113.

152 7. 8. 9. 10. 11. 12.

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13. 14. 15. 16. 17.

PESTICIDE CHEMISTRY IN THE 20TH CENTURY Aldridge, W. N. and Street, B. W., Biochem. J. and references cited therein, (1964), 91, 287. Barnes, J. M. and Stoner, Η. Β., Pharmacol. Rev., (1959) 11, 211. Kahana, L., Kaars Sijpesteijn, Α . , Antonie van Leeuwenhoek J. of Microbiol. and S e r o l . , (1967), 33, 427. Beiter, C. B. and Leebrick, J. R., Chem. Specialties Mfrs. Assoc. (cf 4), (1963), 49, 132. Luijten, J. G. Α . , "Organotin Compounds", chap. 12, Marcel Dekker, I n c . , New York, 1972. H ä r t e l , Κ . , Agr. Vet. Chem., (1962), 3, 19. (See also: H ä r t e l , Κ . , Tin and its Uses, (1958), 43, 9 and (1963), 61, 7). Hof, T. and Luijten, J. G. Α . , Timber Technology, (1959), 67, 83. Fahlstrom, G. Β., Proc. Am. Wood - Preservers' Assoc., (1958), 54, 178. Richardson, Β. Α . , British Wood Preservers' Assoc., Annual Convention, (1970). Germ. Offenl. 2.351.188 to Albright & Wilson Ltd. (Oct. 13, 1972 - May 9, 1974). Evans, C. J., Tin and its Uses, (1970), 85, 3 and (1973), 96, 7. Evans, C. J. and Smith, P. J., J. O i l Col. Chem. Assoc. (1975), 58, 160.

9 The Sulfenimide Fungicides GUSTAVE Κ. KOHN

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch009

Zoecon Corp., 975 California Ave., Palo Alto, Calif. 94304

H i s t o r i c a l Introduction Shortly after World War II, a research chemist at the Stan­ dard O i l Development Company (Esso) s t r o l l e d into an oil additive laboratory and saw an interesting intermediate c a l l e d perchloro­ methyl mercaptan (CCl SCl). A. F. K i t t l e s o n , spurred by v i s i o n s of the trichloromethyl group i n that then new miracle drug DDT, decided to try some reactions with the above described s u l f e n y l halide. He synthesized a multiplicity of new compounds (1) (2) (3) and discovered a unique series which contained the Ν - S bond. Unfortunately these structures possessed no i n s e c t i c i d a l p o t e n t i a l whatsoever. Fortunately, however, certain of these compounds were directed to a plant pathologist at Rutgers University, Dr. Robert H. Daines, (4) (5) (6) who noted exceptional fungistatic and fungicidal properties. If chance was involved in t h i s discovery, let it be empha­ sized that it is a component in all inventions (7), and t h i s one proved in time to be highly s i g n i f i c a n t . Subsequent development and derivative invention (8) and discovery have provided biocides used i n this country, i n the agriculture of all the developed countries, i n much of undeveloped A s i a , L a t i n America and A f r i c a , and i n the Communist domains throughout the globe. The present i n s t a l l e d capacity over the world for sulfenimide group fungi­ cides i s estimated as above 50 m i l l i o n lbs but less than 100 m i l l i o n lbs/year. Thus the conception of t h i s discovery; the gestation i n the early period was difficult and troubled. In the beginning of this century, perchloromethyl mercaptan was considered (and had been given a b r i e f trial as) a war gas. There was little ex­ perience with its use by industry. The cost projections and the 3

The content of t h i s paper derives from t h i r t y years association with the Research Department of Chevron Chemical Company, Richmond, C a l i f o r n i a .

153

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a c t u a l m a n u f a c t u r i n g c o s t s f o r t h e e a r l y p r o d u c e d c a p t a n was a p p r o x i m a t e l y f i v e u n i n f l a t e d d o l l a r s p e r pound. The f i r s t p r o ­ d u c t i o n employed a D D T - l i k e b a t c h c o n d e n s a t i o n . The p r o d u c t t h a t was o b t a i n e d was o d o r i f e r o u s , c o r r o s i v e , e x p e n s i v e and o f q u i t e doubtful exploitable potential. F o r two c o n s e c u t i v e y e a r s , l a r g e a r e a s o f a p p l e o r c h a r d s i n New J e r s e y ( a p p l e s c a b , V e n t u r i a i n a e q u a l i s i n f e c t i o n was a p r i m a r y t a r g e t a t t h a t time f o r t h e s e f u n g i c i d e s ) were a l m o s t t o t a l l y d e f o l i a t e d and many f a v o u r e d abandonment o f t h e d e v e l o p m e n t p r o ­ ject. No more names w i l l be m e n t i o n e d i n t h i s h i s t o r y b u t c h e m i s t s and c h e m i c a l e n g i n e e r s f o u n d ways t o make t h e i n t e r ­ m e d i a t e s , t o p u r i f y t h e p r o d u c t and f i n a l l y t o p r o d u c e c a p t a n , a f u n g i c i d e ^ a t a c o s t comparable to the l e s s expensive s y n t h e t i c p e s t i c i d e s of t h a t p e r i o d - a l l b e f o r e the r i s e of crude o i l p r i c e s , s h o r t a g e o f i n t e r m e d i a t e s and s u b s e q u e n t runaway i n f l a ­ t i o n d i s t o r t e d manufacturing economics. B i o l o g i s t s d i s c o v e r e d how and when t o use t h e s e f u n g i c i d e s and p a r t i c u l a r l y t h e c r i t i c a l p e r i o d s t h a t d e f i n e d and c i r c u m ­ s c r i b e d t h e i r u s e f u l n e s s and p r a c t i c a l s a f e t y . F i n a l l y , t h r o u g h t h i s l o n g c o n c e p t i o n and g e s t a t i o n p r o c e s s , t h e r e w e r e company e x e c u t i v e s who had t h e v i s i o n and t h e c o u r a g e t o v e n t u r e c a p i t a l and s u p p o r t a l l t h e n e c e s s a r y p h a s e s o f t h e d e v e l o p m e n t , d e s p i t e c o n s i d e r a b l e periods of discouragement. S i n c e t h a t p e r i o d , new s e r i e s o f compounds w e r e d i s c o v e r e d ( e g . D i f o l a t a n ® (8) and a n a l o g u e s ) and c o m p o s i t i o n s p o s s e s s i n g p r a c t i c a l f u n g i c i d a l , b a c t e r i c i d a l , a l g i c i d a l and m e d i c i n a l p r o p e r t i e s (9) h a v e f o u n d a broad a p p l i c a t i o n throughout the w o r l d . Structural

Definition

The s u l f e n i m i d e f u n g i c i d e s may be s t r u c t u r a l l y d e f i n e d as i n F i g u r e 1. The f o r m u l a g i v e n i s q u i t e g e n e r a l and p r o v i d e s f o r an immense number o f s y n t h e t i c v a r i a n t s . R and R may be r i n g s (homocyclic or h e t e r o c y c l i c , aromatic, or of v a r i o u s degrees of s a t u r a t i o n and u n s a t u r a t i o n , s u b s t i t u t e d o r u n s u b s t i t u t e d ) o r chains of m u l t i p l e types. R and R can be p a r t o f a s i n g l e r i n g . Whether r i n g o r c h a i n , a t l e a s t one s u l f o n y l , p h o s p h o r y l o r c a r b o n y l group ( e t c ) i s v i c i n a l to the n i t r o g e n . This a f f e c t s t h e c h a r a c t e r o f t h e t r i v a l e n t n i t r o g e n so t h a t t h e i n t e r m e d i a t e R ( R ) N H i s p r e f e r e n t i a l l y w e a k l y a c i d i c w i t h pKa's f r e q u e n t l y i n the p h e n o l i c range. R i s a s h o r t c h a i n p o l y h a l o a l k y l o r a l k e n y l group. Most f r e q u e n t l y t h e h a l o g e n s a r e C I , B r and F o r m i x t u r e s o f them. Many o t h e r N-S compounds may be and h a v e b e e n p r e p a r e d b u t t h e f o r m u l a i n F i g u r e 1 g e n e r a l i z e s f o r t h o s e w i t h u s e f u l and p r a c t i ­ cal antifungal properties. T

1

f

1

1

9. κοΗΝ

The Sulfenimide

Fungicides

155

R ^ N - S - R " R' R and R' may be cyclic including part of same ring or separate rings or chains. These contain at least one carbonyl, sulfonyl, phosphonyl etc. group.

\ The intermediate

Ν - Η is preferably a weak acid.

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch009

R' R" is a short chain polyhaloalkyl or alkenyl group. Halogens = F, CI, Br or mixed. Figure 1.

Sulfenimide fungicides: structural definition

There are c o n s t r a i n t s t o t h i s g e n e r i c f o r m u l a t h a t r e l a t e t o solubility. The i m p l i c a t i o n s o f aqueous s o l u b i l i t y w i l l b e l a t e r discussed. I t must b e l o w . High o i l s o l u b i l i t y , such as would r e s u l t from l o n g c h a i n p o l y h a l o a l k y l groups, w h i l e p r o v i d i n g i n ­ herent f u n g i t o x i c p r o p e r t i e s i s excluded because i t r e s u l t s i n excessive phytotoxicity. R* c a n o n l y r a r e l y e x c e e d two c a r b o n s . F i g u r e 1 a n d t h e b r i e f d i s c u s s i o n now c o n c l u d e d s u m m a r i z e s q u i t e b r i e f l y an e x t r e m e l y voluminous p a t e n t l i t e r a t u r e w i t h c o n t r i b u t i o n s from a l l major c h e m i c a l c e n t e r s o f the w o r l d and c o n t i n u a l l y b e i n g s u p p l e m e n t e d t o t h i s v e r y day. Examples o f t h e s e s u l f e n i m i d e c o m p o s i t i o n s a r e g i v e n i n F i g u r e s 2 a n d 3. A l t h o u g h i t i s n o r m a l l y p r o p e r t o u t i l i z e g e n e r i c names, we w i l l employ t h e u s u a l names b y w h i c h t h e s e compounds a r e b e s t known t h r o u g h o u t t h e w o r l d f o r t h e r e m a i n d e r of t h i s p a p e r . I n t h e s e f i g u r e s we h a v e i n d i c a t e d some m a j o r areas o f u s e f u l n e s s . I n a d d i t i o n t o t h e compounds g i v e n i n t h e f i g u r e s , i t i s n o t an e x a g g e r a t i o n t o s t a t e t h a t w e l l o v e r a t h o u s a n d homologues o f t h i s s e r i e s have been s y n t h e s i z e d . T h i s a u t h o r h a s knowledge o f upwards o f 100 c o m p o s i t i o n s t h a t e x h i b i t s u p e r i o r f u n g i c i d a l properties. As i s u s u a l l y the case, however, s i m p l i c i t y and i n d u s t r i a l a n d a g r i c u l t u r a l e c o n o m i c s d e t e r m i n e w h i c h compounds a c h i e v e b r o a d a g r i c u l t u r a l u s a g e . Of t h o s e s y n t h e s i z e d c a p t a n , P h a l t a n and D i f o l a t a n dominate the market. 1

PESTICIDE CHEMISTRY IN T H E 2 0 T H C E N T U R Y

156

Applications

Structure

CI

Ο

2. Phaltan folpet

Grape Diseases Late Apple Diseases Ornamentals

N-S-C-CI

I CI / C

CI CI

ι ι

v

Broad spectrum Foliar & seed, coffee

/N-S-C-C-H I I CI CI

3. Difolatan captafol

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch009

Broad spectrum Foliar & seed treatments

/N-S-C-CI

1. Captan captan

Ο

4. Euparen dichlofluanid

CI

\

Europe Protective fungicide

S-C-CI I

F

Figure 2.

Some sulfenimide fungicides

Applications

Structure .CH 5. Euparen M tolylfluanid

S

Ο

\

3

CH,

?

S-

Europe Ornamentals fruit

Ç-CI F

I 6. Chlordantoin

CH3-CH2-CH2-CH2-CH2-CH-CH-C

I " Ν -S-C-CI NH-C ' I \> CI n

// 1 / 0

7. Experimental compound

CI

H-C-N-S-OC

I Η

XI

Algicide

\.CI /

8. Experimental compound

Medicinal vaginal infections

\

S0 CH 2

3

??

Protective fungicides

S-C-C-F CI CI

Figure 3.

Some sulfenimide fungicides

N a t u r e o f t h e Ν - S Bond A t t h e t i m e o f t h e d i s c o v e r y o f c a p t a n ( e x c e p t p e r h a p s where s u l f u r was i n a n o x i d i z e d s t a t e ) , v e r y l i t t l e was known a b o u t t h e n a t u r e a n d p r o p e r t i e s o f t h i s bond i n o r g a n i c s t r u c t u r e s . Even t o d a y , c o m p i l a t i o n s o f bond e n e r g i e s o r bond d i s t a n c e s o r s p e c t r o ­ scopic p r o p e r t i e s f a i l t o include data f o r organic chemical

9.

κοΗΝ

The Sulfenimide

157

Fungicides

molecules with the Ν - S - linkage. Nevertheless, t h i s i s the d i s t i n c t i v e a n d d e f i n i t i v e bond f o r t h i s e n t i r e g r o u p o f f u n g i ­ c i d e s , and i t s p r o p e r t i e s b o t h p r o v i d e f o r and l i m i t t h e u s e f u l ­ ness o f these t h e r a p e u t i c agents. I n T a b l e 1 a r e s u m m a r i z e d some values e x t r a c t e d from the l i t e r a t u r e f o r t h e s u b j e c t l i n k a g e . The Ν - S bond e n e r g y was c a l c u l a t e d f r o m t h e P a u l i n g e q u a t i o n b y Dr. P h i l i p Magee ( 1 0 ) . T h e r e i s , f o r e x a m p l e , a n o b v i o u s anomaly i n t h e Raman a n d i n f r a r e d f r e q u e n c i e s (10) (11) (12) ( 1 3 ) .

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch009

\ Table I. The N - S - Bond / Bond Energy

53 Κ cal/Mol

Bond distance

1.686 À

IR absorption

950cm-1

Raman absorption

650 cm-1

The bond s t a b i l i t y i s g r e a t l y m o d i f i e d b y t h e u n u s u a l s u b ­ s t i t u t i o n s on b o t h t h e n i t r o g e n and t h e s u l f u r ( t h e d i c a r b o n y l a t t a c h m e n t t o t h e Ν a n d t h e t r i c h l o r o m e t h y l t o t h e S ) . The e f f e c t o f these electron-withdrawing s u b s t i t u t i o n s c e r t a i n l y a l t e r s t h e bond s t r e n g t h a n d i t s s u s c e p t i b i l i t y t o a t t a c k . These c o n t r i b u t e f u r t h e r t o t h e e x t r a o r d i n a r y c h e m i c a l and b i o l o g i c a l p r o p e r t i e s w h i c h we w i l l s u b s e q u e n t l y examine. Aqueous

Solubility

E a r l y i n t h e h i s t o r y o f p l a n t chemotherapy t h e d i f f e r e n t i a l t o x i c i t y o f t h e t h e r a p e u t i c c h e m i c a l was r e l a t e d t o t h e l i m i t a ­ t i o n o f i t s aqueous s o l u b i l i t y . A c a s e i n p o i n t was t h e 1 9 t h century d i s c o v e r y o f t h e grape f u n g i c i d e , Bordeaux m i x t u r e . S o l u b l e copper s a l t s a r e extremely t o x i c b o t h t o h i g h e r p l a n t s and t o t h e l o w e r g r o u p s s u c h a s a l g a e a s w e l l a s t o t h e f u n g i a n d b a c t e r i a t h a t may a t t a c k them. The a d d i t i o n o f l i m e t o c o p p e r s u l f a t e t o p r e c i p i t a t e a r e l a t i v e l y i n s o l u b l e b a s i c copper s u l f a t e p r o v i d e d among o t h e r p r o p e r t i e s a n aqueous c o n c e n t r a t i o n o f c u p r i c i o n s u f f i c i e n t t o combat t h e f u n g i b u t i n s u f f i c i e n t t o i n t e r f e r e w i t h , except m a r g i n a l l y , the normal metabolic processes of the p l a n t . At Chevron and elsewhere a whole s e r i e s o f copper, z i n c , manganese, c a l c i u m , cadmium, l e a d a n d a r s e n i c s a l t s w e r e m a n u f a c ­ tured as p l a n t p r o t e c t i o n agents and m i c r o n u t r i e n t s by the care­ f u l l y pH c o n t r o l l e d p r e c i p i t a t i o n o f i n s o l u b l e s w h e r e t h e a c t i v e c a t i o n o r anion could only reach a s m a l l , p l a n t - t o l e r a b l e , maxi­ mum c o n c e n t r a t i o n . I n s u c h c a s e s t h i s maximum c o u l d b e c a l c u l a t e d

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch009

158

PESTICIDE

CHEMISTRY

I N T H E 20TH

CENTURY

from t h e a r i t h m e t i c of the s o l u b i l i t y product r e l a t i o n s h i p . Pro­ d u c t s c o n t a i n i n g t h e s e i o n s c o u l d be t e s t e d f o r e f f e c t i v e n e s s a g a i n s t t h e p a t h o g e n and f o r t o l e r a n c e b y t h e h o s t and w o u l d b e d i f f e r e n t f o r each product. One o f t h e h i g h l y s i g n i f i c a n t p r o p e r t i e s o f t h e s u l f e n i m i d e g r o u p and t h e p u r p o s e o f t h i s d i g r e s s i o n r e l a t e s t o t h e l i m i t e d aqueous s o l u b i l i t y o f i t s v a r i o u s members. T a b l e I I p r o v i d e s t h e s o l u b i l i t i e s o f t h r e e a g r i c u l t u r a l l y s i g n i f i c a n t members o f t h i s c l a s s of sulfenimide fungicides. These s o l u b i l i t i e s w e r e q u i t e c a r e f u l l y d e t e r m i n e d (14) and some comment on t h e method employed i s i n s t r u c t i v e . I t was f o u n d e a r l y i n these determinations that i f the time f o r the e s t i m a t i o n o f t h e c o n c e n t r a t i o n o f f u n g i c i d e i n t h e aqueous p h a s e a f t e r s e p a r a t i o n from t h e s o l i d v a r i e d then the values f o r the s o l u ­ b i l i t y a s d e t e r m i n e d b y e x t r a c t i o n a l s o v a r i e d . F u r t h e r , i f one p l o t t e d the time a f t e r s e p a r a t i o n a g a i n s t the assay r e s u l t s , a smooth c u r v e was o b t a i n e d t h a t c o u l d s i m p l y b e e x t r a p o l a t e d t o zero time. This value, of course, i s the e q u i l i b r i u m concentra­ t i o n and i s h i g h e r t h a n any o f t h e e x p e r i m e n t a l v a l u e s a n d i s t h e one q u o t e d i n T a b l e I I . My p u r p o s e i n d e s c r i b i n g t h i s p o r t i o n o f the methodology i s t o p r o v i d e a l o g i c a l t r a n s i t i o n t o t h e h i g h l y s i g n i f i c a n t p r o p e r t y o f t h e s e f u n g i c i d e s , and t h a t i s t h e i r s u s c e p t i b i l i t y to nucleophilic attack.

Table II.

Aqueous Solubility of Captan, Phaltan, a n d Difolatan

FUNGICIDE

Sol. @ 25 deg. C

VA

K

ppm

hrs.

sec.

CAPTAN

3.3

8.2

2.4

PHALTAN

1.25

6.6

2.9

DIFOLATAN

1.4

10.5

d

X10

1.8

I n f a c t t h i s genus o f u s e f u l s u l f e n i m i d e f u n g i c i d e s r e q u i r e s a l o w aqueous s o l u b i l i t y t o p r o t e c t a g a i n s t i t s i n h e r e n t a p p r e ­ ciable hydrolytic i n s t a b i l i t y (14). S u s c e p t i b i l i t y t o N u c l e o p h i l i c D i s p l a c e m e n t and B i o c h e m i c a l Interactions The h a l f - l i f e o f an e q u i l i b r i u m c o n c e n t r a t i o n o f c a p t a n , f o r e x a m p l e , i n d e i o n i z e d w a t e r a t 25 d e g . C i s 8.2 h r s . The maximum c o n c e n t r a t i o n o f 0H~ i s 10"7 m o l e s p e r l i t e r and p r o b a b l y a p p r o a c h e d 10" 9 s i n c e t h e d e t e r m i n a t i o n s were made i n u n b u f f e r e d , d e i o n i z e d w a t e r . The s i g n i f i c a n t p o i n t i s t h a t 0H~ i s a weak t o

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch009

9.

κοΗΝ

The Sulfenimide

Fungicides

159

moderate n u c l e o p h i l e p a r t i c i p a t i n g i n t h e d e s t r u c t i o n o f t h e f u n g i c i d e a t a v e r y l o w c o n c e n t r a t i o n o f i o n and s u b s t r a t e . The author wishes to avoid d i s c u s s i o n as t o the l o c a t i o n of the i n i t i a l attack. P r o b a b l y c a r b o n y l s b u t p o s s i b l y h a l o g e n s may b e i n v o l v e d p r i o r t o t h e u l t i m a t e s c i s s i o n o f t h e N-S bond. Whereas 0H~ i s a r e l a t i v e l y weak n u c l e o p h i l e ( 1 5 ) , b i o l o g i ­ c a l f l u i d s abound w i t h h i g h l y a c t i v e n u c l e o p h i l i c s p e c i e s , p a r t i c u l a r l y s u l f h y d r y l s and s u b s t i t u t e d n i t r o g e n s p e c i e s . This i s i n d e e d r e f l e c t e d i n a s e r i e s o f measurements o n t h e r a t e o f d e g r a d a t i o n o f c a p t a n and o t h e r members o f t h e s u l f e n i m i d e g r o u p i n b l o o d and T a b l e I l l s u m m a r i z e s t h e r a t e s o f t h a t d e g r a d a t i o n i n t h e w h o l e b l o o d o f humans. T h i s r e m a r k a b l e s h o r t l i v e d n e s s ( a n d t h e s p e c i f i c v a l u e s may e r r on b e i n g o n t h e h i g h e r s i d e ) a g a i n j u s t i f i e s f u r t h e r comment. T h e s e measurements w e r e made a t d i f f e r e n t p e r i o d s and w i t h somewhat v a r y i n g c o n c e n t r a t i o n s and techniques. The i m p o r t a n t p o i n t i s n o t t h e a b s o l u t e v a l u e s b u t t h e marked r a p i d i t y o f t h e d e c o m p o s i t i o n ( 1 6 ) ( 1 7 ) ( 1 8 ) . Table III.

Decomposition

of Blood at 2 5 ° C

Fungicide

VA (minutes)

Captan

0.9

Phaltan

0.9

Difolatan

0.8

Certain t o x i c o l o g i c a l i n v e s t i g a t i o n s p a r t i c u l a r l y i n the molecular biology area u t i l i z e the i n t e r a c t i o n of the chemical w i t h s i n g l e c e l l organisms o r the i n j e c t i o n of the chemical i n t o c h i c k eggs o r i s o l a t e d enzyme p r e p a r a t i o n s . These i n v e s t i g a t i o n s p r o v i d e i n t e r e s t i n g and s i g n i f i c a n t i n f o r m a t i o n . A t times such i n f o r m a t i o n has been e x t r a p o l a t e d t o i n d i c a t e h a z a r d a s s o c i a t e d w i t h t h e c h e m i c a l when i n g e s t e d b y man o r h i g h e r mammals f r o m t h e r e s i d u e s r e m a i n i n g o n t h e raw a g r i c u l t u r a l p r o d u c t . The above s u s c e p t i b i l i t y t o n u c l e o p h i l i c a t t a c k and t h e s h o r t ­ l i v e d n e s s o f these f u n g i c i d e s i n b i o l o g i c a l media suggests a low h a z a r d a s s o c i a t e d w i t h t h e i r n o r m a l u s e f o r t h e i n t a c t mammal. I t a c c o u n t s f u r t h e r f o r t h e v e r y l a r g e number o f b i o c h e m i c a l mechanisms t h a t h a v e b e e n i n v o k e d t o e x p l a i n t h e i r t h e r a p e u t i c e f f i c a c y , some o f w h i c h a r e n o t e d i n T a b l e I V ( 1 9 ) ( 2 0 ) ( 2 1 ) ( 2 2 ) (23) ( 2 4 ) .

160

PESTICIDE C H E M I S T R Y IN T H E 2 0 T H

CENTURY

Table IV. Recorded Biochemical Interactions MECHANISMS 1. Inhibition of glyceraldehyde dehydrogenase 2. Alpha chymotrypsin inactivation 3. Oxidative phosphorylation uncoupler 4. Destructive membrane interactions

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch009

5. Destruction of mitochondrial systems

6. Inhibition of oxidation of NADH2 7. Interaction with thiol enzymes 8. Inhibition of chitin biosynthesis

F i e l d Usefulness

and S p e c i f i c i t y

I n T a b l e I I we h a v e shown t h a t t h e two S C C I 3 h o m o l o g u e s , c a p t a n a n d P h a l t a n h a v e c l o s e l y s i m i l a r homogenous r a t e s o f h y d r o l y s i s a l t h o u g h c a p t a n i s a p p r e c i a b l y more s o l u b l e . On t h e o t h e r hand, D i f o l a t a n and P h a l t a n have l o w s o l u b i l i t y b u t t h e rate of h y d r o l y s i s of Phaltan i sapproximately twice that of Difolatan. Not i n the t a b l e s i s t h e f a c t that D i f o l a t a n g e n e r a l l y has two t o f i v e t i m e s t h e i n v i t r o a n t i f u n g a l a c t i v i t y . These d a t a c a n b e c o r r e l a t e d w i t h f i e l d o b s e r v a t i o n . F o r e x a m p l e , i n v i t i c u l t u r e i n C a l i f o r n i a , t h e g r a p e grows and matures i n a g e n e r a l l y d r y and almost i n f e c t i o n - f r e e environment, w h i l e i n N o r t h a n d C e n t r a l E u r o p e and i n much o f t h e M e d i t e r r a ­ n e a n a r e a t h e g r o w i n g a r e a s g i v e r i s e t o endemic i n f e c t i o n s e.g. by P l a s m o p a r a and B o t r y t i s o r g a n i s m s . F u r t h e r , i n these areas, t h e g r a p e s a r e l a r g e l y c u l t i v a t e d f o r w i n e m a k i n g . The y e a s t s that ferment t h e sugars a r e f r e q u e n t l y s e n s i t i v e i n v a r y i n g degree t o s m a l l c o n c e n t r a t i o n s o f f u n g i c i d a l compositions. One w o u l d l i k e t h e n t o h a v e a f u n g i c i d e t h a t p r o t e c t s c l o s e to h a r v e s t b u t where t h e r e s i d u e i s so reduced i n c o n c e n t r a t i o n o r d i s a p p e a r s a l t o g e t h e r a t t h e t i m e o f c r u s h i n g (and s u b s e ­ quently i n the j u i c e ) . R e s i d u e s o f D i f o l a t a n where t h e h y d r o l y s i s r a t e i s low i m p a i r t h e f e r m e n t a t i o n by i n h i b i t i n g t h e growth o f yeasts. P h a l t a n ® a n d / o r c a p t a n s p r a y e d a t t h e same t i m e a s D i f o l a t a n g i v e a l m o s t a s good p l a n t d i s e a s e p r o t e c t i o n , b u t a s t h e c h a r t r e v e a l s , a r e l e s s p e r s i s t e n t . Hence t h e s e a r e u s e d i n much o f E u r o p e f o r c o n t r o l o f g r a p e m i l d e w . F e r m e n t a t i o n pro­ c e e d s a t a p r a c t i c a l r a t e and t h e r e a r e no r e s i d u e s o f t h e p a r e n t f u n g i c i d e i n the wine.

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch009

9.

κοΗΝ

The

Sulfenimide

Fungicides

161

S i m i l a r a n a l y s i s c a n b e made r e g a r d i n g t h e p r o t e c t i o n o f t h e c o f f e e p l a n t and f r u i t . Here the a c t i v i t y o f D i f o l a t a n p l u s i t s r e s i s t a n c e t o h y d r o l y s i s and g r e a t e r p e r s i s t e n c e p r o v i d e s t h e more i d e a l c o m b i n a t i o n o f p r o p e r t i e s . Therefore, under t h e t r o p i c a l , m o i s t c o n d i t i o n s o f Kenya, B r a z i l , C e n t r a l America and South I n d i a , p a r t i c u l a r l y f o r C o l l e t r i c h i u m i n f e c t i o n s , P h a l t a n and c a p t a n a r e m e d i o c r e a n d D i f o l a t a n i s e x c e l l e n t . I n c i d e n t a l l y , none o f t h e s e compounds a r e s y s t e m i c a n d t h e r e s i d u e i s e n t i r e l y on t h e f r u i t , n o t o n t h e b e a n . F i n a l l y , the a p p r e c i a b l e h y d r o l y t i c r a t e o f a l l o f these p r o v i d e f o r t h e a s s u r a n c e t h a t t h e r e w i l l b e no s o i l r e s i d u e s from one season t o the n e x t , a d e c i d e d l y e c o l o g i c a l p l u s . Honesty r e q u i r e s the author t o add t h a t f i e l d t r i a l s and e x p e r i e n c e p r o v i d e d the c h o i c e o f c h e m i c a l both f o r v i t i c u l t u r e and f o r c o f f e e p l a n t p r o t e c t i o n . These p a r a m e t e r s p r o v i d e a r a t i o n a l i z a t i o n f o r t h e p a r t i c u l a r c h o i c e o f compound a n d a r e a n a i d t o the understanding o f that c h o i c e . Organism R e s i s t a n c e

and the S u l f e n i m i d e

Fungicides

There i s a Piedmont farm a r e a i n V i r g i n i a where a p p l e orchards dominate the a g r i c u l t u r a l landscape. C a p t a n has b e e n employed o n many o f t h e s e f a r m s f r o m t h e d a y o f i t s i n t r o d u c t i o n as a p r a c t i c a l f u n g i c i d e t o t h e p r e s e n t . The s p r a y s c h e d u l e s c a n r e q u i r e a s many a s 15 t o 20 a p p l i c a t i o n s d u r i n g t h e g r o w i n g s e a s o n , y e t t h e same d o s a g e i s employed t o d a y a s when t h e c h e m i ­ c a l was f i r s t u t i l i z e d . I t was c u s t o m a r y t o a s k o u r p l a n t p a t h ­ o l o g i s t s o v e r the y e a r s i f , f i r s t , any e v i d e n c e o f f i e l d o r g a n i s m r e s i s t a n c e was o b s e r v e d , a n d s e c o n d , i f n o t , why n o t . The answer t o t h e f i r s t q u e s t i o n i s i n f a c t n e g a t i v e . The a n s w e r s t o t h e s e c o n d w e r e many, d i f f e r e n t , v a r i e d , a n d some­ times c o n t r a d i c t o r y . I n the s e c t i o n o f t h i s paper t h a t f o l l o w s , we w i l l e x p l o r e t h i s m a t t e r o f p r a c t i c a l r e s i s t a n c e t o f u n g i c i d e s . I t i s now commonplace t o r e c o g n i z e t h a t r e s i s t a n c e t o chemot h e r a p e u t i c a g e n t s i s a n o r m a l a n d e x p e c t e d phenomenon a n d t h a t the nonappearance o f r e s i s t a n c e i s the abnormal. I f one r e r e a d s the J o u r n a l o f Economic Entomology o f the e a r l y 5 0 s and 60's, one i s s t r u c k b y a s e e m i n g d i s r e g a r d , o r , a t l e a s t , l a c k o f a p p r e c i a t i o n and r e c o g n i t i o n o f t h i s fundamental law o f b i o l o g y and, i n c i d e n t a l l y , o f c h e m i s t r y (Le C h a t e l i e r ' s P r i n c i p l e ) . T h e r e w e r e , o f c o u r s e , some e x c e p t i o n a l s c i e n t i s t s " c r y i n g i n the w i l d e r n e s s b u t t h e y w e r e v e r y much t h e m i n o r i t y . Now t h a t f l i e s i n Denmark's d a i r i e s a r e r e s i s t a n t t o a l l i n s e c t i c i d e s , that l i k e w i s e are c e r t a i n t i c k s i n A u s t r a l i a , that H e l i o t h i s s p e c i e s o f v a r i o u s t y p e s i n t h e U.S., the Near E a s t and elsewhere e x h i b i t m u l t i p l e r e s i s t a n c e , t h a t the Gonococcus i n t h e U.S. h a s shown r e s i s t a n c e t o a s e r i e s o f s u l f a d r u g s , t o v a r i o u s p e n i c i l l i n h o m o l o g u e s , a n d even now t o t h e t e t r a c y c l i n e s , t h a t c e r t a i n members o f t h e A c a r i d a e h a v e s u c c e s s f u l l y a d a p t e d t o three o r four d i f f e r e n t classes of chemical therapeutic agents, f

1 1

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch009

162

PESTICIDE C H E M I S T R Y IN T H E 2 0 T H

CENTURY

t h a t many f u n g a l o r g a n i s m s m a n i f e s t r e s i s t a n c e t o c e r t a i n f u n g i ­ c i d e s , e t c . , e t c . , we r e c o g n i z e , a c c e p t a n d e x p e c t t h i s f u n d a ­ mental p r o p e r t y o f l i v i n g organisms t o adapt t o u n f a v o u r a b l e environmental pressures — to whit, foreign chemicals. In f a c t t h i s fundamental law o f l i f e guarantees t h a t t h e r e w i l l b e a b i c e n t e n n i a l ACS m e e t i n g i n t h e y e a r 2076, a n d t h a t c h e m i s t s , i n d e e d , h a v e a l o n g and n e v e r t o t a l l y s u c c e s s f u l f u t u r e . I n t h e n e x t f e w p a r a g r a p h s we w i l l b r i e f l y s u m m a r i z e some recent experiences r e l a t i n g to p r a c t i c a l resistance to fungi­ cides . Ten t o f i f t e e n y e a r s ago t h e two s u r f a c t a n t - t y p e f u n g i c i d e s i n F i g u r e 4, w e r e c o n s i d e r e d among t h e most e f f e c t i v e a g e n t s a g a i n s t V e n t u r i a inaequaUs and c e r t a i n o t h e r organisms. Where these substances were used i n t e n s i v e l y , o b s e r v a t i o n s o f t h e need f o r i n c r e a s e d d o s a g e w e r e made, a n d t o d a y t h e s e f u n g i c i d e s h a v e a d e c l i n i n g r o l e i n American a g r i c u l t u r e .

ΒΧ

ΪΤ

dodine

Use

Structure

Name

ΓΗ Ν Γ

n-C 2n25~ "" N

1

c

Θ

Π O - CΛΗ -CH3

VE

H N H h0 1

Glyodin

TURIA

inaequalis

1

O-C-CH3

~Cl735

n

*

H

Apple scab Cherry leaf spot

H© H, Alteration of membrane permeability Moderate resistance and local systemic. Figure 4.

Surfactant fungicides

1

The c o n c e p t o f p l a n t ' i m m u n i t y t o a t t a c k i n g o r g a n i s m s seem­ ed a n d i s a n a t t r a c t i v e h y p o t h e s i s . The i n t r o d u c t i o n o f s y s t e m i c f u n g i c i d e s p r o v i d e d a s o r t o f p r a c t i c a l a p p r o a c h t o 'immunity' and was r e g a r d e d a s t h e s o l u t i o n t o t h e p r o b l e m s o f p l a n t chemo­ therapy. I n d e e d , s y s t e r n i e s a r e most v a l u a b l e a n d u s e f u l a g e n t s . They a r e n o t p a n a c e a s . They h a v e l i m i t a t i o n s . The s t r u c t u r e s o f some o f t h e more u s e f u l s y s t e m i c s o f t h e B e n z i m i d a z o l e g r o u p a r e p r o v i d e d f o r r e f e r e n c e i n F i g u r e 5.

9.

κοΗΝ

The Sulfenimide

Fungicides

Name

163

Structure

Benomyl

Use

C-NH-C-OCH

Thiopha nates NF44 Many Others

3

NH-C-NH-C-0R NH-C-NH-C-OR

Mildews Fairly broad scope

Same

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch009

ι \ MBC

H

Ο Figure 5.

I X

s

0 C-NH-C^OCH, J

... J metabolite I

Benzimidazole systemics

Another group o f h e t e r o c y c l e s has y i e l d e d v a l u a b l e a n t i ­ fungal agents outstanding against c e r t a i n i n f e c t i o n s o f g r a i n . I n Greece ( 2 5 ) , C e r c o s p o r a i n f e c t i o n s o f sugar b e e t s were t r e a t ­ ed f o r two y e a r s w i t h B e n o m y l . The f i r s t r e s p o n s e was s u p e r b , but r e p e a t e d a p p l i c a t i o n s r e v e a l e d an i n c r e a s i n g r e s i s t a n c e and i t was r e p l a c e d a f t e r two y e a r s b y a s e c o n d s y s t e m i c , Vitavax ( F i g u r e 6 ) . The same s e q u e n c e o c c u r r e d a n d r e p o r t s h a v e b e e n made t h a t G r e e k a g r i c u l t u r i s t s h a v e h a d t o r e t u r n t o a more c o n ­ v e n t i o n a l , a l b e i t , a more t o x i c p r o t e c t i v e f u n g i c i d e , B r e s t a n (Figure 7 ) . Name

Structure

Use

;ra spp.

Figure 6.

Other systems

PESTICIDE C H E M I S T R Y I N T H E 2 0 T H C E N T U R Y

164

Use Cercospora Sugar Beets Potatoes

Same

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch009

Duter

Figure 7.

Organotin fungicides

I n J a p a n , a w h o l e new g e n e r a t i o n o f a n t i f u n g a l a g e n t s d e r i v e d from fermentation processes provided great promise. I n T a b l e V, we r e c o r d t h e e x p e r i e n c e o f p a t h o l o g i s t s i n J a p a n , who have noted r e s i s t a n c e i n l a b o r a t o r y , greenhouse and f i e l d i n a r e l a t i v e l y short period t o s t r u c t u r a l l y quite d i s s i m i l a r a n t i ­ b i o t i c fungicides. Against theattack o f Alternaria kikuchiana p a r t i c u l a r l y on p e a r s , Japanese o r c h a r d i s t s have r e t u r n e d t o a member o f t h i s s u l f e n i m i d e g r o u p , D i f o l a t a n ( 2 6 ) .

Table V .

Resistance to Antibiotics

Antibiotic

Where Noted

Major Organism

Blasticidin S

Lab and Greenhouse

Pyricularia oryzae

Kasugamycin

Field (L and G)

Pyricularia oryzae

Polyoxins

Field (L and G)

Alternaria kikuchiana

T. Misato and K. Ko, 3rd Proceedings, IUPAC Conf. - Pesticides Helsinki, August 1974

P a r t i c u l a r i t i e s and Features Protection Fungicides

o f Organism R e s i s t a n c e

to Plant

T h i s abnormal non-appearance o f p r a c t i c a l r e s i s t a n c e o f f u n g a l organisms t o t h e s u l f e n i m i d e group m e r i t s e x p l o r a t i o n . T h i s we s h a l l do b y e x a m i n i n g some c u r r e n t e x p l a n a t i o n s b y

9.

κοΗΝ

The

Sulfenimide

Fungicides

165

g e n e r a l i z i n g from the e x p e r i e n c e o f r e s i s t a n c e and the p r o p e r t i e s of the c h e m i c a l a g e n t s , and q u i t e unashamedly by s p e c u l a t i o n . I n a r e c e n t book d e v o t e d t o b i o c h e m i c a l mechanism o f p e s t i c i d a l a c t i o n , the author s t a t e s (quoting primary sources) that r e s i s t a n c e t o systemics i s caused by "the h i g h s e l e c t i o n pressure e x e r t e d by these f u n g i c i d e s on the f u n g a l p o p u l a t i o n w i t h t h e r e s u l t t h a t , i n some c i r c u m s t a n c e s o n l y , r e s i s t a n t s t r a i n s s u r ­ vive. O l d e r f u n g i c i d e s seem t o h a v e b e e n l e s s e f f e c t i v e a s f u n g i c i d e s t h a n t h e new compounds"(27)This means t h a t most o f t h e chemical p r o t e c t a n t s such as the s u l f e n i m i d e s l e f t b o t h r e s i s t a n t and s e n s i t i v e s t r a i n s a n d p r e s u m a b l y , a n d a s i s u s u a l , t h e s e n s i t i v e p o p u l a t i o n adapts b e t t e r t o the t o t a l environment. I t i s p o s s i b l e t h a t w i t h s y s t e m i c s b e c a u s e t h e y h a v e a more s p e c i f i c mode o f a c t i o n t h a n most o f t h e o l d e r compounds,... t h e r e may b e l e s s c h a n c e o f t h e i r u n d e r g o i n g a m u l t i p l i c i t y o f nonl e t h a l r e a c t i o n s w i t h i n the fungal c e l l " (27). This i m p l i e s an ease o f d e t o x i f i c a t i o n o f the c l a s s i c a l p r o t e c t a n t s which p e r ­ mitted a larger population of survivors. There are f u r t h e r g e n e r a l i z a t i o n s t h a t should be s t r e s s e d . The f i r s t o f t h e s e a l s o r e l a t e s s y s t e m i c a c t i v i t y t o s p e c i f i c i t y o f b i o c h e m i c a l mechanism. An e f f e c t i v e f u n g i t o x i c s y s t e m i c must n o t r e a c t a n d b e d e t o x i f i e d o r i n t e r f e r e w i t h p l a n t enzymes. Were t h i s n o t t h e c a s e , e i t h e r a p h y t o t o x i c e f f e c t w o u l d r e s u l t (as f o r 2,4-D) o r a n i n e f f e c t i v e f u n g i c i d e w o u l d r e s u l t . Exactly t h e s e e f f e c t s a r e a c h i e v e d when t h r o u g h s y n t h e s i s t h e s o l u b i l i t y of the s u l f e n i m i d e s i s i n c r e a s e d . This author has, a l a s , q u i t e f r e q u e n t l y c o n v e r t e d good f u n g i c i d e s i n t o m e d i o c r e h e r b i c i d e s b y such s y n t h e t i c e f f o r t on the s o l u b i l i t y m o d i f i c a t i o n s o f t h e s u l f e n i m i d e g e n e r i c s t r u c t u r e . A s y s t e m i c must t h e n b e p r e f e r ­ a b l y a c h e m i c a l l y r e l a t i v e l y s t a b l e substance and not a h i g h l y reactive nucleophile o r electrophile. A f u r t h e r i m p l i c a t i o n o f t h i s r e l a t e s t o o n e way i n w h i c h r e s i s t a n c e may b e a c q u i r e d . A s i n g l e s i t e chemical creates a l e s i o n i n some h i g h l y e s s e n t i a l b i o c h e m i c a l pathway. Organisms can however c r e a t e a s h u n t where t h e y c a n a c c o m p l i s h t h e i r m e t a b o l i s m b y a l t e r i n g t h a t pathway. T h i s may b e p o s s i b l e f o r a s i n g l e s i t e t o x i c a n t . I t i s m a t h e m a t i c a l l y most u n l i k e l y f o r the m u l t i s i t e chemicals. They p r e s u m a b l y may b e l e t h a l b y r e a c t i n g w i t h a number o f v i t a l enzyme s y s t e m s . In fact, i t i s v e r y d i f f i c u l t w i t h a m u l t i s i t e c h e m i c a l t o be e n t i r e l y c e r t a i n as t o i t s mode o f a c t i o n . The e x p e r i m e n t a l p r o c e d u r e may p r e ­ determine the c o n c l u s i o n (Table I V ) . A s o r t o f b i o c h e m i c a l 'uncertainty p r i n c i p l e i s here involved. I t i s possible that d i f f e r e n t f u n g i are k i l l e d by d i f f e r e n t biochemical i n t e r ­ a c t i o n s by t h e s e m u l t i s i t e t o x i c a n t s . A g a i n the m a t h e m a t i c a l p r o b a b i l i t y f o r r e s i s t a n c e i s reduced. Further, these p l a n t f u n g u s - c h e m i c a l i n t e r r e l a t i o n s h i p s enable us t o p a r t i c u l a r i s e i n a manner t h a t d i f f e r e n t i a t e s o u r e x p e r i e n c e a n d c o n c l u s i o n s from t h a t o f the i n s e c t i c i d e f i e l d .

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch009

l f

f

1

1

166

PESTICIDE C H E M I S T R Y IN T H E 2 0 T H C E N T U R Y

The g e n e r a l i z a t i o n s , t h e n , i n F i g u r e 8 r e f e r e x c l u s i v e l y t o t h e s u b j e c t m a t t e r a t hand. Single s i t e substances, with a p p r e c i a b l e aqueous s o l u b i l i t y , w h i c h a r e t r a n s l o c a t a b l e , w i l l for the reasons mentioned w i t h h i g h p r o b a b i l i t y develop r e s i s t ­ ance i n t h e organisms w h i c h a r e t h e i r t a r g e t s . M u l t i s i t e chemi­ c a l s , n o n w a t e r s o l u b l e a n d n o n s y s t e m i c , show i f n o t no t e n d e n c y , at l e a s t a h i g h l y reduced p r o b a b i l i t y f o r the i n d u c t i o n o f resistance. Activity Spectrum

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch009

Fungicides Benzimidazoles (Benomyl, thiophanates etc.)

++

Oxathiins (Vitavax)

Biochem Translocation Sites (Aq.Solubility) —

Resistance

+++

++

+

+++

+

Antibiotics (Polyoxin etc.)

+

+++

++

Surfactant type (glyodin, cyprex)

+

—

+

+

Dithiocarbamates (maneb,thiram etc.)

+++

++

—

Sulfenimides (captan, Difolatan)

+++

+++

Tentative & Arbitrary Values vary between + + + for highest to Figure 8.

for absent or lowest.

Resistance and properties of fungicidal groups

I n a n a r t i c l e o n t h e B i o c h e m i c a l Mode o f A c t i o n o f F u n g i c i d e s (28) t h e a u t h o r s g e n e r a l i z e d on f u n g i c i d a l r e s i s t a n c e o n t h e b a s i s o f w h e t h e r t h e i r b i o c h e m i c a l mode o f a c t i o n i n v o l v e d e l e c t r o n transport and fundamental energetics o r i n v o l v e d i n t e r f e r e n c e w i t h m e t a b o l i c changes. Our p o i n t o f v i e w d i f f e r s somewhat, e m p h a s i z i n g o r g a n i c c h e m i c a l r e a c t i v i t y a n d a v o i d i n g s p e c i f i c b i o c h e m i c a l mechanism w h i c h i s s o m e t i m e s c l o u d e d b y d o u b t a n d some c o n t r o v e r s y . O b v i o u s l y , one c a n n o t p r e c i s e l y q u a n t i f y t h e e l e m e n t s o f F i g u r e 8. I t i s n e v e r t h e l e s s h i g h l y i n d i c a t i v e . R e s i s t a n c e o f a p r a c t i c a l nature i s r a r e l y , i f ever, encountered i n normal f i e l d p r a c t i c e by t h e s u l f e n i m i d e s ( o r f o r example, t h e d i t h i o ­ c a r b a m a t e s , F i g u r e 9) - i n s o l u b l e , m u l t i s i t e p r o t e c t i v e s . T h e water s o l u b l e s i n g l e s i t e and v a r i a b l y t r a n s l o c a t a b l e a n t i ­ b i o t i c s , benzimidazoles, oxathiins, etc., etc., a l l exhibit degrees o f f i e l d r e s i s t a n c e . As f a r a s t h i s a u t h o r knows, t h i s a n a l y s i s can be extended over t h e whole c l a s s o f p l a n t p r o t e c t i o n fungicides.

9.

κοΗΝ

The Sulfenimide

Fungicides

Name

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch009

Broad scope fungicides.

N-C

Nabam Zineb Maneb

TMTD

Uses

Structure

Ziram Vapam Ferbam

Thiram

167

iPsO-C-NH - C H C H N H - C - S @ £ > r

(m = 2)

Limited foliage and seed treatment.

;N-C-(S) -C-N / 11

m

CH

3

f ^ J ^ '

r

CH Various Linear and Cyclical 3

-N-C-S-Homologues Figure 9.

Dithiocarbamate fungicides

Summary I n summary, we h a v e a t t e m p t e d t o c o v e r b r i e f l y ( T a b l e V I ) the h i s t o r y o f t h e development o f t h i s group o f f u n g i c i d e s . The s u l f e n i m i d e s a r e a b r o a d genus p r o v i d i n g o p p o r t u n i t i e s f o r much s y n t h e t i c m o d i f i c a t i o n . The compounds p r e s e n t l y e x p l o i t e d , p a r t i c u l a r l y c a p t a n , P h a l t a n and D i f o l a t a n , a r e c h a r a c t e r i z e d b y the r e l a t i v e s i m p l i c i t y o f t h e i r s t r u c t u r e s .

Table V I .

T h e Sulfenimide Fungicides Outline

1. Introduction

a) Brief History b) Chemical Definition c) Examples

2. On the nature of the = Ν - S -

bond

3. Aqueous solubility of useful compounds 4. Susceptibility to Neucleophilic Displacement a) Hydrolytic Instability b) Instability in Biological Media 5. Attributed Biochemical Mechanisms 6. Correlations between chemical properties and field efficacy - Examples 7. Organism Resistance and the Sulfenimides.

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168

PESTICIDE C H E M I S T R Y IN T H E 2 0 T H C E N T U R Y

The p a r t i c u l a r f e a t u r e t h a t d e f i n e s t h e c l a s s , a n d c o n t r i b ­ u t e s t o u s e f u l c h a r a c t e r i s t i c s and t o l i m i t a t i o n s i s the Ν - S bonds, a l i n k a g e which w i t h i n t h e c o n s t r a i n t s o f t h e g e n e r i c formula i s p a r t i c u l a r l y susceptible to n u c l e o p h i l i c attack. This r e q u i r e s t h a t u s e f u l members o f t h e c l a s s p o s s e s s l o w s o l u b i l i t y , p a r t i c u l a r l y a q u e o u s , s o t h a t h y d r o l y t i c d e s t r u c t i o n may b e m a i n ­ tained a t a low p r a c t i c a l l i m i t . We h a v e c o r r e l a t e d f i e l d u s e ­ f u l n e s s o f members o f t h i s c l a s s t o t h e i r c h e m i c a l and p h y s i c a l p r o p e r t i e s as above d i s c u s s e d . Many b i o c h e m i c a l i n t e r a c t i o n s o f t h e s u l f e n i m i d e s w i t h enzyme s y s t e m s a n d b i o l o g i c a l s t r u c t u r e s h a v e b e e n d e s c r i b e d i n t h e l i t e r a t u r e a n d c a n b e amply d e m o n s t r a t e d w i t h i s o l a t e d s y s t e m s . A t t h i s s t a g e , we must c o n c l u d e t h a t t h e s u l f e n i m i d e s a r e i n v o l v e d i n b i o c h e m i c a l m u l t i s i t e a t t a c k , most l i k e l y w i t h t h e s u l f h y d r y l a s s o c i a t e d enzymes a n d co-enzyme s y s t e m s . F i n a l l y , we h a v e s u r v e y e d p a r t i c u l a r i t i e s t h a t p e r t a i n t o the f u n g i c i d e r e s i s t a n c e f i e l d . From t h i s s u r v e y we h a v e p r e ­ s e n t e d some g e n e r a l i z a t i o n s . These a l l p o i n t t o t h e l o w p r o b ­ a b i l i t y o f organism r e s i s t a n c e i n the f u t u r e t o these sulfenimide f u n g i c i d e s and t o f u n g i c i d e s t h a t p o s s e s s s i m i l a r p h y s i c a l and biochemical c h a r a c t e r i s t i c s . In contrast t o t h e p r o b l e m s o f f i e l d e n t o m o l o g y , one c a n f e e l o p t i m i s t i c a b o u t t h e p r e s e n t s t a t u s and t h e f u t u r e f o r p l a n t d i s e a s e c h e m o t h e r a p e u t a n t s . We h a v e t h e o p p o r t u n i t y f o r r e a s o n ­ a b l e p e s t management a n d w i t h p r o p e r p r e c a u t i o n s , c a n a v o i d g r o s s m a n i f e s t a t i o n s o f p r a c t i c a l fungus r e s i s t a n c e . This includes the a v o i d a n c e o f e x c e s s i v e dependence o n t h e s y s t e r n i e s a n d t h e j o i n t employment i n a f e l i c i t o u s manner o f p r o t e c t a n t s a n d s y s t e m i c s . I n the mid 1 9 7 0 s , t h e avoidance o f r e s i s t a n c e i s a s o c i a l r e s p o n s i b i l i t y i n v o l v i n g a l l o f us, i n government, i n e d u c a t i o n , i n i n d u s t r y and i n a g r i c u l t u r e . From t h e p a r t i c u l a r i t i e s above o u t l i n e d , we know w h i c h chemicals can be u t i l i z e d w i t h minimal p r o b a b i l i t i e s o f r e s i s t ­ a n c e d e v e l o p m e n t . Among t h e s e c o m p o s i t i o n s a r e t h e s u b j e c t f u n g i c i d e s o f t h i s paper - t h e s u l f e n i m i d e s . f

Literature Cited 1. K i t t l e s o n , A.R., Science (1952), 115, 84. 2. K i t t l e s o n , A. R., J. Agr. Food Chem. (1953), 1, 677. 3. K i t t l e s o n , A. R., U.S.P. 2,553,770-2,553,778. 4. Loc. cit. (2) above gives a description of Dr. Daines' technique and his demonstration of s i g n i f i c a n t a n t i ­ fungal a c t i v i t y . 5. Daines, R. Η., Plant Disease Reporter (1956), 40, 335. 6. Daines, R. Η., Plant Disease Reporter (1955), 39, 739. 7. Van der K i r k , G. J. Μ., Abstract of Proc. Third Int. Conf. of Pest. Chem., H e l s i n k i (1974) Abstract M 182. 8. Kohn, G. Κ., U.S.P. 3,178,447. 9. U.S.P. 2,533,773.

9.

KOΗΝ

10. 11. 12. 13. 14. 15. 16.

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch009

17., 18.

19. 20. 21. 22. 23. 24. 25. 26. 27.

28.

The Sulfenimide Fungicides

169

Calculations by Dr. P h i l i p Magee, Res. Dept., Chev. Chem. Co. By the same method, values for related bonds are N-O = 38, N-Cl = 42, Cl-Cl = 57 (K c a l ) . Torok, F . , et al, Acta Chim (Budapest) (1970), 63(4), 417. H a r g i t t a i , I., et al, Magy Kem. Foly (1970), 76(2), 63. Goehring, Μ., Chem. Ber. (1947), 80, 219. A b e l l , J., The Water S o l u b i l i t y of Difolatan, Captan and Phaltan, Unpublished - Internal Co. File, Chev. Chem. Co. dated January 5, 1968. Streitweiser, Α., Chem. Reviews (1956), 56, 571. Crossley, J., The S t a b i l i t y of Captan i n Blood and s i m i l a r studies. Unpublished Chev. Chem. Co. F i l e s . Very recent studies r e f l e c t on the ease of formation and s t a b i l i t y c h a r a c t e r i s t i c s of the free r a d i c a l N-S derived from model compounds. Whether such a r a d i c a l species i s involved i n the biochemistry of the sulfenimides i s not known. See: Pannen, W. C., Newkirk, D. O., J.A.C.S., (1976), 98, 516. M a i l l a r d , R. Α., Ingold, K. U., J.A.C.S. (1976), 98, 520. Lukens, R. J., Phytopathology (1962), 52, 740. Siegel, M. R., Pest. Biochem. P h y s i o l . (1971), 1, 225. Siegel, M.R., Pest. Biochem. P h y s i o l . (1971), 1, 234. Nelson, B. D . , Biochem. Pharmacol. (1971), 20, 749. Nelson, B. D . , Biochem. Pharmacol. (1971), 20, 737. Marks, E. P . , Sowa, Β. Α., Personal Communications, to be published. Georgopoulos, S. G . , The Third Inter. Cong. of Pest. Chem. H e l s i n k i (1974). Misato, T., Ko, Κ., The Third Inter. Cong. of Pest. Chem. H e l s i n k i (1974) and Personal Communications. C o r b e t t , J. R., The Biochemical Mode of Action of Pesti­ cides. Academic Press, London and New York (1974) pp. 230231; discussion of Evans, Ε . , Pest Science (1971), 2, 192. S i j p e r s t e i j n , Κ., Van der K i r k , G. J. Μ., Proc. 5th Br. Insect, and Fung. Conf. Brighton (1969). V o l . 3, pp. 724 et. seq.

10 The Development of Agricultural Antibiotics TOMOMASA MISATO

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch010

The Institute of Physical and Chemical Research, Wako-shi, Saitama 351, Japan

Introduction The successful use of a n t i b i o t i c s against b a c t e r i a l diseases of human beings has led to a large scale screening of a n t i b i o t i c s effect for plant disease control in the world. Many a n t i b i o t i c s developed for medical purposes were investigated for a c t i v i t y against plant pathogens. Furthermore screening of soil organisms for production of a n t i b i o t i c substances was started with the prime purpose of plant disease c o n t r o l . However, the results obtained with a n t i b i o t i c s and a n t i b i o t i c containing culture broth did not fulfil the high expectations. Many of them were too unstable under field conditions or showed toxic side effects on plants. Most a n t i b i o t i c s were rather expensive, even when used as a crude product. In western countries only a few a n t i b i o t i c s have been developed for p r a c t i c a l use. These are streptomycin, tetra­ cycline, cycloheximide and g r i s e o f u l v i n . Streptomycin, the first a n t i b i o t i c introduced in a g r i c u l t u r e , was used in the United States for the control of pear f i r e b l i g h t . This a n t i b i o t i c and a mixture of streptomycin and tetracycline have been used for the control of b a c t e r i a l plant diseases, while cycloheximide and griseofulvin have been used for the control of fungal plant diseases. Cycloheximide is a very powerful fungicide, but unfor­ tunately, highly toxic to plants, which r e s t r i c t s its use against plant diseases. Griseofulvin i s a much less phytotoxic systemic fungicide, but its use is also restricted, because the r e l a t i o n of its manufacturing cost to its performance under field condition is not quite satisfactory. In Japan, these four a n t i b i o t i c s had been used only on a very l i m i t e d scale for p r a c t i c a l control of plant diseases, u n t i l the curative effect of blasticidin S on r i c e blast was discovered by the author's research group i n 1958. The successful application of blasticidin S against r i c e blast has stimulated the development of a g r i c u l t u r a l a n t i b i o t i c s and led to the discovery of several excellent a n t i b i o t i c s , such as kasuga­ mycin, polyoxins and validamycin etc. Nowadays, blasticidin S and kasugamycin have been in p r a c t i c a l use for r i c e blast control instead of mercuric fungicides, and polyoxins and validamycin have ;

170

1974

1968

1964

1964

1957

1972

1970

1967

1965

1961

1959

1959

Registration

Insecticidal Antibiotics Tetranactin

ANTIBACTERIAL ANTIBIOTICS Streptomycin (Wettable Powder) Cellocidin (Wettable Powder) Chloramphenicol +Basic copper (Wettable Powder) Novobiocin (Solution)

ANTIFUNGAL ANTIBIOTICS Cycloheximide (Wettable Powder) Griseofulvin (Paste) Blasticidin S (Dust) (Wettable Powder) (Solution) Kasugamycin (Dust) (Wettable Powder) (Solution) Polyoxins (Dust) (Wettable Powder) (Solution) Ezomycin (Wettable Powder) Validamycin (Dust) (Wettable Powder)

Antibiotics

Blight

Insects Carmine Mite of F r u i t s and Tea

B a c t e r i a l Canker of Tomatoes

B a c t e r i a l Diseases of F r u i t s and Vegetables Rice B a c t e r i a l Leaf B l i g h t Rice B a c t e r i a l Leaf B l i g h t

Rice Sheath

Stem Rot of Kidney Bean

Rice Sheath B l i g h t Fungal Diseases of F r u i t s and Vegetables

Rice Blast

Rice B l a s t

Onion Downy Mildew Shoot B l i g h t of Japanese Larch Fusarium W i l t of Melon

Diseases

0

10

0

349

3,893 94

0

387 418 34

7,930 265 10

1,250 3 152

2

17

(ton)

(10

0

33,130

0

692,086

513,876 143,256

0

32,121 960,982 38,216

507,762 221,805 8,820

75,000 2,547 102,426

4,700

3

(1974)

35,020

Amounts used i n Japan

Table I . A g r i c u l t u r a l A n t i b i o t i c s used i n Japan

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch010

yen)

PESTICIDE C H E M I S T R Y

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch010

172

IN T H E 2 0 T H

CENTURY

been used t o c o n t r o l t h e s h e a t h b l i g h t o f r i c e p l a n t i n s t e a d o f arsenic fungicides. The amount o f a n t i b i o t i c s u s e d i n J a p a n i s shown i n T a b l e I . The d e v e l o p m e n t o f a g r i c u l t u r a l a n t i b i o t i c s has n o t b e e n l i m i t e d o n l y f o r c o n t r o l l i n g p l a n t d i s e a s e s , b u t h a s e x t e n d e d w i d e r and more a c t i v e l y o v e r v a r i o u s a r e a s s u c h a s u t i l i z a t i o n o f i n s e c t i c i d e s , h e r b i c i d e s and p l a n t r e g u l a t o r s i n J a p a n . As shown i n T a b l e I I , many compounds o f m i c r o b i o l o g i c a l o r i g i n a r e a l r e a d y u s e d as p e s t i c i d e s o r show p r o m i s e f o r practical application. B l a s t i c i d i n S; e t c . as a n t i f u n g a l a n t i ­ b i o t i c s , s t r e p t o m y c i n , e t c . as a n t i b a c t e r i a l a n t i b i o t i c s , t e t r a n a c t i n as a m i t i c i d e , and g i b b e r e l l i n s as p l a n t g r o w t h r e ­ g u l a t o r s a r e p r a c t i c a l l y u s e d . A a b o m y c i n as an a n t i v i r a l a n t i ­ b i o t i c , a p r o d u c t o f B a c i l l u s t h u r i n g e n s i s as a i n s e c t i c i d a l a n t i ­ b i o t i c and a n i s o m y c i n d e r i v a t i v e s as h e r b i c i d e s h a v e b e e n t e s t e d f o r p r a c t i c a l use i n the f i e l d s . Table I I .

Pesticidal

compounds o f m i c r o b i o l o g i c a l

[Fungicide] * Antifungal antibiotics * Antibacterial antibiotics Antiviral antibiotics [insecticide] * Miticidal antibiotic * Bacterial toxin [Herbicide] Herbicidal antibiotic [Growth r e g u l a t o r ] * Fungal product

: : :

B l a s t i c i d i n S, e t c . Streptomycin, e t c . Aabomycin, e t c .

:

Tetranactin

:

Bacillus

:

Anisomycin

: *

origin

thuringensis

Gibberellins

P r a c t i c a l l y u s e d as p e s t i c i d e s

R e v i e w s on many a n t i b i o t i c s i n c l u d i n g c y c l o h e x i m i d e , g r i s e o f u l v i n and s t r e p t o m y c i n t e s t e d f o r t h e p u r p o s e o f a g r i c u l ­ t u r a l use i n w e s t e r n c o u n t r i e s have been p u b l i s h e d ( 1 - 6 ) . I ti s the purpose o f t h i s paper t o d i s c u s s t h e p r e s e n t s t a t u s o f a n t i ­ b i o t i c s a s p l a n t d i s e a s e c o n t r o l a g e n t s . The d i s c u s s i o n w i l l m a i n l y be l i m i t e d t o a n t i b i o t i c s w h i c h a r e p r a c t i c a l l y u s e d a s new p e s t i c i d e s i n J a p a n . F o r t h e o t h e r l i t e r a t u r e , t h e r e a d e r may r e f e r t h e r e v i e w s m e n t i o n e d above. Antifungal

antibiotics

B l a s t i c i d i n S. B l a s t i c i d i n S i s t h e f i r s t s u c c e s s f u l a g r i ­ c u l t u r a l a n t i b i o t i c developed i n Japan. I t was i s o l a t e d f r o m t h e c u l t u r e f i l t r a t e s o f Streptomyces griseochromogenes by T a k e u c h i e t a l . ( 7 ) , and t h e p o t e n t c u r a t i v e e f f e c t o f b l a s t i c i d i n S on r i c e b l a s t was f o u n d b y M i s a t o elt a l . ( 8 ) . T h e r e a f t e r t h e b e n z y l aminobenzene s u l f o n a t e o f b l a s t i c i d i n S was r e p o r t e d t o be l e a s t phytotoxic to the host plant without reducing antifungal a c t i v i t y a g a i n s t P y r i c u l a r i a o r y z a e , t h e p a t h o g e n o f r i c e b l a s t ( 9 ) , and

MisATO

10.

Agricultural

173

Antibiotics

t h i s s a l t has been i n d u s t r i a l l y produced f o r a g r i c u l t u r a l use. 1) C h e m i s t r y a n d mode o f a c t i o n : The c h e m i c a l s t r u c t u r e o f b l a s t i c i d i n S has been s t u d i e d e x t e n s i v e l y by Yonehara and h i s c o - w o r k e r s a n d t h e f i n a l s t r u c t u r e a s s i g n e d b l a s t i c i d i n S i s 1(l -cytosinyl)-4-[L-3 -amino-5 -(l -N-methylguandidino)-valerylamino]-!,2,3,4-tetradeoxy-B-D-erythro-hex-2-eneuronic a c i d as shown i n F i g u r e 1 ( 1 0 , 1 1 ) . S e t o e t a l . (12,13) s t u d i e d t h e b i o ­ s y n t h e s i s o f b l a s t i c i d i n S by the p r o d u c i n g organism u s i n g Relabeled suspected precursors. The r e s u l t s o b t a i n e d w e r e t h a t t h e p y r i m i d i n e r i n g o f t h e a n t i b i o t i c came f r o m c y t o s i n e d i r e c t l y a n d sugar moiety from g l u c o s e ; a r g i n i n e s e r v e d as t h e p r e c u r s o r f o r b l a s t i d i c a c i d , and t h e N - m e t h y l group o f b l a s t i d i c a c i d a r o s e from m e t h i o n i n e . M i s a t o and h i s co-workers have s t u d i e d t h e b i o c h e m i c a l p r o p e r t i e s o f b l a s t i c i d i n S on _P. o r y z a e . They f o u n d t h e c u r a t i v e e f f e c t o f b l a s t i c i d i n S on r i c e b l a s t due t o a s t r o n g i n h i b i t o r y a c t i o n on m y c e l i a l g r o w t h o f t h e p a t h o g e n , and r e p o r t e d t h a t t h e a n t i b i o t i c m a r k e d l y i n h i b i t e d t h e i n c o r p o r a t i o n o f Rel a b e l e d amino a c i d i n t o p r o t e i n i n t h e c e l l - w a l l s y s t e m o f ]?. o r y z a e ( 1 4 ) , w h i l e m e t a b o l i c pathways i n c l u d i n g g l y c o l y s i s , s u c c i n i c d e h y d r o g e n a s e s y s t e m , e l e c t r o n t r a n s p o r t s y s t e m , and o x i d a t i v e p h o s p h o r y l a t i o n s y s t e m o r i n c o r p o r a t i o n o f ^2p i n t o t h e n u c l e i c a c i d w e r e n o t i n h i b i t e d b y b l a s t i c i d i n S ( 1 5 , 1 6 ) . The mode o f a c t i o n o f t h i s a n t i b i o t i c on t h e m o l e c u l a r b a s i s i n d e ­ t a i l i s n o t known s o f a r w i t h any c e r t a i n t y , b u t c e r t a i n p r o c e s s e s r e l a t e d t o p e p t i d y l transferase a c t i v i t y a r ei n h i b i t e d by b l a s t i ­ c i d i n S (17,18).

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch010

1

1

1

! !

2) Biological properties: B l a s t i c i d i n S has a wide range of b i o l o g i c a l a c t i v i t i e s . Besides i t s s i g n i f i c a n t i n h i b i t o r y e f f e c t s on t h e g r o w t h o f ]?. o r y z a e , i t a l s o e x h i b i t s o t h e r a n t i ­ m i c r o b i a l ( 7 ) , and a n t i - v i r a l (19) a s w e l l a s a n t i - t u m o r a c t i v i ­ t i e s ( 2 0 ) , t h o u g h t h e m e d i c i n a l a p p l i c a t i o n s a r e impeded b y i t s toxic properties. I n t h e case o f spraying i n t h e f i e l d t o pro­ tect r i c e b l a s t , thee f f e c t i v e concentration of b l a s t i c i d i n S i s u s u a l l y 10 t o 20 ppm ( 1 - 3 g b l a s t i c i d i n S / 1 0 a ) , b u t i t o c c a s i o n a l l y c a u s e s c h e m i c a l i n j u r y on r i c e l e a v e s when s p r a y e d b e y o n d t h e c o n c e n t r a t i o n d e s c r i b e d above. The a p p l i c a t i o n b y d u s t i n g o c c a s i o n a l l y causes c o n j u n c t i v i t i s i f i t a c c i d e n t a l l y c o n t a c t s t h e eyes, a l t h o u g h no a c c i d e n t has been r e p o r t e d i n t h e c a s e o f t h e s p r a y o f w e t t a b l e powder o r s o l u t i o n . Such t o x i c e f f e c t on mammals i s t h e most u n f a v o r a b l e c h a r a c t e r i s t i c o f b l a s t i c i d i n S. Many a t t e m p t s h a v e b e e n made t o remedy t h i s d e ­ f e c t o f b l a s t i c i d i n S. S u g i m o t o (21) f o u n d a s i m p l e method t o a l l e v i a t e e y e i r r i t a t i o n c a u s e d b y b l a s t i c i d i n S; t h e a d d i t i o n o f calcium acetate t o b l a s t i c i d i n S dust (5% a d d i t i o n ) s p e c i f i c a l l y r e d u c e d t h e e y e t r o u b l e w i t h o u t i n f l u e n c e on a n t i b l a s t e f f e c t , t h o u g h o t h e r mammalian t o x i c i t y o r p h y t o t o x i c i t y o f t h e a n t i ­ b i o t i c are also not affected. T h i s i m p r o v e d d u s t i s now u s e d p r a c t i c a l l y f o r a g r i c u l t u r a l use. The b e h a v i o r a n d f a t e o f b l a s t i c i d i n S i n t h e environment were i n v e s t i g a t e d u s i n g r a d i o -

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch010

PESTICIDE C H E M I S T R Y IN T H E 2 0 T H C E N T U R Y

Figure 2.

Structure of kasugamycin

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch010

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a c t i v e compounds p r e p a r e d b i o s y n t h e t i c a l l y f r o m C - c y t o s i n e and C - L - m e t h i o n i n e ( 2 2 ) . The s p r a y e d a n t i b i o t i c was l o c a t e d on t h e s u r f a c e o f t h e r i c e p l a n t a n d l i t t l e was d i f f u s e d o r t r a n s p o r t e d i n t o t h e t i s s u e . From t h e wound o r i n f e c t e d p a r t , however, t h e compound was i n c o r p o r a t e d and t r a n s l o c a t e d m a i n l y t o u p p e r p a r t . The compound l o c a t e d a t t h e p l a n t s u r f a c e was decomposed b y s u n ­ l i g h t a n d gave r i s e t o c y t o s i n e a s t h e m a i n d e g r a d a t i o n product. A considerable quantity o f b l a s t i c i d i n S sprayed f e l l t o t h e g r o u n d a n d was a d s o r b e d on t h e s o i l s u r f a c e t i g h t l y . Further­ more, s i g n i f i c a n t g e n e r a t i o n o f - ^ C - c a r b o n d i o x i d e f r o m t h e - ^ C i ­ b l a s t i c i d i n S t r e a t e d s o i l was o b s e r v e d , and s e v e r a l m i c r o b e s u s u a l l y i n h a b i t i n g t h e paddy f i e l d w e r e f o u n d t o make t h e b i o l o ­ g i c a l a c t i v i t y o f b l a s t i c i d i n S lower. From t h e r e s u l t s o b t a i n e d , Y a m a g u c h i et_ a l . s u p p o s e d t h a t a f t e r a p p l i c a t i o n t o t h e c r o p a t very low c o n c e n t r a t i o n , t h e a n t i b i o t i c might be r a p i d l y broken down i n t h e e n v i r o n m e n t , s o t h a t t h e r e may b e no d a n g e r o f e n ­ v i r o n m e n t a l p o l l u t i o n and food contamination. Kasugamycin. K a s u g a m y c i n i s a w a t e r - s o l u b l e and b a s i c a n t i ­ b i o t i c produced by Streptomyces kasugaensis (23). F o l l o w i n g t h e d e v e l o p m e n t o f b l a s t i c i d i n S, k a s u g a m y c i n h a s b e e n u s e d a s a n a g r i c u l t u r a l a n t i b i o t i c f o r r i c e b l a s t c o n t r o l i n Japan s i n c e 1965. This a n t i b i o t i c controls r i c e b l a s t disease a t a concentra­ t i o n a s l o w a s a b o u t 20 ppm. I t c a n b e s a f e l y u s e d w i t h o u t a n y t o x i c i t y on c r o p s , and w i t h v e r y l o w t o x i c i t y t o mammals. These advantages a r e t h e main r e a s o n s t h a t b l a s t i c i d i n S i s l o s i n g ground t o kasugamycin. However, r e c e n t l y , t h e v i r u l e n c e o f kasugamycin-resistant s t r a i n i n paddy f i e l d h a s r a i s e d a s e r i o u s problem i n r i c e b l a s t c o n t r o l by kasugamycin. 1) C h e m i s t r y and mode o f a c t i o n : The c h e m i c a l s t r u c t u r e o f k a s u g a m y c i n was s t u d i e d b y S u h a r a elt a l . (24,25) b y c h e m i c a l methods a n d b y I k e k a w a e t a l . (26) b y X - r a y d i f f r a c t i o n a n a l y s i s . As shown i n F i g u r e 2, t h e m o l e c u l e o f k a s u g a m y c i n c o n s i s t s o f t h r e e m o i e t i e s w h i c h a r e D - i n o s i t o l , kasugamine (2,3,4,6-tetrad e o x y - 2 , 4 - d i a m i n o h e x o p y r a n o s e ) and an i m i n o a c e t i c a c i d s i d e c h a i n . N a k a j i m a and h i s a s s o c i a t e s s t u d i e d t h e s y n t h e s i s o f k a s u g a m y c i n , and s u c c e e d e d i n s y n t h e s i z i n g k a s u g a n o b i o s a m i n e and r e l a t e d com­ pounds ( 2 7 , 2 8 ) ; t h a t means t h e t o t a l s y n t h e s i s o f k a s u g a m y c i n b y t h e i n t r o d u c t i o n o f t h e o x a l i m i d y l group i n t o k a s u g a n o b i o s a m i n e . K a s u g a m y c i n e n t e r s i n t o t h e p l a n t t i s s u e , a n d shows b o t h p r o t e c t i v e and c u r a t i v e a c t i o n . I t does n o t i n h i b i t s p o r e g e r m i ­ n a t i o n even a t a c o n c e n t r a t i o n o f 120 ug/ml. I t s effect against £.· o^yzae comes o n l y t o e x p r e s s i o n i n t h e p l a n t a n d i n v i t r o a t l o w pH ( 2 9 ) . T a n a k a jet a l . (30) r e p o r t e d t h a t k a s u g a m y c i n i n ­ h i b i t e d p r o t e i n s y n t h e s i s i n c e l l f r e e s y s t e m s o f ]?. o r y z a e . Kasugamycin i n h i b i t s p r o t e i n s y n t h e s i s i n E s c h e r i c h i a c o l i b y i n t e r f e r i n g w i t h t h e b i n d i n g o f a m i n o a c y l - t R N A t o mRNA-30 S r i b o s o m a l s u b u n i t complex. The compound does n o t c a u s e m i s c o d i n g .

PESTICIDE C H E M I S T R Y IN

176

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2) B i o l o g i c a l p r o p e r t i e s : K a s u g a m y c i n s e l e c t i v e l y i n h i b i t e d t h e g r o w t h o f P. ovyzae and some b a c t e r i a i n c l u d i n g Pseudomonas s p e c i e s , and showed l i t t l e o r no a c t i v i t y a g a i n s t o t h e r f u n g i tested. The a n t i b i o t i c d i d n o t show a c u t e o r c h r o n i c t o x i c i t y t o m i c e , r a t s , r a b b i t s , d o g s , monkeys and human b e i n g s . The o r a l LD f o r m i c e was 2 g/kg. A t a c o n c e n t r a t i o n o f 1,000 ppm t h e r e was no t o x i c i t y t o f i s h . K a s u g a m y c i n i s now u s e d i n a l a r g e scale against r i c e blast. I t c o n t r o l s r i c e b l a s t when s p r a y e d a t a b o u t 20 - 40 ppm aqueous s o l u t i o n . For p r a c t i c a l disease c o n t r o l k a s u g a m y c i n i s m a i n l y a p p l i e d a s a d u s t , c o n t a i n i n g 0.3 % o f a c t i v e i n g r e d i e n t . No i n j u r y was o b s e r v e d t o many o t h e r p l a n t s . The d e v e l o p m e n t o f r e s i s t a n c e i n f u n g i t o k a s u g a m y c i n has been r e p o r t e d from l a b o r a t o r y experiments, but not i n the f i e l d s f o r some y e a r s a f t e r a p p l i c a t i o n o f t h e a n t i b i o t i c . However, s i n c e 1971, t h e d e v e l o p m e n t o f a k a s u g a m y c i n - r e s i s t a n t s t r a i n o f r i c e b l a s t f u n g u s i n t h e f i e l d s has become a s e r i o u s p r o b l e m ( 3 1 ) . A f t e r k a s u g a m y c i n r e s i s t a n t s t r a i n s had b e e n d e t e c t e d i n t h e f i e l d , t h e c o m b i n e d f o r m u l a t i o n s o f k a s u g a m y c i n and c h e m i c a l s w i t h d i f f e r e n t a c t i o n mechanisms h a v e b e e n p r a c t i c a l l y u s e d .

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch010

5 0

Polyoxins. The p o l y o x i n s , a new g r o u p o f p e p t i d y l - p y r i m i d i n e n u c l e o s i d e a n t i b i o t i c s , a r e p r o d u c e d by Streptomyoes oaoaoi v a r . asoensis (32,33). P o l y o x i n s a r e composed o f t h i r t e e n components (A - M) o f some c l o s e l y r e l a t e d " p e p t i d i c n u c l e o s i d e s " as r e f e r r e d by I s o n o and S u z u k i ( 3 4 ) . They c a n be s a f e l y u s e d w i t h no t o x i c i t y t o man, l i v e s t o c k , f i s h and p l a n t . Such e x c e l l e n t c h a r a c t e r i s t i c s may be due t o t h e f a c t t h a t p o l y o x i n s s e l e c t i v e l y i n h i b i t the s y n t h e s i s of c e l l w a l l c h i t i n of s e n s i t i v e f u n g i , as was r e p o r t e d by M i s a t o and h i s c o - w o r k e r s ( 3 5 - 3 8 ) . P o l y o x i n s have b e e n w i d e l y u s e d f o r t h e p r o t e c t i o n a g a i n s t some p a t h o g e n i c f u n g i

s u c h a s Altemaria miyabeanus

kikuohiana,

i n Japan s i n c e

Pellioularia

sasakii, and

Coehlibolus

1967.

1) C h e m i s t r y and mode o f a c t i o n : S t r u c t u r e s o f a l l p o l y o x i n s were g i v e n by I s o n o et al. (39) a s d e p i c t e d i n F i g u r e 3. Among p o l y o x i n s , C component i s t h e s m a l l e s t , and t h o u g h i t l a c k s a n t i ­ f u n g a l a c t i v i t y i t was a k e y compound t o e l u c i d a t e t h e s t r u c t u r e of p o l y o x i n s s i n c e h y d r o l y t i c degradation of a l l the p o l y o x i n s afforded p o l y o x i n C or i t s analogues. I s o n o and S u z u k i (40) assigned the s t r u c t u r e , l-ft-iS'-amino-S'-deoxy-D-allofuranuronosyl) - 5 - h y d r o x y m e t h y l u r a c i l t o p o l y o x i n C by c h e m i c a l and p h y s i c a l t e c h n i q u e s , and a s i n g l e - c r y s t a l X - r a y d i f f r a c t i o n a n a l y s i s o f Nb r o s y l p o l y o x i n C c o n f i r m e d the s t r u c t u r e (41). T h i s prompted the t o t a l s y n t h e s i s o f p o l y o x i n J by K u z u h a r a et al. ( 4 2 ) . In s t u d y i n g t h e mechanism o f f u n g i c i d a l a c t i o n o f p o l y o x i n s , E g u c h i et al. (43) o b s e r v e d a s p e c i f i c p h y s i o l o g i c a l a c t i o n a g a i n s t Altevnaria spp. i n i n h i b i t i n g i t s g r o w t h ; p o l y o x i n s c a u s e d m a r k e d a b n o r m a l b u l b o u s phenomenon on germ t u b e s o f s p o r e and h y p h a l t i p s o f t h e p a t h o g e n a t l o w c o n c e n t r a t i o n , and t h i s a b n o r m a l l y s w o l l e n s p o r e became n o n - i n f e c t i o u s . I t was a l s o r e p o r t e d t h a t t h e

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Ο

Ri

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Polyoxin

R

2

A

CH OH

*

OH

Β

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HO

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COOH

HO

OH

Ε

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F

COOH

*

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6

CH 0H 2

HO

H

H

CH

a

*

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3

HO

OH

Κ

H

*

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Figure 3.

R3

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Structure of polyoxins

178

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Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch010

lz

i n c o r p o r a t i o n of *C-glucosamine i n t o c e l l w a l l c h i t i n of Coohliobolus miyabeanus was m a r k e d l y i n h i b i t e d by p o l y o x i n D, w i t h o u t i n h i b i t o r y e f f e c t on r e s p i r a t i o n and s y n t h e s i s o f m a c r o m o l e c u l e s s u c h as p r o t e i n o r n u c l e i c a c i d s ( 4 4 ) . Endo and M i s a t o (36) showed i n t h e i r k i n e t i c s t u d i e s o f t h e c e l l - f r e e s y s t e m o f Neurospora arassa t h a t p o l y o x i n D s t r o n g l y i n h i b i t s t h e i n c o r p o r a ­ t i o n of N - a c e t y l g l u c o s a m i n e (GlcNAc) i n t o c h i t i n i n c o m p e t i t i v e manner b e t w e e n UDP-GlcNAc and p o l y o x i n D. More r e c e n t l y H o r i et at. (38) r e p o r t e d t h e r e l a t i o n b e t w e e n p o l y o x i n s t r u c t u r e and i n h i b i t o r y a c t i v i t y on c h i t i n s y n t h e t a s e . According to t h e i r k i n e t i c a n a l y s i s , the carbamoyl polyoxamic a c i d moiety of p o l y o x i n s w o u l d h e l p t o s t a b i l i z e t h e p o l y o x i n enzyme c o m p l e x and the p y r i m i d i n e n u c l e o s i d e moiety of the a n t i b i o t i c s would a l s o f i t i n t o b i n d i n g s i t e of the p r o t e i n . Therefore the e x c e l l e n t c h a r a c t e r i s t i c s o f p o l y o x i n s may be due t o t h e f a c t t h a t t h e a n t i b i o t i c s i n h i b i t the c e l l w a l l s y n t h e s i s of s e n s i t i v e f u n g i but have no i n f l u e n c e on o t h e r o r g a n i s m s i n c l u d i n g mammals, s i n c e t h e r e e x i s t no c e l l w a l l s i n a n i m a l c e l l s . 2) B i o l o g i c a l p r o p e r t i e s : P o l y o x i n s i n h i b i t t h e g r o w t h o f some f u n g i b u t a r e i n a c t i v e a g a i n s t b a c t e r i a and y e a s t . A l l the p o l y o x i n s e x c e p t C and I showed s e l e c t i v e a n t i f u n g a l a c t i v i t y a g a i n s t v a r i o u s p l a n t p a t h o g e n i c f u n g i ( 4 5 ) . Among p o l y o x i n s , p o l y o x i n D was most e f f e c t i v e f o r r i c e s h e a t h b l i g h t p a t h o g e n , Pellicularia sasakii, w h e r e a s Β and L w e r e e f f e c t i v e f o r p e a r s p o t f u n g u s and a p p l e c o r k s p o t f u n g u s a t 50 t o 100 ppm. Polyoxin c o m p l e x has b e e n u s e d i n p r a c t i c e i n d u p l i c a t e f o r m s ; p o l y o x i n D r i c h f r a c t i o n f o r t h e s h e a t h b l i g h t c o n t r o l , and Β r i c h f r a c t i o n f o r d i s e a s e s c a u s e d by Altemaria spp. As f o r i t s t o x i c i t y , o r a l a d m i n i s t r a t i o n a t 15 g/kg and i n j e c t i o n a t 800 mg/kg t o m i c e d i d n o t c a u s e any a d v e r s e e f f e c t , n o r i s i t t o x i c t o f i s h d u r i n g 72 h o u r s p e r i o d o f e x p o s u r e a t 10 ppm. M o r e o v e r , f o l i a r s p r a y s o f 200 ppm p o l y o x i n s have p r o d u c e d no p h y t o t o x i c i t y on most c r o p s , and e s p e c i a l l y on r i c e p l a n t no i n j u r y was o b s e r v e d e v e n a t 800 ppm a p p l i c a t i o n ( 3 3 , 4 6 ) . R e c e n t l y , N i s h i m u r a et at. (47) h a v e r e p o r t e d t h e d i s c o v e r y o f p o l y o x i n r e s i s t a n t s t r a i n s o f A. kikuohiana i n some o r c h a r d s o f T o t t o r i P r e f e c t u r e , J a p a n . H o r i et al. (48) s u g g e s t e d t h a t t h e r e s i s t a n c e i s c a u s e d by a l o w e r e d p e r m e a b i l i t y o f t h e a n t i b i o t i c t h r o u g h t h e c e l l membrane i n t o t h e s i t e o f c h i t i n s y n t h e s i s . M i t a n i and I n o u e (49) f o u n d t h a t t h e i n h i b i t i o n o f m y c e l i a l g r o w t h o f P. sasakii, by p o l y o x i n s was p r o t e c t e d by g l y c y l - L a l a n i n e , g l y c y l - D , L - v a l i n e and D , L - a l a n y l g l y c i n e . T h e r e f o r e , t h e p e p t i d e s may a c t a s a n t a g o n i s t s t o t h e i n c o r p o r a t i o n o f p o l y o x i n s i n t o the c e l l of the fungus. Validamycin. V a l i d a m y c i n A (VM-A) i s a new a n t i f u n g a l a n t i ­ b i o t i c r e c e n t l y developed i n Japan f o r the c o n t r o l of r i c e sheath b l i g h t (50-52). I t was i s o l a t e d f r o m t h e c u l t u r e f i l t r a t e o f Streptomyaes hygroscopicus v a r . limoneus, w h i c h a l s o p r o d u c e d f i v e

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a d d i t i o n a l components d e s i g n a t e d v a l i d a m y c i n Β t o F, t o g e t h e r w i t h v a l i d o x y l a m i n e A and Β (52,53). VM-A c a n be u s e d w i t h o u t i n j u r y t o p l a n t s , and w i t h v e r y l o w t o x i c i t y t o mammals ( 5 4 ) . A l m o s t no t o x i c i t y was a l s o o b s e r v e d f o r b i r d s , f i s h and i n s e c t s . 1) C h e m i s t r y and mode o f a c t i o n : The c h e m i c a l s t r u c t u r e o f v a l i d a m y c i n A was d e t e r m i n e d b y H o r i i , Kameda and t h e i r c o - w o r k e r s t o be N - [ ( l s ) - ( l , 4 , 6 / 5 ) - 3 - h y d r o x y m e t h y l - 4 , 5 , 6 - t r i h y d r o x y c y c l o h e x - 2 enyl][Ο-β-D-glucopyranosyl-(l->3 ) - ( l s ) - ( l , 2 , 4 / 3 , 5 ) - 2 , 3 , 4 - t r i h y d r o x y - 5 - h y d r o x y m e t h y l c y c l o h e x y l ] amine a s shown i n F i g u r e 4 (53,55,56,57). As f o r mode o f a c t i o n o f v a l i d a m y c i n A, Wakae and M a t s u u r a ( 5 8 ) showed t h a t VM-A i n h i b i t s b i o s y n t h e s i s o f i n o s i t o l i n P . sasakii, and t h e y s u p p o s e d t h a t i n o s i t o l may be i n d i s p e n s a b l e f o r t h e n o r m a l g r o w t h and p a t h o g e n i c a c t i v i t y o f t h e f u n g u s . A l t h o u g h r e d u c t i o n o f p a t h o g e n i c i t y i n d u c e d b y VM-A was remarkably r e c o v e r e d by t h e p r e m i x i n g o f i n o s i t o l i n t h e i r e x p e r i ­ ment, f u r t h e r i n v e s t i g a t i o n w i l l be r e q u i r e d t o s o r t o u t t h e s p e c i f i c s i t e a n d t y p e o f a c t i o n o f VM-A. 2) B i o l o g i c a l p r o p e r t i e s : A n t i m i c r o b i a l a c t i v i t y o f VM-A a g a i n s t a b o u t 3,000 s p e c i e s o f f u n g i and b a c t e r i a was n o t d e t e c t e d w i t h o r d i n a r y methods ( 5 1 , 5 9 ) , a n d a l s o d i s t u r b a n c e o f m i c r o f l o r a on r i c e p l a n t a n d c r o p f i e l d was n o t o b s e r v e d ( 5 8 ) . Wakae a n d M a t s u u r a (60) f o u n d no p h y t o t o x i c i t y o n o v e r 150 s p e c i e s o f p l a n t s s p r a y e d w i t h VM-A e v e n a t a c o n c e n t r a t i o n o f 1,000 ppm. Further­ more, a c u t e a n d s u b a c u t e t o x i c i t i e s t o mammals w e r e m a r k e d l y l o w ; i n o r a l a d m i n i s t r a t i o n o f v a l i d a m y c i n A a t t h e d o s e o f 10 g/kg t o m i c e and r a t s , o r i n s u b c u t a n e o u s and i n t r a v e n o u s a d m i n i s t r a t i o n a t t h e d o s e o f 2 g/kg t o m i c e , a l l a n i m a l s e x a m i n e d s u r v i v e d w i t h ­ o u t any change f o r 7 days ( 5 1 ) . VM-A i s a m a i n component o f v a l i d a m y c i n c o m p l e x and i s s p e c i f i c a l l y e f f e c t i v e a g a i n s t c e r t a i n p l a n t d i s e a s e s c a u s e d b y Rhizoctonia s p p . , s u c h a s web b l i g h t , b u d r o t , d a m p i n g - o f f s e e d d e c a y , r o o t r o t and b l a c k s c u r f o f s e v e r a l c r o p s and s o u t h e r n b l i g h t o f v e g e t a b l e s a s w e l l a s s h e a t h b l i g h t o f r i c e p l a n t ( 5 8 ) . Though t h e a n t i b i o t i c showed n e i t h e r c i d a l n o r s t a t i c a c t i o n o f Rhizoctonia s p p . , i t c a u s e d an a b n o r m a l b r a n c h i n g a t t h e t i p s o f hyphae o f t h e p a t h o g e n , f o l l o w e d b y c e s s a t i o n o f f u r t h e r d e v e l o p m e n t ( 5 1 ) . When i t was a p p l i e d i n t h e e a r l y l o g a r i t h m i c p h a s e o f l e s i o n e x p a n s i o n on r i c e p l a n t , s u f f i c i e n t c o n t r o l was a c h i e v e d b y one s p r a y i n g o f 30 ppm VM-A s o l u t i o n ( 6 0 ) . VM-A h a s b e e n c o m m e r c i a l l y u s e d upon s h e a t h b l i g h t d i s e a s e s i n c e 1973. V a l i d a m y c i n s h a v e b e e n shown t o be s u s c e p t i b l e t o m i c r o b i a l a t t a c k and t h e i r a d d i t i o n t o s o i l r e s u l t ­ ed i n c o m p l e t e l o s s o f b i o l o g i c a l a c t i v i t y b y s o i l m i c r o b e s . I t s h a l f - l i f e i n s o i l was l e s s t h a n 4 h o u r s . M i c r o b i a l degrada­ t i o n o f VM-A b y Pseudomonas denitrificans gave r i s e t o D - g l u c o s e and v a l i d o x y l a m i n e A, w h i c h was f u r t h e r decomposed i n t o v a l i e n a m i n e , v a l i d a m i n e and o t h e r l o w e r compounds ( 6 1 ) . V a l i d a m y c i n A has been p r a c t i c a l l y used t o p r o t e c t sheath b l i g h t o f r i c e p l a n t i n t h e f o r m u l a t i o n s o f 3 % s o l u t i o n o r 0.3 % d u s t .

180

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PESTICIDE C H E M I S T R Y IN T H E 2 0 T H C E N T U R Y

Figure 5.

Structure of ezomycin

10.

MisATO

Agricultural

181

Antibiotics

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch010

R e s i d u e s i n r i c e g r a i n s and s t r a w s w e r e l e s s t h a n e a c h l i m i t by gas c h r o m a t o g r a p h y ( 6 2 ) .

detectable

Ezomycins. E z o m y c i n s a r e a n t i f u n g a l a n t i b i o t i c s p r o d u c e d by a s t r a i n o f Streptomyces v e r y s i m i l a r t o S. kitazawaensis. T a k a o k a et al. (63) i s o l a t e d a c o m p l e x o f t h e a n t i b i o t i c s f r o m t h e c u l t u r e f i l t r a t e o f t h e p r o d u c i n g o r g a n i s m and r e p o r t e d t h a t t h e c o m p l e x has u n i q u e b i o l o g i c a l a c t i v i t y i n s u p p r e s s i n g the g r o w t h o f v e r y l i m i t e d s p e c i e s o f p h y t o p a t h o g e n i c f u n g i , s u c h as Sclerotica and Botrytis spp. S i n c e t h e c o m p l e x showed r e m a r k a b l e a n t i m i c r o b i a l a c t i v i t y a g a i n s t Sclerotinia sclerotiorvm de B a r y t h a t c a u s e s s t e m r o t i n k i d n e y b e a n p l a n t s (Phaseolus vulgaris L.), i s o l a t i o n and c h a r a c t e r i z a t i o n o f e a c h component o f e z o m y c i n s w e r e c a r r i e d o u t by S a k a t a et al. (64). According to Sakata et al. e z o m y c i n s a r e new p y r i m i d i n e n u c l e o s i d e s , and t h e p r e s e n c e of L - c y s t a t h i o n i n e i n ezomycin molecule i s r e s p o n s i b l e f o r specific antifungal activity. Recently they e l u c i d a t e d the c h e m i c a l s t r u c t u r e o f a l l t h e e z o m y c i n s (65-67) ; F i g u r e 5 shows t h e c h e m i c a l s t r u c t u r e o f e z o m y c i n A. T h i s a n t i b i o t i c was registered a s an a g r i c u l t u r a l a n t i b i o t i c f o r t h e c o n t r o l o f s t e m r o t o f k i d n e y b e a n i n 1970, b u t has s c a r c e l y b e e n on t h e m a r k e t since then. 9

Antibacterial

antibiotic

Cellocidin. C e l l o c i d i n i s an a n t i b i o t i c p r o d u c e d f r o m Streptomyces chibaensis (68,69). I t i s an a c e t y l e n e d i c a r b o x y a m i d e c o n t a i n i n g o n l y f o u r c a r b o n atoms as shown i n F i g u r e 6. As i t s c h e m i c a l s t r u c t u r e i s so s i m p l e , i t i s e a s y t o s y n t h e s i z e chemically. T e c h n i c a l grade c e l l o c i d i n f o r commercial formula­ t i o n s i s now s y n t h e s i z e d f r o m f u m a r i c a c i d o r b u t y n e d i o l . C e l l o c i d i n shows an e x c e l l e n t p r e v e n t i v e e f f e c t a g a i n s t r i c e bacterial l e a f b l i g h t when s p r a y e d on r i c e p l a n t s a t 100 t o 200 ppm ( 7 0 ) . I t s t o x i c i t y when i n j e c t e d i n t r a v e n o u s l y i s h i g h ( L D o t o m i c e , l l m g / k ^ ) , b u t i n o r a l a d m i n i s t r a t i o n and s k i n a p p l i c a t i o n i t i s n o t so h i g h l y t o x i c ( L D t o m i c e , 89.2 - 125 mg/kg and L D o t o m i c e , 667 mg/kg r e s p e c t i v e l y ) . C e l l o c i d i n has b e e n p r a c t i c a l l y u s e d s i n c e 1964. However, i t s c o n s u m p t i o n has b e e n r e m a r k a b l y d e c r e a s e d due t o i t s p h y t o t o x i c i t y . The a n t i b a c t e r i a l a c t i o n o f c e l l o c i d i n was a n t a g o n i z e d by c y s t e i n e o r g l u t a t h i o n e , w h i c h i n d i c a t e s i n t e r a c t i o n w i t h SH-groups. A s t u d y of s e v e r a l m e t a b o l ­ i c s y s t e m s f r o m Xanthomonas oryzae r e v e a l e d that c e l l o c i d i n s e l e c t i v e l y i n h i b i t e d N A D - r e q u i r i n g d e h y d r o g e n a s e , and e s p e c i a l l y i n t h e p a t h w a y f r o m α-ketoglutamic a c i d t h r o u g h s u c c i n y l Co A t o s u c c i n i c a c i d a t t h e minimum g r o w t h i n h i b i t o r y c o n c e n t r a t i o n o f 10 ppm (71). 5

5 0

Insecticidal

5

antibiotic

Tetranactin.

T e t r a n a c t i n , a new

miticidal antibiotic,

was

PESTICIDE

C H E M I S T R Y I N T H E 20TH

C —CONH,

111

C —C0NH

Structure of cellocidin

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch010

Figure 6.

2

Figure 7.

Structure of tetranactin

CENTURY

10.

MisATO

Agricultural

Antibiotics

183

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch010

i s o l a t e d as c r y s t a l l i n e rhombic prisms from the f i l t e r cake o f t h e f e r m e n t e d b r o t h o f Streptomyces aureus s t r a i n S-3466 ( 7 2 ) . The a n t i b i o t i c exerted remarkable p e s t i c i d a l a c t i v i t y s p e c i f i c a l l y a g a i n s t t h e a d u l t s o f c a r m i n e m i t e a n d showed v e r y weak t o x i c i t y to a warm-blooded a n i m a l . A l s o i t showed no p h y t o t o x i c i t y t o a p p l e , m a n d a r i n o r a n g e a n d t e a , when s p r a y e d a t h i g h c o n c e n t r a t i o n (73) . The m i t i c i d a l p r o p e r t y o f t e t r a n a c t i n i n t h e f i e l d s o f a p p l e a n d t e a h a d b e e n e v a l u a t e d i n J a p a n s i n c e 1968, a n d t e t r a n a c t i n h a s been used a s a m i t i c i d e f o r p l a n t s s i n c e 1974. 1) C h e m i s t r y a n d mode o f a c t i o n : Ando et al. (72) i s o l a t e d the a c t i v e p r i n c i p l e i n c r y s t a l l i n e form by e x t r a c t i n g t h e m y c e l i a l c a k e o f S. aureus w i t h acetone followed by s i l i c a g e l c o l u m n c h r o m a t o g r a p h y . They a l s o showed t h a t S. aureus produces, a l o n g w i t h t e t r a n a c t i n , two o t h e r s t r u c t u r a l l y r e l a t e d m a c r o t e t r o l i d e a n t i b i o t i c s , i . e . , d i n a c t i n and t r i n a c t i n , i n minor amount. From t h e s t u d i e s o n t h e c h e m i c a l c h a r a c t e r i s t i c s o f t e t r a n a c t i n , i t was f o u n d t h a t t h e a n t i b i o t i c a l s o b e l o n g s t o t h e c l a s s o f m a c r o t e t r o l i d e a n t i b i o t i c and i s a c y c l i c p o l y e s t e r composed o f f o u r u n i t s o f h o m o n o n a c t i c a c i d , a s shown i n F i g u r e 7 (74) • The s t e r e o c h e m i c a l s t r u c t u r e was c l a r i f i e d w i t h t h e u s e o f X - r a y c r y s t a l l o g r a p h y b y I i t a k e et al. (75). A s f o r mode o f a c t i o n o f t e t r a n a c t i n , Ando et al. (76) o b s e r v e d t h a t t e t r a n a c t i n i s an u n c o u p l e r i n c o c k r o a c h m i t o c h o n d r i a and supposed t h a t t h e a n t i b i o t i c caused t h e leakage o f a l k a l i c a t i o n s such as K through t h e l i p i d l a y e r o f t h e biomembrane i n m i t o c h o n d r i a , f o l l o w e d b y uncoupling. +

2) B i o l o g i c a l p r o p e r t i e s : S p e c i f i c i t y i n b i o l o g i c a l a c t i v i t y i s a unique property o f t e t r a n a c t i n ; i t exerted potent p e s t i c i d a l a c t i v i t y a g a i n s t the a d u l t s o f a carmine s p i d e r m i t e a l o n e , L D o f o r w h i c h i s 4.8 y g / m l w i t h t h e s p r a y method ( 7 7 ) . A z u k i b e a n w e e v i l and l a r v a o f m o s q u i t o were m o d e r a t e l y s e n s i t i v e to the a n t i b i o t i c , w h i l e o t h e r p e s t s such a s house f l y and c o c k r o a c h w e r e i n s e n s i t i v e . I n a d d i t i o n , i t was o b s e r v e d t h a t t h e o v i c i d a l a c t i v i t y o f the a n t i b i o t i c a g a i n s t t h e s e n s i t i v e m i t e s i s n o t s o s i g n i f i c a n t , w h i c h a p p e a r e d t o b e one o f t h e weak p o i n t s o f tetranactin. The m i t i c i d a l a c t i v i t y , h o w e v e r , was c o n f i r m e d i n the t r i a l s . T e t r a n a c t i n s u s p e n s i o n s were s p r a y e d on a p p l e t r e e s on w h i c h l e a v e s Kanzawa s p i d e r and European r e d m i t e were n a t u r a l ­ l y p a r a s t i c ; p r o l i f e r a t i o n o f b o t h m i t e s were c o m p l e t e l y retarded d u r i n g 32 d a y s o f t h e e x p e r i m e n t . Another c h a r a c t e r i s t i c o f tetranactin i s i t s safety. Ando et al. (72) r e p o r t e d t h a t m i c e t o l e r a t e d a n i n t r a p e r i t o n e a l a d m i n i s t r a t i o n o f 300 mg/kg a n d a n o r a l a d m i n i s t r a t i o n o f 15 g/kg. They a l s o o b s e r v e d t h a t a c u t e t o x i c i t y o f t h e a n t i b i o t i c i s v e r y l o w ; t h e o r a l L D s o ' s a r e more t h a n 2 g/kg t o r a t s , g u i n e a p i g s , q u a i l s a n d r a b b i t s ( 7 6 ) . They suggested that t h e low t o x i c i t y i s p a r t l y a t t r i b u t a b l e t o t h e poor a b s o r p t i o n by a n i m a l s . When C - t e t r a n a c t i n p r e p a r e d b y b i o s y n t h e s i s was a d m i n i s t e r e d o r a l l y t o m i c e , i t was r e v e a l e d t h a t 5

1 4

184

PESTICIDE C H E M I S T R Y IN

THE

20TH

t h e a n t i b i o t i c i s l i t t l e a b s o r v e d so t h a t t h e d i s t r i b u t i o n v a r i o u s o r g a n s was n e g l i g i b l e and a l m o s t a l l r a d i o a c t i v i t y r e c o v e r e d i n f e c e s 72 h o u r s a f t e r a d m i n i s t r a t i o n ( 7 6 ) . Other promising

CENTURY

in was

antibiotics

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch010

1. H e r b i c i d a l a n t i b i o t i c M e t h o x y p h e n o n e (An a n i s o m y c i n a n a l o g u e ) . Yamada et αϊ· (78) f o u n d a s t r a i n o f Streptomyoes t o p r o d u c e two p l a n t - r e g u l a t i n g s u b s t a n c e s , w h i c h w e r e l a t e r i d e n t i f i e d as a n i s o m y c i n (79) and toyokamycin (80). They o b s e r v e d t h a t a n i s o m y c i n e x e r t e d s t r o n g g r o w t h - i n h i b i t o r y a c t i v i t y on t h e r o o t s and s h o o t s o f a l l t h e p l a n t s t e s t e d ( r i c e , b a r n y a r d g r a s s , c r a b g r a s s , l u c e r n e and t o m a t o ) a t 12.5 and 50 ppm, r e s p e c t i v e l y . T h e s e r e s u l t s l e d t o t h e i n v e s t i g a t i o n o f compounds h a v i n g p - m e t h o x y p h e n y l groups(pa n i s o l e d e r i v a t i v e s ) on p l a n t g r o w t h - r e g u l a t i n g a c t i v i t y , and many a n i s o l e d e r i v a t i v e s w e r e s y n t h e s i z e d and t h e i r a c t i v i t i e s w e r e t e s t e d (81). T h i s r e s u l t e d i n the f i n d i n g of i n t e r e s t i n g p l a n t g r o w t h - r e g u l a t i n g a c t i v i t i e s o f p - m e t h o x y d i p h e n y l m e t h a n e s and p-methoxybenzophenones. E s p e c i a l l y , r e m a r k a b l e h e r b i c i d a l a c t i v i t y was c o n f i r m e d f o r 3 , 3 - d i m e t h y l - 4 - m e t h o x y b e n z o p h e n o n e (methoxyphenone) i n t h e paddy f i e l d t e s t s . M e t h o x y p h e n o n e c o m p l e t e l y i n d u c e d c h l o r o s i s i n b a r n y a r d g r a s s and p r o v i d e d a s a t i s f a c t o r y h e r b i c i d a l e f f e c t a t 4 kg/ha a p p l i c a t i o n , a l t h o u g h weak c h l o r o s i s was o c c a s i o n a l l y o b s e r v e d i n r i c e s t e m a t 6 k g / h a (82). A c c o r d i n g t o I s h i d a et al., methoxyphenone i s q u i t e a s t a b l e s u b s t a n c e , b u t i s g r a d u a l l y decomposed by s u n l i g h t . In paddy f i e l d , i t a l s o seems t o be s u s c e p t i b l e t o m i c r o b i a l a t t a c k ; c o n c e n t r a t i o n o f methoxyphenone i n t h e s o i l r e a c h e d a max 2.16 ppm 7 days a f t e r a p p l i c a t i o n , b u t d e c r e a s e d t o 0.018 ppm a f t e r 30 d a y s and t o b e l o w 0.004 ppm a f t e r 60 d a y s . W h i l e t h e m e t a b o l i c f a t e o f methoxyphenone i n t h e e n v i r o n m e n t i s p r e s e n t l y u n d e r i n v e s t i g a t i o n , t h i r t e e n m e t a b o l i t i e s h a v e so f a r b e e n i d e n t i f i e d ; t h e m e t h o x y g r o u p was t r a n s f o r m e d i n t o t h e h y d r o x y g r o u p and t h e b e n z o p h e n o n e s k e l e t o n was decomposed t o w - t o l u i c a c i d and 4-hydroxy-/7?-toluic a c i d . I n a d d i t i o n , the acute t o x i c i t y of methoxyphenone t o m i c e and r a t s was f o u n d t o be more t h a n 4 g/kg independent of the a d m i n i s t r a t i o n routes (82). Therefore, m e t h o x y p h e n o n e i s c o n s i d e r e d t o be a p r o m i s i n g h e r b i c i d e w i t h a h i g h l e v e l o f s a f e t y f o r use i n the e n v i r o n m e n t . 1

2. A n t i v i r a l a n t i b i o t i c s One o f t h e most s e r i o u s p r o b l e m s on p l a n t d i s e a s e c o n t r o l i s the v i r u l e n c e of v i r u s d i s e a s e s . T r i a l s to develop a n t i v i r a l a n t i b i o t i c s h a v e b e e n e n t h u s i a s t i c a l l y c o n d u c t e d by many w o r k e r s . C o n s e q u e n t l y , many a n t i b i o t i c s h a v e b e e n r e v e a l e d t o be e f f e c t i v e on i n h i b i t i n g t h e m u l t i p l i c a t i o n o f s e v e r a l p l a n t v i r u s e s by in vitro t e s t and p o t t e s t . They a r e b l a s t i c i d i n S, l a u r u s i n , b i h o r o m y c i n , m i h a r a m y c i n , c i t r i n i n and a a b o m y c i n A e t c . However,

10.

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Antibiotics

t h e r e i s no a n t i b i o t i c virus diseases. A a b o m y c i n A. Streptomyces

hygros

185

used p r a c t i c a l l y for c o n t r o l l i n g any p l a n t

A a b o m y c i n A was i s o l a t e d f r o m c u l t u r e b r o t h o f copious

v a r . aabomyoeticus

by

Aizawa

et

at.

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch010

( 8 3 ) . By Y a m a g u c h i et al. (84) w i t h l e a f d i s c d i p p i n g method, a a b o m y c i n A showed a b o u t 80 % i n h i b i t i o n o n TMV m u l t i p l i c a t i o n i n tobacco t i s s u e s . Aabomycin A i s n o t o n l y e f f e c t i v e t o i n h i b i t t h e d i s e a s e d e v e l o p m e n t o f TMV, b u t a l s o e f f e c t i v e t o i n h i b i t t h a t o f CMV a n d AMV e t c . , w i t h p o t t e s t . Future prospects One o f t h e g r e a t e s t needs i n t h e p r e s e n t w o r l d i s p r o d u c t i o n o f food f o r b i l l i o n s o f people. A t p r e s e n t , such p r o d u c t i o n r e q u i r e s the use o f p e s t i c i d e s , b u t i n t u r n , t h i s u s e b r i n g s about t h e p o s s i b i l i t y o f environmental p o l l u t i o n . Environmental hazards caused by c o n v e n t i o n a l a g r i c u l t u r a l chemicals a r e c l a s s i f i e d i n t o two c a t e g o r i e s ; a. n o n - s e l e c t i v e t o x i c i t y ( p a r a t h i o n ) a n d b. c o n c e n t r a t i o n a n d a c c u m u l a t i o n o f t o x i c compounds i n t h e e n v i r o n ­ ment (DDT a n d BHC). P o l l u t i o n f r e e p e s t i c i d e s , t h e r e f o r e , s h o u l d have s e l e c t i v e t o x i c i t y t o t a r g e t o r g a n i s m s a n d b e s e n s i t i v e f o r p h o t o l y s i s a n d d e g r a d a t i o n b y s o i l m i c r o o r g a n i s m s . From t h e s e v i e w p o i n t s , a n t i b i o t i c s may b e presumed t o b e u s e f u l b i o d e g r a d a b l e pesticides. As i s t r u e f o r every s c i e n t i f i c technique, t h e use of a g r i c u l t u r a l a n t i b i o t i c s a l s o has i t s advantages and limitations. The a d v a n t a g e s . 1) S e l e c t i v e t o x i c i t y t o t a r g e t o r g a n i s m s : S i n c e most a n t i b i o t i c s have s e l e c t i v e t o x i c i t y t o t a r g e t organisms and l o w t o x i c i t y t o mammals a s shown i n T a b l e I I I , t h e y c a n b e s a f e l y u s e d w i t h o u t h a r m i n g man, l i v e s t o c k , f i s h a n d c r o p s . Mode o f a c t i o n o f a g r i c u l t u r a l a n t i b i o t i c s a r e summarized i n T a b l e ÏV. Table I I I . Antibiotic

T o x i c i t y o f a n t i b i o t i c s t o animals Animal

Acute o r a l t o x i c i t y ( L D o mg/kg) 5

Blasticidin S Kasugamycin Polyoxins Validamycin Tetranactin

Rat Mouse Mouse Mouse Mouse

53.3 20,900 15,000 10,000 15,000

PESTICIDE C H E M I S T R Y IN T H E 2 0 T H

186

Table IV.

Mode o f a c t i o n o f a n t i b i o t i c Primary action

Antibiotic

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch010

Polyoxins Tetranactin Validamycin Blasticidin S Kasugamycin Cycloheximide Streptomycin Cellocidin Griseofulvin

CENTURY

site

C h i t i n synthesis of c e l l w a l l C a t i o n leakage from m i t o c h o n d r i a Biosynthesis of i n o s i t o l

• Protein synthesis * -ι j

DNA s y n t h e s i s

2) E a s y d e g r a d a t i o n b y s o i l m i c r o o r g a n i s m s : A n t i b i o t i c s p r o d u c e d b y m i c r o o r g a n i s m s w o u l d be r a p i d l y d e g r a d e d b y s o i l microorganisms. A f t e r a p p l i c a t i o n t o the crop, a n t i b i o t i c s might be r a p i d l y b r o k e n down i n t h e e n v i r o n m e n t , so t h a t t h e r e may be no d a n g e r o f e n v i r o n m e n t a l p o l l u t i o n and f o o d c o n t a m i n a t i o n . 3) S m a l l amount o f compound u s e d i n a u n i t a r e a : S i n c e a g r i c u l t u r a l a n t i b i o t i c s a r e sprayed a t v e r y l o w c o n c e n t r a t i o n as shown i n T a b l e V, t h e amount o f compounds s p r a y e d i n a u n i t a r e a i s f a r l e s s (1/10 - 1/100) t h a n t h a t o f o t h e r c o n v e n t i o n a l p e s t i c i d a l c h e m i c a l s . A l s o a n t i b i o t i c s w o u l d be r a p i d l y d e g r a d e d by s o i l m i c r o o r g a n i s m s . T h e r e f o r e , i t i s expected t h a t the use of a g r i c u l t u r a l a n t i b i o t i c s does n o t b r i n g about t h e p o s s i b i l i t y o f environmental p o l l u t i o n . T a b l e V.

The c o n c e n t r a t i o n o f a n t i b i o t i c f o r a p p l i c a t i o n

Antibiotic Cycloheximide Blasticidin S Kasugamycin Validamycin Tetranactin Polyoxins Streptomycin [Other f u n g i c i d e s ] O r g a n i c p h o s p h o r u s compounds O r g a n i c s u l f u r compounds I n o r g a n i c s u l f u r compounds B o r d e a u x m i x t u r e (CuSO/,)

Concentration 2 10 20 30 100 100 100

- 3 - 20 - 40 - 50 - 130 - 200 - 200

500 1,000 - 1,500 2,000 4,000

(ppm)

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Antibiotics

187

4) M a n u f a c t u r e o f b i o - a c t i v e compounds w i t h c o m p l e x c h e m i c a l s t r u c t u r e s : N o v e l b i o - a c t i v e compounds w i t h v e r y c o m p l e x c h e m i c a l s t r u c t u r e s w h i c h a r e o u t s i d e t h e domain o f o r g a n i c s y n t h e s i s , c a n be i s o l a t e d a n d m a n u f a c t u r e d on a c o m m e r c i a l b a s i s . 5) F a v o r a b l e i n v e s t m e n t i n e q u i p m e n t : V a r i o u s a n t i b i o t i c s can be p r o d u c e d b y u s i n g a s i n g l e s e t o f e q u i p m e n t a n d f a c i l i t i e s . T h i s advantage b r i n g s about l o w i n i t i a l c o s t o f a n t i b i o t i c s .

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch010

6) U t i l i z a t i o n o f s o l a r e n e r g y : A n t i b i o t i c s a r e p r o d u c e d b y u t i l i z i n g a g r i c u l t u r a l products which are obtained from b i o l o g i c a l p h o t o s y n t h e t i c c o n v e r s i o n o f s o l a r e n e r g y . The p r o d u c t i o n o f a n t i b i o t i c s does n o t much consume t h e s t o r e d e n e r g y s u c h a s o i l and coal. The

limitations.

1) D i f f i c u l t y f o r a n a l y s i s i n m i c r o - s c a l e : A n t i b i o t i c s a r e g e n e r a l l y m i x t u r e s o f v a r i o u s s t r u c t u r a l l y r e l a t e d components l i k e polyoxins. This complexity i s a d i f f i c u l t y for analysis i n micros c a l e a n d s a f e t y e v a l u a t i o n o f compounds. 2) R e s i s t a n t o f p l a n t p a t h o g e n s t o a n t i b i o t i c s : T o l e r a n c e or r e s i s t a n c e o f p a t h o g e n i c microorganisms t o a n t i b i o t i c s has occurred shortly after application of a n t i b i o t i c s for the control o f p l a n t d i s e a s e s a s shown i n T a b l e V I . I n order t o reduce o r a v o i d t h e emergence o f t o l e r a n t f u n g i a n d b a c t e r i a i n t h e f i e l d s , the a l t e r n a t e o r combined a p p l i c a t i o n o f c h e m i c a l s w i t h d i f f e r e n t mechanisms o f a c t i o n i s recommended. Table VI. Antibiotic Blasticidin S Kasugamycin Polyoxins Streptomycin

Resistance to a n t i b i o t i c Where n o t e d Laboratory F i e l d and l a b . F i e l d and l a b , F i e l d and l a b .

Major organism Pyricularia Vyricularia Altemaria Xanthomonas

oryzae oryzae kikuchiana oryzae

P u b l i c h e a l t h a s p e c t s . A l i m i t e d number a n d a r e l a t i v e l y s m a l l q u a n t i t y o f m e d i c a l a n t i b i o t i c s have b e e n i n t r o d u c e d i n a g r i c u l t u r a l u s e a s shown i n T a b l e I . M o s t a g r i c u l t u r a l a n t i ­ b i o t i c s have been used o n l y f o r p l a n t p r o t e c t i o n purposes and n o t used i n m e d i c a l treatment. T h e r e f o r e , the p u b l i c ' s concern f o r t h e e n v i r o n m e n t a l p r o b l e m o f a n t i b i o t i c s must b e d i f f e r e n t i n t h e two a r e a s where a n t i b i o t i c s a r e u s e d . A g r i c u l t u r a l a n t i b i o t i c s do not i n v o l v e p r i m a r i l y the h e a l t h o f t h e i n d i v i d u a l , b u t t h e i r u s e has m a c r o e n v i r o n m e n t a l c o n s e q u e n c e s . M o s t human i n f e c t i o u s d i s e a s e s a r e caused by b a c t e r i a and v i r u s e s , w h i l e p l a n t pathogens

188

PESTICIDE C H E M I S T R Y IN T H E 2 0 T H C E N T U R Y

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch010

a r e m o s t l y c l a s s i f i e d a s f u n g i . A c c o r d i n g l y , most m e d i c a l a n t i ­ b i o t i c s a r e e f f e c t i v e a g a i n s t b a c t e r i a , whereas a g r i c u l t u r a l antibiotics aregenerally fungicidal. S e l e c t i v i t y of a g r i c u l t u r a l a n t i b i o t i c a c t i o n can eradicate fungi responsible f o r the target p l a n t d i s e a s e without harming other microorganisms such as b a c t e r i a p a r a s i t i c on humans. A p p l i c a t i o n o f a n t i b i o t i c s f o r the c o n t r o l o f p l a n t p e s t s i s never concerned i n t h e development of r e s i s t a n t microorganisms t o medical a n t i b i o t i c s . Some a n t i b i o t i c s c a n be s y n t h e s i z e d c h e m i c a l l y . I n t h i s respect there i s no d i f f e r e n c e b e t w e e n a n t i b i o t i c s a n d s y n t h e t i c c h e m i c a l s . The problem i s whether an a n t i b i o t i c i s used i n a g r i c u l t u r a l o r i n m e d i c a l use. I t makes no d i f f e r e n c e w h e t h e r i t i s p r o d u c e d b y microorganisms o r synthesized chemically. In t h i s a r t i c l e thepresent status o f a g r i c u l t u r a l a n t i ­ b i o t i c s h a s been d e s c r i b e d . T h e i r development i n Japan h a s b r o u g h t a b o u t s u c c e s s f u l d i s c o v e r i e s o f b l a s t i c i d i n S, k a s u g a m y c i n , p o l y o x i n s and v a l i d a m y c i n . R e c e n t l y , s t u d i e s on a g r i c u l t u r a l a n t i b i o t i c s have n o t been l i m i t e d o n l y t o c o n t r o l l i n g p l a n t p a t h o g e n i c m i c r o o r g a n i s m s , b u t e x t e n d e d w i d e r a n d more a c t i v e l y over the v a r i o u s s u b j e c t s such as u t i l i z a t i o n as a n t i v i r a l agents, i n s e c t i c i d e s , h e r b i c i d e s and p l a n t r e g u l a t o r s . I t i s expected t h a t many p o t e n t i a l a n t i b i o t i c s w i l l be d e v e l o p e d a n d a p p l i e d i n a g r i c u l t u r e i n t h e near f u t u r e .

Literature c i t e d (1) Dekker, J. "Fungicides" V o l . II, 579-635. Academic Press, New York (1969) (2) Dekker, J. (1971), World Rev. Pest. Control 10, 9-23. (3) Thirumalachar, M. J. (1968), Adv. Appl. Microbiol. 10, 313-337. (4) Woodbine, M. (ed.), " A n t i b i o t i c s in A g r i c u l t u r e " , Butterworths, London (1962). (5) Zaumeyer, W. J. " F i r s t International Conference on A n t i b i o t i c s in Agriculture" (National Academy of Sciences­ -National Research Council pub. 397), pp. 171-196. Washington (1956). (6) Woodcock, D. "Systemic Fungicides", pp. 42-54, Longman, London (1972). (7) Takeuchi, S., Hirayama, K., Ueda, K., Sakai, H., and Yonehara, H. (1958), J. Antibiot., 11A, 1-5. (8) Misato, T., Ishii, I., Asakawa, M., Okimoto, Y., and Fukunaga, K. (1959), Ann. Phytopath. Soc. Japan 24, 302-306. (9) Asakawa, Μ., Misato, T., and Fukunaga, K. (1963), Pesticide and Technique 8, 24-30. (10) Ō t a k e , N., Takeuchi, S., Endō, T., and Yonehara, H. (1966), Agr. Biol. Chem. 30, 132-141. (11) Yonehara, H., and Ō t a k e , Ν. (1966), Tetrahedron Letters, pp. 3785-3791.

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(12) Seto, H., Yamaguchi, I., Ōtake, Ν., and Yonehara, H. (1966), Tetrahedron Letters, pp. 3793-3799. (13) Seto, H., Yamaguchi, I., Ōtake, Ν . , and Yonehara, H. (1968), Agr. Biol. Chem. 32, 1292-1298. (14) Huang, K. T., Misato, T., and Asuyama, H. (1964), J. Antibiot. 17A, 65-74. (15) Misato, T., Ishii, I., Asakawa, M., Okimoto, Y., and Fukunaga, K. (1961), Ann. Phytopath. Soc. Japan 26, 19-24. (16) Misato, T., Okimoto, Y., Ishii, I., Asakawa, Μ., and Fukunaga, K. (1961), Ann. Phytopath. Soc. Japan 26, 25-30. (17) Coutsogeogopoulos, C. (1969), Fed. Proc. 28, 844. (18) Yukioka, M., Hatayama, T., and Morisawa, S. (1975), Biochim. Biophys. Acta 390, 192-208. (19) Hirai, T., and Shimomura, T. (1965), Phytopathology 55, 391-395. (20) Tanaka, N., Sakagami, Y., Yamaki, H., and Umezawa, H. (1961), J. Antibiot. 14A, 123-126. (21) Sugimoto, T. (1972), Nihon Noson Igakukai Zasshi 21, 316-317. (22) Yamaguchi, I., Takagi, K., and Misato, T. (1972), Agr. Biol. Chem. 36. 1719-1727. (23) Umezawa, H., Okami, Y., Hashimoto, T., Suhara, Y., Hamada, M., and Takeuchi, T. (1965), J. Antibiot. 18, 101-108. (24) Suhara, Y., Maeda, K., and Umezawa, H. (1966), Tetrahedron Letters, pp. 1239-1244. (25) Suhara, Y., Sasaki, F., Maeda, K., Umezawa, H., and Ohno, Μ., (1968), J. Am. Chem. Soc. 90, 6559-6560. (26) Ikekawa, T., Umezawa, H., and I i t a k a , Y. (1966), J. Antibiot. 19, 49-50. (27) Nakajima, M., Shibata, H., Kitahara, K., Takahashi, S., and Hasegawa, A. (1968), Tetrahedron Letters, pp. 2271-2274. (28) Kitahara, K., Takahashi, S., Shibata, H., Kurihara, Ν . , and Nakajima, M. (1969), Agr. Biol. Chem. 33, 748-754. (29) Ishiyama, T., Hara, I., Matsuoka, M., S a i t o , K., Shimada, S., Izawa, R . , Hashimoto, T., Hamada, Μ., Okami, Y., Takeuchi, T., and Umezawa, H. (1965), J. Antibiot. 18, 115-119. (30) Tanaka, Ν . , Yamaguchi, H., and Umezawa, H. (1966), J. Biochem. 60, 429-434. (31) Miura, H., I t o , H., and Takahashi, S. (1975), Ann. Phytopath. Soc. Japan 41, 415-417. (32) Suzuki, S., Isono, K., Nagatsu, J., Mizutani, T., Kawashima, Y., and Mizuno, T. (1965). J. Antibiot. 18A, 131. (33) Isono, K., Nagatsu, J., Kawashima, Y., and Suzuki, S. (1965), Agr. Biol. Chem. 29, 848-854. (34) Isono, K., and Suzuki, S. (1968), Tetrahedron Letters, pp. 1133-1137. (35) Sasaki, S., Ota, N., Eguchi, J., Furukawa, Y., Akashiba, T., Tsuchiyama, T., and Suzuki, S. (1968). Ann. Phytopath. Soc. Japan 34, 272-279. (36) Endo, Α., and Misato, T. (1969), Biochem. Biophys. Res. Commun. 37, 718-722.

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(37) Ohta, Ν . , K a k i k i , Κ., and Misato, T. (1970), Agr. Biol. Chem. 34, 1224-1234. (38) H o r i , Μ., K a k i k i , K., and Misato, T. (1974), Agr. Biol. Chem. 38, 691-698. (39) Isono, K., Asahi, K., and Suzuki, S. (1969), J. Am. Chem. Soc. 91, 7490-7505. (40) Isono, K., and Suzuki, S. (1968), Tetrahedron Letters, pp. 203-208. (41) Asahi, K., Sakurai, T., Isono, K., and Suzuki, S. (1968). Agr. Biol. Chem. 32, 1046-1047. (42) Kuzuhara, H., Ohrui, H., and Emoto, S. (1973), Tetrahedron Letters, pp. 5055-5058. (43) Eguchi, J., Sasaki, S., Ota, Ν . , Akashiba, T., Tsuchiyama, T., and Suzuki, S. (1968), Ann. Phytopath. Soc. Japan 34, 280-288. (44) Sasaki, S., Ohta, N., Yamaguchi, I., Kuroda, S., and Misato, T. (1968), J. Agr. Chem.Soc.Japan 42, 633-638. (45) Suzuki, S., Isono, K., Nagatsu, J., Kawashima, Y., Yamagata, K., Sakai, K., and Hashimoto, K. (1966), Agr. Biol. Chem. 30, 817-819. (46) Isono, K., Nagatsu, J., Kobinata, K., Sakai, K., and Suzuki, S. (1967), Agr. Biol. Chem. 31, 190-199. (47) Nishimura, M., Kohmoto, K., and Udagawa, H. (1973), Rept. Tottori Mycol. Inst. (Japan) 10, 677-686. (48) H o r i , Μ., Eguchi, J., K a k i k i , K., and Misato, T. (1974), J. Antibiot. 27, 260-266. (49) M i t a n i , Μ., and Inoue, Y. (1968), J. Antibiot. 21, 492-496. (50) Iwasa, T., Yamamoto, H., and Shibata, M. (1970), J. Antibiot. 23, 595-602. (51) Iwasa, T., Higashide, E., Yamamoto, H., and Shibata, M. (1971), J. Antibiot. 24, 107-113. (52) Iwasa, T., Kameda, Y., A s a i , M., Horii, S., and Mizuno, K . (1971), J. Antibiot. 24, 119-123. (53) Horii, S., and Kameda, Y. (1972), J. Chem.Soc.Comm., pp. 747-748. (54) Hosokawa, S., Ogiwara, S., and Murata, Y. (1974), J. Takeda Res. Lab. 33, 119-131. (55) H o r i i , S., Iwasa, T., and Kameda, Y. (1971), J. Antibiot. 24, 57-58. (56) H o r i i , S., Iwasa, Y., Mizuta, E., and Kameda, Y. (1971), J. Antibiot. 24, 59-63. (57) Kamiya, K., Wada, Y., Horii, S., and Nishikawa, M. (1971), J. Antibiot. 24, 317-318. (58) Wakae, O., and Matsuura, K. (1974), Proc. 1st Intersectional Congress of IAMS (Science Council of Japan) 3, 620-627. (59) Iwasa, T., Higashide, E., and Shibata, M. (1971), J. Antibiot. 24, 114-118. (60) Wakae, O., and Matsuura, K. (1973), Abstr. 2nd International Congress of Plant Pathology, No. 129 (U.S.A.)

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(61) Kameda, Y., and Horii, S. (1972), J. Chem. Soc. Comm., pp. 746-747. (62) Kameda, Y., and Yamamoto, K. (1970), Abstr. Ann. Phytopath. Soc. Japan 36, 356. (63) Takaoka, K., Kuwayama, T., and Aoki, A. (1971), Japanese Patent, 615332. (64) Sakata, K., Sakurai, Α., and Tamura, S. (1974), Agr. Biol. Chem. 38, 1883-1890. (65) Sakata, K., Sakurai, Α., and Tamura, S. (1974), Tetrahedron Letters, pp. 4327-4330. (66) Sakata, K., Sakurai, Α., and Tamura, S. (1975), Agr. Biol. Chem. 39, 885-892. (67) Sakata, K., Sakurai, Α., and Tamura, S. (1975), Tetrahedron Letters, pp. 3191-3194. (68) Suzuki, S., and Okuma, K. (1958), J. Antibiot. 11, 84-86. (69) Suzuki, S., Nakamura, G . , Okuma, K., and Tomiyama, Y. (1958), J. Antibiot. 11, 81-83. (70) Okimoto, Y., and Misato, T. (1963), Ann. Phytopath. Soc. Japan 28, 209-215. (71) Okimoto, Y., and Misato, T. (1963), Ann. Phytopath. Soc. Japan 28, 250-257. (72) Ando, Κ., O i s h i , H., Hirano, S., Okutomi, T., Suzuki, K., Okazaki, H., Sawada, Μ., and Sagawa, T. (1971), J. Antibiot. 24, 347-532. (73) Hirano, S., Sagawa, T., Takahashi, H., Tanaka, Ν . , O i s h i , H., Ando, K., and Togashi, K. (1973), J. Econ. Entomol. 66, 349-351. (74) Ando, K., Murakami, Y., and Nawata, Y. (1971), J. Antibiot. 24, 418-422. (75) I i t a k a , Y., Sakamaki, T., and Nawata, Y. (1972), Chemistry Letters, pp. 1225-1230. (76) Ando, K., Sagawa, T., O i s h i , H., Suzuki, K., and Nawata, Y. (1974), Proc. 1st Intersectional Congress of IAMS (Science Council of Japan) 3, 630-640. (77) Sagawa, T., Hirano, S., Takahashi, H., Tanaka, N., O i s h i , H., Ando, K., and Togashi, K. (1972), J. Econ. Entomol. 65, 372-375. (78) Yamada, O., Kaise, Y., Futatsuya, F., Ishida, S., I t o , K., Yamamoto, H., and Munakata, K. (1972), Agr. Biol. Chem. 36, 2013-2015. (79) Nishimura, H., K a t a g i r i , K., Sato, K., Mayama, Μ., and Shimaoka, N. (1956), J. Antibiot. 9A, 60-62. (80) Sobin, Β. Α., and Tanner, F. W. Jr. (1954), J. Am. Chem. Soc. 76, 4053. (81) Yamada, O., Ishida, S., Futatsuya, F., I t o , K., Yamamoto, H., and Munakata, K. (1974), Agr. Biol. Chem. 38, 1235-1240. (82) Ishida, S., Yamada, O., Futatsuya, F., I t o , K., Yamamoto, H., and Munakata, K. (1974), Proc. 1st Intersectional Congress of IAMS (Science Council of Japan) 3, 641-650.

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(83) Aizawa, S., Nakamura, Y., Shirato, S., Taguchi, R., Yamaguchi, I., and Misato, T. (1969). J. Antibiot. 22, 457-462. (84) Yamaguchi, I., Taguchi, R., Huang, K. T., and Misato, T. (1969), J. Antibiot. 22, 463-466.

11 Perspectives of Hormonal Control of Insect Development J. B. SIDDALL

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch011

Zoecon Research Laboratories, 975 California Ave., Palo Alto, Calif. 94304

In keeping with the symposium theme of p e s t i c i d e chemistry i n the Twentieth Century, t h i s paper will discuss chemical perspectives of i n s e c t development which have provided both a proven method of i n s e c t con­ trol and a number of promising avenues f o r f u r t h e r research i n t o new s t r a t e g i e s f o r s e l e c t i v e pest c o n t r o l . Bearing i n mind that another 24 years of Twentieth Century p e s t i c i d e chemistry are still untouched, it would seem appropriate at t h i s symposium to t r y to look ahead i n t o some areas of i n s e c t chemistry which remain to be explored. In so doing, it will be necessary to reexamine c o n t i n u a l l y whether such areas of research on chemical pest c o n t r o l will lead to s e l e c t i v i t y on the one hand f o r a l i m i t e d number of i n s e c t f a m i l i e s , or on the other hand f o r all i n s e c t s as a c l a s s with safety to higher animals. Because the hormonal regula­ tion of i n s e c t development i s so fundamentally d i f f e r e n t from that of higher animals, the l a t t e r kind of s e l e c t i v i t y has been inherent i n chemical p e s t i c i d e s which i n t e r f e r e with t h i s r e g u l a t i o n , and it would seem wise to continue the search f o r c l a s s s e l e c t i v e pesti­ cides of t h i s type. Among such avenues which are r e l a t i v e l y unexplored, are the c o n t r o l of molting i n l a r v a e , the mechanism of r e g u l a t i o n of molting hormone synthesis and s e c r e t i o n and the pathway of molting hormone b i o s y n t h e s i s . The mechanism of C-20 hydroxylation of α-ecdysone and the involvement of c o f a c t o r s remain unknown, even though t h i s i s a c r u c i a l step i n the genesis of the a c t i v e hormone ß-ecdysone. What is almost c e r t a i n i s that l a r v a l development without ecdysones would be impossible. It is likely that the higher centers controlling the timing and the rate of synthesis of the known hormones will exert t h e i r a c t i o n through small peptide neurohormones associated with complex p r o t e i n 197

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch011

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THE

20TH

CENTURY

c a r r i e r s , i n addition to e l e c t r i c a l control through direct innervation. Even the d i r e c t nervous c o n t r o l of e n d o c r i n e g l a n d s by e l e c t r i c a l means w i l l probably i n v o l v e c o n v e r s i o n of nervous impulses i n t o c h e m i c a l transmitters which i n h i b i t glandular activity. Although the a c c u m u l a t i o n f o r i s o l a t i o n and s t r u c t u r e elucida­ t i o n o f s u c h n e u r o h o r m o n e s and t r a n s m i t t e r s i s a formi­ d a b l e t a s k , the p o t e n t i a l f o r the use of such knowledge i n p e s t c o n t r o l i s s u r e l y no l e s s f o r m i d a b l e . With the f u t u r e i n m i n d i t i s t h i s w r i t e r ' s h o p e t o g a i n some perspectives o f i n s e c t d e v e l o p m e n t and i t s h o r m o n a l c o n t r o l as a g u i d e t o f u t u r e r e s e a r c h , by r e v i e w i n g a b r i e f s e l e c t i o n of events which have punctuated the spectacular development of hormonal p e s t i c i d e s as i n s e c t growth regulators. Hormone

Isolation

Between the d i s c o v e r y of i n s e c t j u v e n i l e hormone (JH) some f o r t y y e a r s a g o (1) a n d t h e b e g i n n i n g o f w o r k on c h e m i c a l s t r u c t u r e e l u c i d a t i o n , o v e r t w e n t y y e a r s e l a p s e d f o r t h e m a j o r r e a s o n t h a t t h e r e was simply no u s a b l e s o u r c e of the hormone u n t i l W i l l i a m s discovered a r i c h d e p o t i n the abdomens of male s i l k m o t h s (2^,3) i n w h i c h a b o u t 3 m i c r o g r a m s was apparently stored i n Γθ grams o f t i s s u e . Without c a r e f u l experimentation (3) i t was g e n e r a l l y assumed t h a t the u n s t a b l e hormone was protected i n a large quantity of o i l y l i p i d s present i n the abdomens. H o w e v e r , i n 1976 i t was discovered that the a c c e s s o r y sex glands of the male C e c r o p i a moths have t h e e x c l u s i v e a b i l i t y t o s e q u e s t e r JH (£) . Quite apart from the i m p l i c a t i o n s f o r the study of insect s e x u a l i t y , the possession of such knowledge of a c c e s s o r y g l a n d s t o r a g e i n 1956 would almost c e r t a i n l y have r e v o l u t i o n i z e d t h e t e d i o u s p r o c e s s o f JH i s o l a t i o n and p u r i f i c a t i o n w h i c h was not accomplished u n t i l 1966 (5_) . In connection w i t h the future i s o l a t i o n of the r a r e n e u r o h o r m o n e s o f i n s e c t s , o n e may usefully recall t h i s l o c a l i z a t i o n of JH. No d o u b t t h e s u r g i c a l i s o l a ­ t i o n o f a c c e s s o r y sex g l a n d s w o u l d h a v e b e e n much s i m p l e r as a p u r i f i c a t i o n scheme t h a n the numerous c o l u m n and gas c h r o m a t o g r a p h i c p r o c e d u r e s e m p l o y e d . Closely related to these events i n i t s implications was the discovery t h a t JH c o u l d be i s o l a t e d , a l b e i t i n minute q u a n t i t i e s , from i n v i t r o c u l t u r e s of the endo­ c r i n e o r g a n s (60 . Because c u l t u r e medium i s r e l a t i v e l y free of e x t r a c t a b l e organic i m p u r i t i e s , the higher s t a t e of p u r i t y of hormones o b t a i n e d through organ c u l t u r e by s o l v e n t e x t r a c t i o n o f the medium more t h a n compensates f o r the smaller q u a n t i t i e s obtainable.

11.

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Hormonal

199

Control

These s i m p l e c o n s i d e r a t i o n s l e dt o t h e d i s c o v e r y (7) o f JH I I I ( F i g u r e 1) b y c u l t u r e o f o r g a n s f r o m M a n c T u c a sexta and t o t h e e l u c i d a t i o n o f important elements o f hormone b i o s y n t h e s i s f r o m p r o p i o n a t e , acetate, and m e v a l o n a t e (8). I t seems l i k e l y therefore that the R'

Ε

R"

! I

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch011

Η R « R= R— R -

Me; Et; Et; Et;

R' = Me; R" = Me ( JH III) R' = Me; R" = Me (JH II) W = Et; R" = Me (JH I) W = Et; R" - Et (JH 0) Figure

1.

techniques o f organ and t i s s u e culture w i l l play a major r o l e i n t h e i s o l a t i o n o f workable q u a n t i t i e s o f i n s e c t neurohormones. The o r i g i n a l i s o l a t i o n o f m o l t i n g hormones f r o m i n s e c t s a n d c r a y f i s h was c e r ­ t a i n l y no l e s s l a b o r i o u s than work on JHs, and r e c e n t advances i n organ c u l t u r e o f p r o t h o r a c i c glands have been reported (9,10) . T h e s e a d v a n c e s n o t o n l y verify the o r i g i n a l hypothesis t h a t α-ecdysone i s s e c r e t e d b y prothoracic glands, b u t also provide an invaluable t o o l for t h e future i n v e s t i g a t i o n o f ecdysone b i o s y n t h e s i s . To d a t e , t h e d e f i n i t i v e c o n v e r s i o n o f c h o l e s t e r o l t o α-ecdysone b y t h e s e g l a n d s i n v i t r o h a s n o t y e t b e e n reported, and without such evidence neither t h e d e t a i l e d study o f ecdysone biosynthesis n o r i t s i n h i b i ­ t i o n by chemicals as p o t e n t i a l p e s t i c i d e s c a n be expected t o progress r a p i d l y . During t h e events leading t o t h e i s o l a t i o n o f JH I , a n o t a b l e p a p e r o f W. S . B o w e r s a n d c o - w o r k e r s (11) p r e d i c t e d most a c c u r a t e l y a l l t h e s t r u c t u r a l f e a t u r e s o f t h e n o w k n o w n J H s ( F i g u r e 1) w i t h t h e s o l e exception of t h e unprecedented e t h y l branches on t h e terpenoid chains o f JH I and I I . On e x a m i n i n g t h e b a s i s o f t h i s p r e d i c t i o n , i t seems t h a t Bowers c a r e f u l l y p i e c e d together small items o f information from t h e l i t e r a t u r e and t h e l a b o r a t o r y b e n c h e v e n t h o u g h none o f t h e s e taken alone would have s u f f i c e d t o e l u c i d a t e t h e s t r u c ­ t u r e o f n a t u r a l J H I , w h i c h was a c c o m p l i s h e d two y e a r s l a t e r i n 1967 b y R o l l e r a n d c o - w o r k e r s ( 5 ) . Both o f these publications o f discrete chemical structures with hormone a c t i v i t y u n d o u b t e d l y opened t h e d o o r t ot h e numerous c h e m i s t s whose s k i l l s l a yi n s y n t h e s i s and s t r u c t u r e o p t i m i z a t i o n f o r maximum b i o l o g i c a l activity. F r o m t h e s e e v e n t s o n e may c o n c l u d e t h a t t h e l o n g a n d h a r d l a b o r o f hormone i s o l a t i o n was c l e a r l y w o r t h w h i l e ,

200

PESTICIDE C H E M I S T R Y

IN T H E 2 0 T H

® EVOLUTION OF ALTOS ID .

LC

c ; n

1

AEDES EGYPTI RELATIVE

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch011

POTENCY

1.2

4.5x\ 5.2 14X1

74

3.8x1 283

8.6X

2430 ALTOSID Figure 2.

CENTURY

11.

siDDALL

Hormonal

201

Control

and t h a t t h e s k i l l f u l a p p l i c a t i o n o f new t e c h n i q u e s o f the past decade c o u l d shorten c o n s i d e r a b l y t h e i s o l a ­ t i o n o f new i n s e c t hormones a n d p h y s i o l o g i c a l l y active substances f o r research i npest control.

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch011

Juvenile

Hormone A n a l o g s

as

Insecticides

The p o s s i b i l i t y o f u s i n g i n s e c t h o r m o n e s a s i n s e c ­ t i c i d e s arose as a by-product o f studies o f insect p h y s i o l o g y i n 1956 and t h e concept i s a t t r i b u t e d t o W i l l i a m s (2,12) . I n c h e m i c a l t e r m s t h e d i s c o v e r y o f J H a c t i v i t y i n f a r n e s o l and f a r n e s a l from feces o f meal w o r m s b y t h e l a t e P. S c h m i a l e k , c o u l d b e r e g a r d e d a s t h e b e g i n n i n g o f J H a n a l o g c h e m i s t r y (13_) . A l t h o u g h i t soon became c l e a r t h a t f a r n e s o l was n o t i d e n t i c a l w i t h natural JH, the important fact of i t s possession of demonstrable JH a c t i v i t y p r o b a b l y formed t h e b a s i sf o r Bowers and c o - w o r k e r s (11) e l a b o r a t i o n o f ( E , E ) - 1 0 , 1 1 epoxymethylfarnesoate. From t h i s l a t t e r compound t h e r e has emerged a l a r g e c l a s s o f p o t e n t a n a l o g s , m o s t l y e s t e r s , w h i c h a r e b a s e d o n t h e 15 c a r b o n s k e l e t o n o f f a r n e s a n e , and these have been reviewed i n d e t a i l by Staal (14). S i n c e t h i s c l a s s o f compound c o n t a i n s t h e o n l y two c h e m i c a l s which have so f a r r e c e i v e d government approval f o r use as i n s e c t growth r e g u l a t o r s ( A l t o s i d o r m e t h o p r e n e , F i g u r e 2, a n d k i n o p r e n e , F i g u r e 3 ) , t h e i r d i s c o v e r y w i l l be examined i n more d e t a i l . The hypo­ t h e t i c a l e v o l u t i o n o f A l t o s i d from epoxymethylfarnesoate 1

Figure 3.

i s i l l u s t r a t e d s c h e m a t i c a l l y i n F i g u r e 2, where c u r v e d arrows i n d i c a t e molecular s t r u c t u r a l changes and t h e n e a r b y n o t a t i o n s s u c h a s 4.5X a n d 14X d e n o t e t h e i n c r e a s e s i n b i o l o g i c a l potency a s s o c i a t e d w i t h each change. By l a t e 1971 these changes h a d been r e p o r t e d (15) a s l e a d i n g t o a n i n c r e a s e i n r e l a t i v e p o t e n c y o f 1900 f o l d c o m p a r e d w i t h J H I I I ( F i g u r e 2, t o p ) , i n laboratory mosquito bioassay. More r e c e n t assay d a t a i n d i c a t e a n i n c r e a s e o f 2,430 t i m e s , r e s u l t i n g i n l a b o r ­ a t o r y a c t i v i t y s u f f i c i e n t t o prevent emergence o f a d u l t

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m o s q u i t o e s w i t h 0.1 p a r t s p e r b i l l i o n i n w a t e r . Of the s i x molecular changes i n F i g u r e 2 perhaps the most i m p o r t a n t a r e r e p l a c e m e n t o f t h e 10,11 e p o x i d e by a t e r t i a r y m e t h o x y l g r o u p and the i n t r o d u c t i o n o f a c o n ­ jugated d i e n o i c e s t e r system, both of which c o n t r i b u t e markedly to i n c r e a s e d s t a b i l i t y i n the f i e l d . Clearly, s e v e r a l hundred changes were e x p l o r e d d u r i n g this p r o c e s s o f s t r u c t u r e o p t i m i z a t i o n and s e v e r a l o f these have been r e p o r t e d i n d e t a i l (14_,16_) . The c h e m i c a l and b i o l o g i c a l p r o p e r t i e s of the geometrical isomers of a r e l a t e d e t h y l e s t e r have been r e p o r t e d (17_) a n d a g e n e r a l r u l e f o r t h i s c l a s s i s t h a t the 2E,4E i s o m e r ( a l l trans) i s the most b i o l o g i c a l l y a c t i v e of the four possible. S e v e r a l approaches t o t h e i r s y n t h e s i s have been e x p l o r e d (1β_,17^18_) b u t t h e m e t h o d o f c h o i c e i s a s t e r e o s e l e c t i v e s y n t h e s i s (19^) i n v o l v i n g t h e c o n d e n s a ­ tion of d i a l k y l 3-methylglutaconates w i t h 7-methoxyc i t r o n e l l a l , i n turn manufactured from the pinenes present i n o i l of turpentine. At t h i s p o i n t the h i s t o r y of the concept of hor­ m o n a l c o n t r o l o f i n s e c t s s h o u l d be r e c a l l e d , s i n c e t h e m a j o r r e a s o n s f o r t h e s e l e c t i o n o f JH as a r a t i o n a l l e a d f o r p e s t i c i d e d e s i g n were t h e b e l i e f s t h a t JH o c c u r r e d o n l y i n i n s e c t s and n o t i n o t h e r a n i m a l s . The i m p l i c a t i o n was t h a t JH w o u l d t h e r e f o r e be selectively a c t i v e i n i n s e c t s w i t h no s i g n i f i c a n t e f f e c t s on other forms of l i f e . I n t h e c a s e s o f JH a n a l o g s o f the farnesane skeleton, extensive studies of comparative t o x i c o l o g y have l a r g e l y v e r i f i e d these b e l i e f s . Toxic o l o g i c a l r e s u l t s have been reviewed i n detail (20_) and a comprehensive study of the environmental f a t e and m e t a b o l i s m o f m e t h o p r e n e h a s b e e n c o m p l e t e d (21) . I n m o v i n g t o o t h e r c l a s s e s o f JH a n a l o g s , major departures from the farnesane s k e l e t o n have been reported i n the form of phenyl ethers (2j^23_,2£) , c y c l o hexenes s u c h as j u v a b i o n e (25_) , a n d s m a l l p e p t i d e s (26) as an e x t r e m e c a s e o f c o m p l e t e l y s e l e c t i v e a c t i o n on one f a m i l y o f b u g s . The l a t t e r c o m p o u n d s a r e m o s t remarkable f o r the pronounced d i f f e r e n t i a l a c t i v i t y of t h e i r o p t i c a l e n a n t i o m e r s , i n w h i c h one a n t i p o d e i s s e v e r a l t h o u s a n d times more a c t i v e b i o l o g i c a l l y t h a n the other (21). In connection w i t h the p e p t i d e s , i t s h o u l d be n o t e d t h a t t h e r e i s no f o r m a l p r o o f that t h e s e compounds e x e r t t h e i r a c t i o n as t r u e m i m i c s o f j u v e n i l e hormones a t the t a r g e t t i s s u e l e v e l . One may w e l l a s k w h e t h e r t h e s e p e p t i d e s a c t d i r e c t l y on the c o r p o r a a l l a t a g l a n d s as allatotropins.

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Studies o f thebiosynthesis o f the unique e t h y l branched JH a r e important n o t merely f o r t h e sake o f gaining knowledge, b u t f o r t h e major reason that a d e t a i l e d knowledge o f t h e pathway should a s s i s t i n t h e d e s i g n o f i r r e v e r s i b l e i n h i b i t o r s a s new i n s e c t c o n t r o l agents. Despite t h e major d i f f i c u l t i e s o f work w i t h nanogram q u a n t i t i e s o f m a t e r i a l s produced by organs o f fluctuating synthetic capacity, considerable progress has b e e n made s i n c e t h e i n t r o d u c t i o n o f o r g a n c u l t u r e techniques as a t o o l . I n 1970 t h i s a u t h o r wrote t h a t " a d v a n c e s i n o r g a n c u l t u r e t e c h n i q u e may l a t e r s i m p l i f y such work and p r e s e n t l y provide an avenue f o r f r u i t f u l research" (28_) . B y 1 9 7 3 t h e u s e o f i n v i t r o cultures l e d t o t h e e l u c i d a t i o n b y S c h o o l e y a n d c o - w o r k e r s (8_) o f the r o l e o f propionate as a precursor o f the e t h y l branches, and c u r r e n t work i n s e v e r a l l a b o r a t o r i e s i s d i v i d e d between whole organ c u l t u r e systems and homogenate s y s t e m s s u m m a r i z e d m o s t r e c e n t l y i n a com­ p r e h e n s i v e b o o k e n t i t l e d " T h e J u v e n i l e H o r m o n e s " (29^) . At t h e present time t h e candidacy o f homomevalonic a c i d as a p r e c u r s o r o f J H I a n d J H I I i s s t i l l a t t r a c t i v e even t h o u g h t h i s compound h a s n e v e r been i s o l a t e d f r o m any l i v i n g s y s t e m . In l o o k i n g ahead t o f u t u r e methods o f i n s e c t con­ t r o l b a s e d o n b i o s y n t h e t i c i n h i b i t i o n , i t w o u l d seem t h a t a few y e a r s o f hard work w i l l be n e c e s s a r y t o elucidate t h e i n d i v i d u a l steps o f t h e pathways, as a basis for synthesis of substrate analog inhibitors. These i n h i b i t o r s would be c l a s s i f i e d as a n t i - j u v e n i l e hormones a n d c o u l d b e e x p e c t e d t o show s e l e c t i v e a c t i o n on i n s e c t s a s a c l a s s . Such a n a l o g s a r e b y no means j u s t around t h e corner since a t l e a s t two important p r o p e r t i e s t h a t t h e y s h o u l d p o s s e s s may b e d i f f i c u l t t o build into small organic molecules suitable for pest control. These p r o p e r t i e s a r e t h e a b i l i t y t o withstand general metabolic inactivation while retaining the a b i l i t y t o i n h i b i t i r r e v e r s i b l y t h e t a r g e t enzymes o f the corpus a l l a t u m and t h e property t o accumulate s e l e c ­ t i v e l y i ncorpora a l l a t a , a p h y s i c a l l y small target, so as t o o f f s e t d i l u t i o n i n t h e g e n e r a l b o d y c a v i t y . Anti-juvenile

Hormones

Despite t h e t e s t i n g o f several thousand JH analogs i n many l a b o r a t o r i e s b e t w e e n 1 9 6 1 a n d 1975, no con­ firmed report o f JH antagonism appeared. P a r t o ft h e r e a s o n f o r t h i s may w e l l h a v e b e e n t h e u s e o f i n a p p r o ­ p r i a t e bioassays, such as t h e c l a s s i c a l Tenebrio t e s t o r

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G a l l e r i a wax wound a s s a y ; however, s e v e r a l l a b o r a t o r i e s maintained lengthier bioassays using early larval i n s t a r s i n which J H - a n t a g o n i s t i c a c t i v i t y would most l i k e l y be detected. The e x p e c t e d symptoms o f a n t i - J H a c t i v i t y i na t e s t chemical would be s i m i l a r t o those caused by s u r g i c a l removal (allatectomy) o f t h e corpora a l l a t a glands, which leads t o premature metamorphosis o f e a r l y stage l a r v a e i n t o pupae. Although t h e expression o f p r e m a t u r e m e t a m o r p h o s i s a t t h e t i m e o f a m o l t may l a g behind allatectomy by s e v e r a l days o r by an i n t e r v e n i n g l a r v a l i n s t a r , t h esurgery u s u a l l y shortens t h e feeding stages o f t h el a r v a e o f moths a n d b e e t l e s , which a r e the damaging stages o f the major pests o f crops. The s e a r c h f o r d e f i n e d c h e m i c a l s t r u c t u r e s w h i c h w i l l d u p l i c a t e t h ee f f e c t s o f s u r g i c a l a l l a t e c t o m y w i l l most l i k e l y c o n t i n u e a n d i n t e n s i f y i nt h enext few y e a r s , b u t i no r d e r f o r t h es e a r c h t o be o f a n y p r a c t i ­ c a l v a l u e i t must focus upon t h e holometabolous i n s e c t s which a r ethe major p e s t s o f a g r i c u l t u r e a n d the major insect vectors of disease. From the p r a c t i c a l view­ p o i n t , t h e r e c e n t d i s c o v e r y b y W. S . B o w e r s ( 3 0 ) t h a t the bedding p l a n t Ageratum houstonianum contains two chemicals which possess anti-JH a c t i v i t y on milkweed bugs b u tn o to n l a r v a e o f moths o r b e e t l e s , i s b o t h i n t r i g u i n g a n d d i s a p p o i n t i n g . Both c h e m i c a l s showed a very narrow spectrum o f a c t i v i t y on l a r v a e , and t h e more p o t e n t named p r e c o c e n e - 2 ( F i g u r e 4) p r o d u c e d e f f e c t s which could be counteracted by JH I I I (31).

Figure 4.

Precocene 2

Consequently, i t w i l l be important f o r future research to examine a t l e a s t two a s p e c t s o f t h i s work; t o e l u c i ­ date the mechanism o f a c t i o n o f precocenes on l a r v a e o f bugs, a n d t o f i n d w h e t h e r t h er e p o r t e d s t e r i l i z a t i o n o f a d u l t female i n s e c t s a n d t h er e p o r t e d indue t i o n o f d i a p a u s e i n C o l o r a d o p o t a t o b e e t l e s (31) i n v o l v e a s i m i l a r mechanism o f a c t i o n .

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Control

In c o n t r a s t with t h e present l i m i t e d range o f a p p l i c a t i o n s f o r i n s e c t growth regulators with JH a c t i v i t y , Bowers s t a t e s t h a t "a hormone a n t a g o n i s t o r anti-hormone w o u l d be a more e f f i c a c i o u s i n s e c t i c i d e " (31). This statement i sbased on t h e i d e a t h a t JHi s necessary throughout most stages o f i n s e c t l i f e , and the e x p e c t a t i o n t h a t an a n t i - J H which tends t o reduce the i n s e c t ' s JH l e v e l would be able t o a c ton t h e i n s e c t throughout most stages o f i t s l i f e w i t h t h e r e s u l t o f d i s r u p t i o n o f development. These o v e r s i m p l i ­ f i e d ideas would lead t o t h e b r i g h t prospect o f an a n t i - J H i n s e c t i c i d e which c o u l d be used t o c o n t r o l most l a r v a l stages o f i n s e c t s . However, these ideas over­ look two v i t a l l y important f a c t o r s . The d e v e l o p m e n t a l stage w h i c h w i l l emerge a t t h e m o l t from a g i v e n larval instar i sdecided only during a b r i e f c r i t i c a l period in t h e e a r l y part o f that i n s t a r , and t h e d e c i s i o n o r d e t e r m i n a t i o n f o r what w i l l emerge a s t h e n e x t stage depends on whether t h e b i o l o g i c a l l y e f f e c t i v e t i t e r o f JH i s above o r b e l o w a c r i t i c a l l e v e l d u r i n g t h e b r i e f critical period. Thus f o r n o r m a l development i n v o l v i n g f i v e l a r v a l i n s t a r s there would be f i v e critical p e r i o d s , four o f which could be i n f l u e n c e d by chemical reduction o f JH t i t e r t o d i s r u p t development. I ti s not y e t u n d e r s t o o d why t h r e e J H s a r e p r e s e n t d u r i n g c e r t a i n s t a g e s o f l a r v a l d e v e l o p m e n t , n o r i s i t known w h e t h e r the r a t i o s o f t h e hormones a r e important i n t h e d e t e r ­ mination o f t h e next molt. The very presence o f three hormones h a v i n g d i f f e r e n t morphogenetic potencies suggests a b u f f e r system which s t a b i l i z e s t h e b i o l o g i ­ c a l l y e f f e c t i v e l e v e l o f J H . The e f f e c t i v e l e v e l o f J H may prove t o be o n l y t h e p o r t i o n which i sbound t o hypothetical target t i s s u e receptors and n o t t h e p o r t i o n s bound t o c a r r i e r p r o t e i n o r i n f r e e c i r c u l a ­ t i o n , though each l e v e l w i l l i n f l u e n c e t h e others and a l l w i l l c o n t r i b u t e t o whole body t i t e r s measured by recently a v a i l a b l e techniques (32 33,3£) . /

There emerges a very complex p i c t u r e o f t h r e e hor­ mones s y n t h e s i z e d a n d s e c r e t e d a t v a r i a b l e r a t e s , com­ p e t i n g f o r c a r r i e r b i n d i n g p r o t e i n s , presumed r e c e p t o r proteins, epoxide hydratase and carboxyl esterase enzymes (35,36). I t i spossible experimentally t o measure t E ê t i m i n g o f c r i t i c a l p e r i o d s f o r l a r v a l d e ­ t e r m i n a t i o n and t o measure t o t a l l e v e l s o f JH a t these c r i t i c a l periods although both measurements i n v o l v e extreme d i f f i c u l t y * Approaches t o t h i s were d e s c r i b e d r e c e n t l y b y G . B . S t a a l (3JJ u s i n g t h i r d i n s t a r l a r v a e of t h e t o b a c c o hornworm moth, Manduca s e x t a , which were allatectomized and r a i s e d on JH impregnated d i e t s as an e x p e r i m e n t a l l y r e p r o d u c i b l e m e t h o d o f J H t h e r a p y .

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f

One s t r i k i n g r e s u l t o f S t a a l s w o r k was t h e v e r y l o w m o r p h o g e n e t i c p o t e n c y o f JH I I I r e l a t i v e t o JH I o r I I , measured as the a b i l i t y t o m a i n t a i n normal larval-larval molting i n the allatectomized insects. S i n c e t h e e f f e c t s o f p r e c o c e n e - 2 c a n be a b o l i s h e d b y a d d i t i o n o f J H I I I ( 3 1 ) , i t may t u r n o u t t h a t t h e p r e c o c e n e s a r e s e l e c t i v e a n t a g o n i s t s f o r JH I I I b u t n o t f o r t h e more p o t e n t JH I and I I . I f s o , t h e n a r r o w s p e c t r u m o f a c t i v i t y o f p r e c o c e n e - 2 may b e f u r t h e r l i m i t e d to those insects which lack the a b i l i t y to b i o s y n t h e s i z e JH I o r JH I I . The p r e s e n c e o f JH I has been r e p o r t e d i n l a r v a l cockroaches which are v e r y p r i m i t i v e i n s e c t s (3<8) . Work i n t h i s l a b o r a t o r y t o be r e p o r t e d i n d e t a i l e l s e w h e r e (39) f a i l e d t o d e t e c t a n y a c t i v i t y w h a t s o e v e r o f p r e c o c e n e - 2 on nymphs o f t h e cockroach, B l a t t e l l a germanica, or Schistocerca vaga, o r l a r v a e o f Aedes a e g y p t i m o s q u i t o e s , o r o f the bug P y r r h o c o r i s apterus which i s most s u r p r i s i n g i n view of i t s c l o s e r r e l a t i o n s h i p t o the milkweed bug. Similarly no e f f e c t s on l a r v a l d e v e l o p m e n t o r on egg m a t u r a t i o n i n Manduca s e x t a c o u l d be f o u n d . However, precocene-2 was r e p o r t e d (31) t o i n d u c e d i a p a u s e b e h a v i o r i n a d u l t Colorado p o t a t o b e e t l e s which were i n d e p e n d e n t l y found (40) t o c o n t a i n J H I I I a s t h e o n l y h o r m o n e p r e s e n t (280 picogram/animal). A d u l t f e m a l e s o f M a n d u c a s e x t a how­ e v e r c o n t a i n J H I I (3£,40_) a n d t r a c e s o f J H Ï ( 3 4 ) a n d are i n s e n s i t i v e to the action of precocene-2. Although corpora a l l a t a of the grasshopper S c h i s t o c e r c a vaga w e r e f o u n d (4jL) t o s y n t h e s i z e o n l y J H I I I i n _ v i t r o , t h e hormones p r e s e n t i n l a r v a e (which are i n s e n s i t i v e t o precocene-2) have n o t been i n v e s t i g a t e d . The analytical measurement o f which hormones o c c u r a t what l e v e l s i n l a r v a e o f v a r i o u s f a m i l i e s o f i n s e c t s assumes added i m p o r t a n c e even though i t r e m a i n s t o be seen w h e t h e r p r e c o c e n e s a c t by c h a n g i n g t h e c i r c u l a t i n g t i t e r o f JHs. The n e g a t i v e i m p l i c a t i o n s f o r p e s t c o n t r o l by p r e ­ c o c e n e s t h e m s e l v e s a r e c l e a r , b u t i t r e m a i n s t o be s e e n whether the expansion of t h e i r spectrum of a c t i v i t y i s l i m i t e d m e r e l y by t h e c h e m i c a l s t r u c t u r a l f e a t u r e s o f p r e c o c e n e s o r , more p r o b l e m a t i c a l l y , by t h e hormonal mechanisms which c o n t r o l i n s e c t development. In either c a s e t h e JH a n t a g o n i s t approach t o the c o n t r o l o f l a r v a l i n s e c t p e s t s p r e s e n t s a major c h a l l e n g e t o c h e m i c a l and physiological research.

Literature 1.

Cited

W i g g l e s w o r t h , V.B., (1934), 77, 191.

Q u a r t . J. M i c r o s c o p .

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W i l l i a m s , C.M., Nature (1956), 178, 212. W i l l i a m s , C.M., Biol. Bull. (1963), 124, 355. S h i r k , P.D., Dahm, K.H., and Röller, Η., Z. Natur­ forsch. C. (1976), 11, 199. 5. Röller, Η., Dahm, K.H., Sweeley, C.C., and T r o s t , B.M., Angew. Chem. (1967), 79, 190. Angew. Chem. I n t . E d . (1967), 6, 179. 6. Röller, Η., and Dahm, K.H., N a t u r w i s s e n s c h a f t e n (1970), 57, 454. 7. Judy, K.J., S c h o o l e y , D.A., Hall, M.S., B e r g o t , B.J., and Siddall, J.B., P r o c . N a t . Acad. Sci. USA (1973), 70, 1509. 8. S c h o o l e y , D.A., Judy, K.J., B e r g o t , B.J., Hall, M.S., and Siddall, J.B., P r o c . Nat. Acad. Sci. USA (1973), 70, 2921. 9. K i n g , D.S., B o l l e n b a c h e r , W.E., B o r s t , D.W., V e d e c k i s , W.V., O'Connor, J.D., I t t y c h e r i a h , P.I., and Gilbert, L . I . , P r o c . N a t . Acad. Sci. USA (1974), 71, 793. 10. C h i n o , H., S a k u r a i , S., O h t a k i , T., Ikekawa, Ν . , M i y a z a k i , Η., I s h i b a s h i , Μ., and A b u k i , Η., S c i e n c e (1974), 183, 529. 11. Bowers, W.S., Thompson, M.J., and E u b e l , E.C., Life Sci. (1965), 4, 2323. 12. W i l l i a m s , C.M., Scientific American (1967), 217 (1), 13. 13. Schmialek, P., Z. N a t u r f o r s c h . B. (1961), 16, 461. 14. S t a a l , G.B., Annu. Rev. Entomol. (1975), 20, 417460. 15. Chem. Eng. News. (1971), 49 (49), 33. 16. H e n r i c k , C.A., S t a a l , G.B., and Siddall, J.B., J. Agr. Food Chem. (1973), 21, 354. 17. H e n r i c k , C.A., Willy, W.E., G a r c i a , B.A., and S t a a l , G.B., J. A g r . Food Chem. (1975), 23, 396. 18. H e n r i c k , C.A., Willy, W.E., McKean, D.R., Baggiolini, Ε., and Siddall, J.B., J. O r g . Chem. (1975), 40, 8. 19. H e n r i c k , C.A., Willy, W.E., Baum, J.W., Baer, T.A., G a r c i a , B.A., M a s t r e , T.A., and Chang, S.M., J. Org. Chem. (1975), 40, 1. 20. S i d d a l l , J.B., E n v i r o n . H e a l t h P e r s p e c . (1976) 14, 119-126. 21. Idem., I b i d . , r e f e r e n c e s 20-31 t h e r e i n . 22. Bowers, W.S., S c i e n c e (1969), 164, 323. 23. P a l l o s , F.M., Menn, J.J., L e t c h w o r t h , P.E., Miaullis, J.B., Nature (1971), 232, 486. 24. H a n g a r t n e r , W., Suchý, Μ., Wipf, H.K., and Z u r f l u e h , R., J. A g r . Food Chem. (1976), 24, 169. 25. Bowers, W.S., F a l e s , H.M., Thompson, M.J., U e b e l , E.C., S c i e n c e (1966), 154, 1020.

208 26.

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31. 32. 33. 34. 35.

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PESTICIDE CHEMISTRY IN THE 20TH CENTURY H l a v a c e k , J . , Poduska, K., Sorm, F., and Slama, Κ., Collect. Czech. Chem. Commun. (1976), 41, 1257 and references therein. Poduska, Κ., Sorm, F., and Slama, Κ., Z. Natur­ forsch. B. (1971), 26, 719. S i d d a l l , J.B., i n "Chemical E c o l o g y , " Ed: E. Sondheimer and J.B. Simeone, page 289. Acad. P r e s s , New York, N.Y., 1970. "The J u v e n i l e Hormones," Ed: L.I. Gilbert; Plenum P r e s s , New York, N.Y., 1976. Bowers, W.S., i n "The J u v e n i l e Hormones," page 397. Ed: L . I . Gilbert; Plenum P r e s s , New York, NY (1976). Bowers, W.S., S c i e n c e (1976), 193, 542. Dunham, L.L., S c h o o l e y , D.A., and Siddall, J.B., J. Chromat. Sci. (1975), 13, 334. B e r g o t , B . J . , S c h o o l e y , D.A., C h i p p e n d a l e , G.M., and Y i n , C-M., L i f e Sci. (1976), 18, 811. P e t e r , M.G., Dahm, K.H., and Röller, Η., Z. N a t u r f o r s c h C. (1976), 31, 129. Kramer, K.J., Dunn, P.E., P e t e r s o n , R.C., and Law, J.H., i n "The J u v e n i l e Hormones," page 327. Ed.: L.I. Gilbert; Plenum P r e s s , New York, NY (1976). S l a d e , Μ., and Zibitt, C.H., P r o c . I I I n t . IUPAC Congr. P e s t . Chem. (1971), 3, 45. S t a a l , G.B., p r e s e n t e d a t the I n t e r n a t i o n a l JH Symposium, Lake Geneva, Wisc. USA; Nov. 10, 1975. L a n z r e i n , Β., Hashimoto, M., Parmakovich, V., N a k a n i s h i , K., Wilhelm, R., and Lüscher, Μ., L i f e Sci. (1975), 16, 1271. S t a a l , G.B., C e r f , D.A., and L u d v i k , G., M a n u s c r i p t in p r e p a r a t i o n (1976). P e t e r , M.G., B i e s s e l s , H.W.A., Seshan, K.R., Röller, H., Bhaskaran, G., and Dahm, K.H. (1976), Abs. P a p e r s , 172nd Amer. Chem. Soc. Mtg. P e s t . D i v . No. 040. Judy, K.J., S c h o o l e y , D.A., H a l l , M.S., Bergot, B . J . , and Siddall, J.B., Life Sci. (1973), 13, 1511.

12 Insect Pheromones MURRAY S. BLUM

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch012

Department of Entomology, University of Georgia, Athens, Ga. 30602

That exocrinological chemistry is a r e l a t i v e l y neoteric field i s indicated by the fact that the first insect pheromone was identified only fifteen years ago (1). Since that time, chemical releasers of insect behavior have been characterized at a dizzying rate, and investigations of both the chemistry and func­ tions of these compounds have become commonplace in laboratories all over the world. Pheromonally speaking, we have gone from "rags to riches," but our comprehension of the modus operandi of these compounds is far from adequate, and the u t i l i z a t i o n of pheromones in pest management has only recently shown indications of being economically feasible (2). If chemical studies of pheromones have considerably outstripped the complementary behavioral investigations, they have nevertheless made it possible to analyze many of the nuances of insect behavior in ways never before possible. This chemical-behavioral interface promises to have major implications in f i e l d s as patently diverse as stereo­ chemistry and ecology. As a prerequisite to adumbrating the significant chemical discoveries relating to insect pheromones, it w i l l be necessary to exercise considerable s e l e c t i v i t y , and, unfortunately, exclude many contributions. However, several excellent reviews treating specific aspects of this f i e l d are available (3, 4, 5, 6, 7, 8, 9), and the reader is invited to consult these for appropriate background material. Evolution of Exocrinological Chemistry Identification of the structure of the sex attractant of the silkworm, Bombyx mori, by Butenandt et al. (1) must be regarded as a landmark in the field of the chemistry of insect signaling compounds. Characterization of the sex pheromone, bombykol, as (E,Z)-10,12-hexadecadien-1-ol was p a r t i c u l a r l y s i g n i f i c a n t , since this compound bears the main structural features of most of the sex pheromones subsequently identified from female 209

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Lepidoptera. Bombykol, representing an unsaturated normal a l c o h o l , i s t y p i c a l of a l l but a few moth sex pheromones i n being a medium-chain length compound with s i t e s of unsaturation and a terminal p o l a r group. Since t h i s theme recurs so f r e q u e n t l y i n moth sex pheromones, i t appears that these chemical r e l e a s e r s have been evolved independently i n several u n r e l a t e d l i n e s of moths (10). However, whereas the silkworm female appears to a t t r a c t males with a s i n g l e sex pheromone, many other i n s e c t s use blends of pheromones as chemical r e l e a s e r s of behavior. This phenomenon i s s t r i k i n g l y i l l u s t r a t e d i n the case of males of the bark b e e t l e Ips paraconfusus (=Ips confusus) which u t i l i z e three monoterpene a l c o h o l s as an aggregation pheromone ( 1 1 ) . Maximum a t t r a c t i o n of beetles i n the f i e l d was e x h i b i t e d i n the presence of a mixture of a l l three compounds, whereas s i n g l e or p a i r s of compounds were c o n s i d e r a b l y l e s s a c t i v e (12). S i m i l a r l y , i n l a b o r a t o r y b i o a s s a y s , mixtures of compounds were v a s t l y s u p e r i o r to s i n g l e c o n s t i t u e n t s as a t t r a c t a n t s (13). Whereas these terpene a l c o h o l s were s t r o n g l y s y n e r g i s t i c f o r L paraconfusus, they were i n h i b i t o r y f o r a second IJJS_ species which was a t t r a c t e d to a binary mixture but not to the normal t e r t i a r y mixture (13_). Furthermore, predators of l_. paraconfusus u t i l i z e d the pheromonal blend as a beacon to l o c a t e the bark b e e t l e s i n the trees (12). In t h i s case the h i g h l y adaptive aggregation pheromone c o n s t i t u t e d an e v o l u t i o n a r y boomerang. The r e s u l t of t h i s research on Ips was p a r t i c u l a r l y s i g n i f i c a n t , s i n c e i t emphasized that pheromones could be composed of blends of compounds t h a t acted i n t r a - and i n t e r s p e c i f i c a l l y as e i t h e r i n h i b i t o r s or a t t r a c t a n t s . U l t i m a t e l y I_. paraconfusus served as a seminal paradigm f o r the c o n c l u s i o n t h a t the s p e c i f i c i t y i s the blend (14). A major development i n the i d e n t i f i c a t i o n of many l e p i d o p terous sex pheromones was the use of a n e u r o p h y s i o l o g i c a l assay to d e t e c t both the p o l a r f u n c t i o n a l i t y as w e l l as the geometry and l o c a t i o n of the double bonds i n the molecule. This method, which measures the electroantennogram (EAG) response of the male antennae, takes advantage of the f a c t that the sex a t t r a c t a n t chemoreceptors d i s p l a y maximum s e n s i t i v i t y to compounds t h a t are s t r u c t u r a l l y c l o s e s t to the natural sex pheromone (10, 15). Even when a sex pheromone possesses two s i t e s of u n s a t u r a t i o n , the EAG w i l l a c c u r a t e l y monitor the l o c a t i o n of only one double bond, provided that i t i s present i n a homologue which possesses the a p p r o p r i a t e geometry. Testimony to the value of the EAG method was provided by the i d e n t i f i c a t i o n of ( J E , E j - 8 , 1 0 - d o d e c a d i e n - l - o l as the sex a t t r a c t a n t of the c o d l i n g moth Laspeyresia pomonella (16). Employing conventional chemical techniques, McDonough et al_. (Γ7) had reported t h a t ( Z , £ ) - 7 - m e t h y l - 3 - p r o p y l - 2 , 6 d e c a d i e n - l - o l was one of the major pheromones produced by females ° f k- pomonella, but t h i s c l a i m was subsequently withdrawn ( 1 8 ) . U l t i m a t e l y , employing gas chromatography-mass spectrometry,

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Beroza et al_. (19) i d e n t i f i e d (E_,E)-8,10-dodecadien-l-ol i n e x t r a c t s of female abdominal t i p s of the c o d l i n g moth. The c r i t i c a l importance of both concentration and mixtures of geometric isomers of sex pheromones was i l l u m i n a t e d i n an i n v e s t i g a t i o n of the responses of three species of male moths to the same sex pheromone, ( Z ) - 1 1 - t e t r a d e c e n y l acetate (20). A t t r a c t i o n of males of the European corn b o r e r , O s t r i n i a n u b i l a l i s , decreased as the c o n c e n t r a t i o n of the acetate was i n c r e a s e d , whereas the opposite e f f e c t r e s u l t e d w i t h males of the o b l i q u e banded l e a f r o l l e r . On the other hand, males of the redbanded l e a f r o l l e r , Argyrotaenia v e l u t i n a n a , responded uniformly to a l l concentrations of ( Z ) - 1 1 - t e t r a d e c e n y l a c e t a t e . Furthermore, i t was demonstrated t h a t males of the smartweed b o r e r , O s t r i n i a obumbratalis, were a t t r a c t e d to a 1:1 mixture of the ( E ) - and (Z)-isomers of t h i s e s t e r , but were unresponsive to 1:2 and 2:1 r a t i o s of the isomers of t h i s compound. These r e s u l t s c l e a r l y emphasize the a b i l i t i e s of male moths to s e l e c t i v e l y respond to sex pheromones based on e i t h e r the concentration of s i n g l e pheromones or pheromonal blends c o n t a i n i n g both geometric isomers of a compound. When viewed as a s p e c i e s - i s o l a t i n g mechanism, the i m p l i c a t i o n s of a response spectrum predicated on great o l f a c t o r y s e n s i t i v i t y to pheromonal concentration are c o n s i d e r a b l e . The a b i l i t y of male moths to perceive mixtures of geometric isomers with e x t r a o r d i n a r y a c u i t y was f u r t h e r documented i n an i n v e s t i g a t i o n of the responses of males of the redbanded l e a f r o l l e r and two populations of the European cornborer to isomers of 11-tetradecenyl acetate (21). Redbanded l e a f r o l l e r males were e s s e n t i a l l y unresponsive to pure preparations of t h e i r reported sex pheromone, ( Z ) - 1 1 - t e t r a d e c e n y l a c e t a t e , but were s t r o n g l y a t t r a c t e d to l u r e s c o n t a i n i n g up to 8% of the (E)-isomer. S i m i l a r l y , European cornborer males from Iowa responded maximally when 4% of the (E)-isomer was added to the ( Z ) - i s o m e r , whereas the New York population was a t t r a c t e d to an isomeric mixture c o n t a i n i n g about 4% of the (Z)-isomer. Enhanced a t t r a c t i o n by a small proportion of the opposite geometric isomer was a l s o demonstrated with males of the o r i e n t a l f r u i t moth, Grapholitha molesta (22). Females of t h i s species emit ( Z ) - 8 dodecenyl acetate as a major sex pheromone component, along w i t h a s y n e r g i s t , dodecyl alcohol (23). A d d i t i o n of the (E)-isomer o f 8-dodecenyl a c e t a t e increased male catches about 2 5 - f o l d ; maximum a t t r a c t i v e n e s s occurred w i t h about 8% of t h i s isomer. The o l f a c t o r y b a s i s f o r the great d i s c r i m i n a t o r y a b i l i t i e s of male moths v i s - a - v i s geometric isomers i s unknown, but i t s presence provides an elegant mechanism f o r developing a h i g h l y s p e c i f i c sex pheromonal blend. These pheromonal developments c l e a r l y demonstrate t h a t i n s e c t s are remarkable odor s p e c i a l i s t s , but i t would be inapprop r i a t e to l o s e t r a c k of the f a c t t h a t t h i s o l f a c t o r y prowess i s predicated on t h e i r a b i l i t y to b i o s y n t h e s i z e a p l e t h o r a of v o l a t i l e chemical s t i m u l i . I t seems appropriate a t t h i s j u n c t u r e

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to examine i n s e c t s as the v e r s a t i l e natural product chemists t h a t have reduced communication to a pheromonal a r t .

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Chemistry of Insect

Pheromones

Although pheromones are probably ubiquitous among species i n the I n s e c t a , s e r i o u s chemical i n v e s t i g a t i o n s of these compounds have been l i m i t e d to species i n about only one-fourth of the o r ders. Pest s p e c i e s , p a r t i c u l a r l y those i n the orders Lepidoptera and C o l e o p t e r a , have been subjected to c o n s i d e r a b l e pheromonal s c r u t i n y , and our knowledge of the chemistry of sex pheromones i s p r i m a r i l y derived from compounds i s o l a t e d from moths and b e e t l e s . On the other hand, the ants and bees (Hymenoptera) have proven to be an e s p e c i a l l y r i c h source of chemical r e l e a s e r s of s o c i a l behavior, and c h e m i s o c i a l i t y i s now being explored more and more f r e q u e n t l y i n terms of i d e n t i f i e d s i g n a l molecules. The a v a i l a b i l i t y of pure pheromones has made i t p o s s i b l e to analyze some aspects of i n s e c t behavior w i t h f a r greater i n c i s i v e ness than was ever p r e v i o u s l y p o s s i b l e ( 2 4 ) . The f r u i t s of the interphase between chemistry and animal behavior may be soon a v a i l a b l e f o r a g r i c u l t u r a l use ( 2 ) . Dictyoptera. Notwithstanding the economic importance of t e r m i t e s and cockroaches, r e l a t i v e l y few pheromones have been i d e n t i f i e d i n species i n t h i s order. In the case of t e r m i t e s , most of the chemical research has been undertaken on t r a i l pheromones, which are u t i l i z e d f o r a v a r i e t y of c r i t i c a l s o c i a l f u n c t i o n s , such as emigration and recruitment to nest breaks or food f i n d s . Matsumura e t a K (25) i d e n t i f i e d (ZvZ,E_)-3,6,8-dodecatrien-lo l i n e x t r a c t s of the t e r m i t e R e t i c u l i t e r m e s f l a v i p e s and reported that t h i s compound was a powerful r e l e a s e r of t r a i l f o l l o w i n g f o r workers. However, t h i s compound i s a l s o produced by the fungus L e n z i t e s trabea which i n f e c t s the wood fed upon by R. f l a v i p e s . The s i g n i f i c a n c e of the dodecatrienol i n the biology of t h i s t e r m i t e has r e c e n t l y been examined i n considerable d e t a i l (26). A diterpene hydrocarbon, assigned the t r i v i a l e p i t h e t nasutene, has been reported to be the t r a i l pheromone of Nasutitermes e x i t i o s u s ( 2 7 ) . This compound, which contains an unusual 14-membered r i n g s t r u c t u r e , has been assigned the s t r u c ture of neocembrene-A ( I ) . Neocembrene can be derived from C--^C c y c l i z a t i o n of geranylgeranyl pyrophosphate. 1 4

I

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Although t h i s compound has not y e t been i d e n t i f i e d i n the Eucalyptus wood fed upon by NL e x i t i o s u s , i t has been i s o l a t e d from Indian incense cedar Commiphora mokul ( 2 8 ) . Thus, as i n the case of R. f l a v i p e s , the compound reported to be the t r a i l pheromone of H. e x i t i o s u s may represent a p l a n t natural product. Cephalic alarm pheromones are secreted by s o l d i e r s of t e r mites i n the genera Drepanotermes and Ami termes ( 2 9 ) . These compounds have been i d e n t i f i e d as limonene and t e r p i n o l e n e , two of several monoterpene hydrocarbons forming p a r t of the defensive b a t t e r y of these i n s e c t s . Among the cockroaches, two chemical r e l e a s e r s of sexual behavior have been r e c e n t l y c h a r a c t e r i z e d . Females of B l a t t e ! l a germanica produce two sex pheromones, both of which appear to be a c t i v e by contact chemoreception. One of these compounds, 3 , 1 1 dimethyl-2-nonacosanone, produces wing r a i s i n g i n the male and i s perceived through antennal chemoreceptors (30). The absolute c o n f i g u r a t i o n of t h i s d i a s t e r e o m e r i c ketone has not been determined. A t e n t a t i v e s t r u c t u r e has been presented f o r one of the two sex pheromones emitted by females of the American cockroach, P e r i p l a n e t a americana. This compound, p r e v i o u s l y assigned the t r i v i a l name periplanone-B ( 3 1 ) , contains a ten-membered a l i c y c l i c r i n g and a germacrane-type s k e l e t o n (32). Based on d e t a i l e d NMR analyses and b i o g e n e t i c c o n s i d e r a t i o n s , a germacrene d e r i v a t i v e c o n t a i n i n g a non-conjugated ketone and two epoxide groups i s postulated ( I I ) . S i g n i f i c a n t l y , germacrene-D has been p r e v i o u s l y demonstrated to possess c o n s i d e r a b l e a c t i v i t y as a sex pheromone f o r males of F\ americana (33). Proof of

II s t r u c t u r e , based on unambiguous s y n t h e s i s , w i l l be awaited w i t h great i n t e r e s t by the s c i e n t i f i c community, e s p e c i a l l y s i n c e t h i s compound has c o n s t i t u t e d a real w i l l - o f - t h e - w i s p among i n s e c t sex pheromones. Orthoptera. The phase transformation of the l o c u s t Locusta m i g r a t o r i a from a s o l i t a r y to a gregarious (migratory) form i s pheromonally t r i g g e r e d during aggregations of these i n s e c t s . One of the compounds r e s p o n s i b l e f o r inducing morphom e t r i c , m e l a n i c , and behavioral changes i s 2-methoxy-5e t h y l p h e n o l , a guaiacol d e r i v a t i v e which has been termed l o c u s t o l (34). This compound may be produced i n the crops of grasshopper larvae from 1 i g n i n - d e r i v e d guaiacol and subsequently excreted i n

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the f e c e s . Whether l o c u s t o l i s synthesized de novo by the i n s e c t or produced by the m i c r o b i a l f l o r a of the crop has not been determined. Homoptera. Many species of a p h i d s , whose aggregations are e s p e c i a l l y s u s c e p t i b l e to p r é d a t i o n by a m u l t i t u d e of p r e d a t o r s , s e c r e t e alarm ( d i s p e r s i v e ) pheromones from the c o r n i c l e s when a t t a c k e d . This pheromone, which i s a minor c o n s t i t u e n t i n the c o r n i c u l a r s e c r e t i o n , has been i d e n t i f i e d as ( Ε ) - β - f a r n e s e n e i n a wide range of aphid species (35, 3 6 ) . Alarm behavior, which r e s u l t s i n aphids d i s p e r s i n g from the emission source e i t h e r by walking or f a l l i n g from the l e a f , i s h i g h l y adaptive s i n c e i t reduces the p r o b a b i l i t y t h a t a predator w i l l encounter other aphids a f t e r the i n i t i a l a t t a c k . However, ant-attended aphids show l e s s of a d i s p e r s i v e propensity than non-myrmecophilous s p e c i e s , i n d i c a t i n g that the presence of ants increases the t h r e s h ­ o l d f o r d i s p e r s i o n of aphid species ( 3 7 ) . I n t e r e s t i n g l y , ants r e ­ spond a g g r e s s i v e l y to ( E j - β - f a r n e s e n e , thus p r o v i d i n g one of the few examples of a pheromone being h i g h l y adaptive to both the e m i t t e r and r e c e i v e r i n d i v i d u a l s . R e c e n t l y , germacrene-A ( I I I ) has been i d e n t i f i e d as the alarm pheromone of the sweet c l o v e r aphid Therioaphis t r i f o l i i (38). This alarm r e l e a s e r , which has often been proposed as the progenitor of c y c l i c sesquiterpenes, c o n s t i t u t e s the second compound with a germacrane-type skeleton to be i d e n t i f i e d as an i n s e c t pheromone.

III Hemiptera. As i n the case of a p h i d s , hemipterous larvae often form dense aggregations which can serve as a r e a l bonanza f o r voracious predators. However, when t a c t u a l l y s t i m u l a t e d , l a r v a l hemipterans such as Dysdercus intermedius l i b e r a t e the contents of t h e i r dorsal abdominal g l a n d s , a response that r e ­ s u l t s i n the bugs d i s p e r s i n g (39). This alarm pheromone has been i d e n t i f i e d as (!E)-2-hexenal, a compound which i s u t i l i z e d de­ f e n s i v e l y by many species of true bugs. A d u l t s of the bedbug Cimex l e c t u l a r i u s a l s o respond d i s p e r s i v e l y to t h e i r main defensive compounds, (Ej-2-hexenal and ( E ) - 2 - o c t e n a l ( 4 0 ) . The simultaneous u t i l i z a t i o n of a defensive compound as an i n t r a s p e c i f i c chemical r e l e a s e r of behavior emphasizes the adaptiveness r e s u l t i n g from a s i n g l e exocrine compound subserving m u l t i p l e functions. In many hemipterous f a m i l i e s , l o n g - d i s t a n c e a t t r a c t i o n of

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the sexes r e s u l t s from the emission of sex pheromones by the males. In the c o r e i d Leptoglossus phyllopus the sex pheromones have been i d e n t i f i e d as a s e r i e s of aromatic compounds t h a t are released from a p a i r of abdominal glands opening through the 7-8th abdominal intersegmental membrane (41). The main con­ s t i t u e n t s present i n the s e c r e t i o n are benzyl a l c o h o l ( I V ) , guaiacol ( V ) , and syringaldehyde ( V I ) . In a d d i t i o n , v a n i l l i n ( V I I ) , methyl £ - h y d r o x y b e n z o a t e ( V I I I ) , and acetosyringone (IX)

HyO

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OH

OH IV

VI

ΟγΟ

ou- 0τ OH

VII

VOH III

ν

OH IX

occur as concomitants. Since males of 1^. phyllopus i n i t i a l l y c o l o n i z e new h a b i t a t s , t h i s a r o m a t i c - r i c h s e c r e t i o n i s probably u t i l i z e d as a long-range a t t r a c t a n t i n order to draw females to newly-invaded areas. D i p t e r a . C u t i c u l a r hydrocarbons derived from females have been reported to f u n c t i o n as short range sex a t t r a c t a n t s f o r a l l the species of f l i e s t h a t have been examined. ( Z j - 9 - T r i c o s e n e was i d e n t i f i e d as the sex pheromone of the house f l y , Musca domestica, whereas C27 and C29 c u t i c u l a r monoolefins were only weakly a c t i v e (42). Furthermore, ( Z ) - 9 - t r i c o s e n e was reported to f u n c t i o n as a sexual e x c i t a n t as w e l l , s i n c e the incidence of copulatory attempts by male f l i e s was reported to be increased i n the presence of t h i s compound. I t was subsequently suggested t h a t (Zj-9-heneicosene was an o r i e n t a t i o n pheromone f o r male f l i e s , and a 7:3 r a t i o of the C23 and C21 alkenes was optimal i n terms of o r i e n t a t i o n and mating behavior (43). However, n e i t h e r hydrocarbon increased the a t t r a c t i o n of male f l i e s to moving dummies ( 4 4 ) , and i t was e v e n t u a l l y concluded t h a t these l o n g chain ( Z J - 9 - a l k e n e s functioned p r i m a r i l y as psychedelics w i t h regard to v i s u a l l y s t i m u l a t e d sex a t t r a c t i o n and aggregation (45). A l a r g e s e r i e s of ( Z j - 9 - a l k e n e s enhanced the r e l e a s i n g e f f e c t i n conjunction w i t h the o p t i c a l s t i m u l i of sex a t t r a c t i o n r e s u l t i n g from the presence of dummy f l i e s . By themselves, the monoolefins showed l i t t l e promise f o r the c o n t r o l of h o u s e f l i e s (45). Several monoolefins were reported to f u n c t i o n as short-range sex a t t r a c t a n t s f o r male face f l i e s , Musca autumnal i s (46). In order of decreasing a c t i v i t y , (Zj-14-nonacosene, (ZJ-13-nonacosene, and (Z)-13-heptacosene were demonstrated to i n c r e a s e the i n c i ­ dence of male s t r i k e s a t females. These c u t i c u l a r c o n s t i t u e n t s were present i n both sexes, as were nonacosane and heptacosane, two alkanes reported to attenuate the a c t i v i t y of the monoolefins.

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However, s i n c e males contain a much higher proportion of saturated and unsaturated hydrocarbons than females, i t has been suggested t h a t sexual d i s c r i m i n a t i o n may be based on the proportions of the alkanes and alkenes ( 4 6 ) . A l a r g e s e r i e s of c u t i c u l a r hydrocarbons extracted from the female s t a b l e f l y , Stomoxys c a l c i t r a n s , i s reported to f u n c t i o n as a sex pheromone (47). ( Z ) - 9 - H e n t r i a c o n t e n e , ( Z j - 9 t r i t r i a c o n t e n e , and methyl-branched h e n t r i a - and t r i t r i a c o n t e n e s possessed a c t i v i t y as sexual r e l e a s e r s . In a d d i t i o n , mono- and d i m e t h y l - s u b s t i t u t e d h e n t r i a - and t r i t r i a c o n t a n e s were a l s o demonstrated to induce m a t i n g - s t r i k e behavior i n male f l i e s . However, these compounds may a c t u a l l y f u n c t i o n as p s y c h e d e l i c s , as does ( Z j - 9 - t r i c o s e n e f o r the housefly (45). Coleoptera. At t h i s j u n c t u r e , beetles appear to be the most v e r s a t i l e sex a t t r a c t a n t chemists i n the I n s e c t a . The s t r u c t u r e s of sex a t t r a c t a n t s from coleopterous species i n s i x f a m i l i e s have been determined, and there are scant grounds f o r g e n e r a l i z i n g about the exocrine chemistry of the species i n t h i s l a r g e order. Lacking any thread of chemical c o n t i n u i t y among beetles i n d i f f e r e n t t a x a , i t seems appropriate to examine t h e i r natural product i d i o s y n c r a c i e s as a f a m i l y q u a l i t y . 1. E l a t e r i d a e . Females of the sugar beet wireworm, Limonius c a l i f o r n i c u s , u t i l i z e n-pentanoic a c i d ( v a l e r i c ) as a l o n g - d i s t a n c e sex pheromone ( 4 8 j . Each female synthesizes i n excess of 100 p g . of t h i s a c i d , which i s presumably stored i n the sex a t t r a c t a n t gland i n an i n a c t i v e form. Isomeric C5 a c i d s possess no demonstrable a c t i v i t y as sex pheromones. 2. Bruchidae. Males of the d r i e d bean b e e t l e , Acanthoscelides o b t e c t u s , produce (-)-methyl ( E j - 2 , 4 , 5 t e t r a d e c a t r i e n o a t e , the only a l l e n i c sex pheromone i d e n t i f i e d i n i n s e c t s ( 4 θ ) . Each b e e t l e produces 10-20 Mg. of t h i s compound, which may be accompanied by a c l o s e l y - r e l a t e d e s t e r , p o s s i b l y methyl ( E _ ) - 2 , 4 , 6 - t e t r a d e c a t r i e n o a t e . The r o l e of t h i s compound as a sex pheromone has not been unambiguously e s t a b l i s h e d . 3 . Scarabaeidae. Phenol i s reported to be the sex a t t r a c ­ t a n t f o r males of the grass grub b e e t l e , C o s t e l y t r a z e a l a n d i c a , a major economic pest of pastures i n New Zealand (50j~! I t was subsequently reported that phenol was synthesized i n the c o l l e t e r i a l g l a n d s , not by the female b e e t l e , but r a t h e r by the b a c t e r i a l f l o r a which was housed t h e r e i n (51). However, i t has not been e s t a b l i s h e d whether or not phenol i s a l s o synthesized de novo by the female scarab. I f t h i s were the c a s e , the presence of the b a c t e r i a i n the c o l l e t e r i a l glands would simply demonstrate the a b i l i t y of these microorganisms to r e s i s t the b a c t e r i o c i d a l p r o p e r t i e s of phenol, a c h a r a c t e r i s t i c common to many species i n

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the Enterobacteriaceae. Females of the Japanese b e e t l e , P o p i l l a j a p o n i c a , synthesize one of the few l a c t o n i c sex pheromones t h a t have been i d e n t i f i e d i n i n s e c t s (52). Tumlinson et j f L (52) have r e c e n t l y i d e n t i f i e d the powerful sex pheromone of t h i s i n s e c t as ( R , Z ) - 5 ( l - d e c e n y l ) d i h y d r o - 2 ( 3 H ) - f u r a n o n e (X). In a d d i t i o n to the Zisomer, the Ε - i s o m e r i s a l s o present as w e l l as the saturated

homolog. The r a t i o of Ζ-, E-, and saturated isomers i n the female i s about 84/13/3, r e s p e c t i v e l y . I t was a l s o demonstrated that mixtures of eugenol and phenylethyl propionate, which con­ s t i t u t e a good a t t r a c t a n t f o r both male and female beetles ( 5 3 ) , synergized the a t t r a c t i v e n e s s of the pheromone f o r both sexes. The a v a i l a b i l i t y of t h i s potent sex pheromone should now make i t p o s s i b l e to both monitor b e e t l e i n f e s t a t i o n s and c o n t r o l these i n s e c t s through the use of a r a t i o n a l trapping program. 4. C u r c u l i o n i d a e . The b o l l w e e v i l , Anthonomus g r a n d i s , that great d e s p o i l e r of cotton i n the southern U. S . , synthesizes a quaternary blend of sex pheromones t h a t have been c o l l e c t i v e l y l a b e l e d grandlure. Four compounds t h a t i n t e r a c t s y n e r g i s t i c a l l y have been i d e n t i f i e d as ( + ) - 2 - ( c i s - i s o p r o p e n y l - 1 - m e t h y l c y c l o b u t y l ) ethanol ( X I ) , ( Z ) - 2 - ( 3 , 3 - d i m e t h y l c y c l o h e x y l i d e n e ) e t h a n o l ( X I I ) , U)-2-(3,3-dimethylecyclohexylidene)acetaldehyde ( X I I I ) , and (E)-2-(3,3-dimethylcycloh.exylidene)acetaldehyde (XIV) ( 5 4 ) . Traps b a i t e d w i t h a mixture of these male-derived terpenoids a t t r a c t females from d i s t a n c e s of at l e a s t ten meters.

XII

XIII

XIV

5. Dermestidae. The sex pheromones of the so c a l l e d carpet beetles appear to be g e n e r a l l y i d e n t i f i e d w i t h unsaturated normal or monomethyl-substituted a l c o h o l s , a c i d s , or e s t e r s . Females of the black carpet b e e t l e , Attagenus megatoma, u t i l i z e

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(IE,Z_)-3,5-tetradecadienoic a c i d as a sex a t t r a c t a n t (55). The sexual r e l e a s e r emitted by females of the f u r n i t u r e carpet b e e t l e , Anthrenus f l a y i p e s , has been i d e n t i f i e d as ( Z j - 3 - d e c e n o i c a c i d (56). The U)-isomer i s about 20X more a c t i v e than the ( E ) isomer. Two of the sexual r e l e a s e r s secreted by females of Trogoderma inclusum have been i d e n t i f i e d as ( Z ) - ( - ) - 1 4 - m e t h y l 8 - h e x a d e c e n - l - o l and (-)-methyl (Z)-14-methyl-8-hexadecenoate (57). Each of these compounds i s a c t i v e by i t s e l f and i n a d d i t i o n , two u n i d e n t i f i e d pheromones are present i n the sex a t t r a c t a n t blend. The alcohol i s a t t r a c t i v e to f i v e other species of Trogoderma, making i t seem l i k e l y t h a t s i m i l a r compounds are u t i l i z e d as sex pheromones by many species i n t h i s genus. Indeed, Yarger et al_. (58) i d e n t i f i e d methyl ( £ ) - 1 4 - m e t h y l - 8 - h e x a d e c e n o a t e and ( Ë J - 1 4 m e t h y l - 8 - h e x a d e c e n - l - o l i n e x t r a c t s of females of T. glabrum. In a d d i t i o n , ι ι - h e x a n o i c a c i d , methyl (Zj-7-hexadecenoate and 4-hydroxyhexanoic a c i d l a c t o n e (/-caprolactone) (XV) have been i d e n t i f i e d as part of the sex a t t r a c t a n t blend. A l l of these compounds are i n d i v i d u a l l y a c t i v e .

XV

6. S c o l y t i d a e . The worldwide ranges of bark beetles have made them i d e a l candidates f o r research d i r e c t e d toward the i s o ­ l a t i o n and i d e n t i f i c a t i o n of pheromones t h a t can be used f o r population monitoring and r e g u l a t i o n . A decade ago, the aggre­ g a t i v e pheromone l i b e r a t e d by males of Ips paraconfusus (=confusus) was i d e n t i f i e d as a mixture of ( - ) - 2 - m e t h y l - 6 methylene-7-octen-4-ol ( i p s e n o l ) (XVI), ( + ) - c i s - v e r b e n o l ( X V I I ) , and ( + ) - 2 - m e t h y l - 6 - m e t h y l e n e - 2 , 7 - o c t a d i e n - 4 - o l ( i p s d i e n o l ) ( X V I I I ) .

Maximum a t t r a c t i o n of beetles required the presence of a l l three compounds, although p a i r s of compounds were weakly a c t i v e (12). Other Ips species employ these pheromones i n combination w i t h host v o l a t i l e s as aggregative chemical t o c s i n s (59, 6 0 ) .

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The f r a s s o f females of the western pine b e e t l e Dendroctonus brevicomis i s enriched with endo- (XIX) and e x o - 7 - e t h y l - 5 - m e t h y l 6 , 8 - d i o x a b i c y c l o t 3 . 2 . 1 ] o c t a n e (XX), which are assigned the t r i v i a l e p i t h e t s endo- and exo-brevicomin ( 6 1 ) . Males of £ . brevicomis synthesize 1 , 5 - d i m e t h y l - 6 , 8 - d i o x a b i c y c l ο [ 3 . 2 . 1 ] o c t a n e ( f r o n t a l i n ) (XXI) i n t h e i r hind guts ( 6 2 ) , and t h i s compound, i n combination with the brevicomins and h o s t - d e r i v e d myrcene, c o n s t i t u t e s a potent a t t r a c t a n t f o r both sexes of D>. brevicomis ( 6 3 ) . Fron­ t a l i n , a l s o produced by females of Ό. f r o n t a l i s (62J7 i s reported to f u n c t i o n as a powerful aggregative pheromone when combined w i t h host monoterpenes such as a - p i n e n e ( 6 4 ) . D.. pseudotsugae

XXI i s a l s o reported to produce f r o n t a l i n (65) i n combination with 3 - m e t h y l - 2 - c y c l o h e x e n - l - o n e (66) and 3 - m e t h y l - 2 - c y c l o h e x e n - l - o l (67). A potpourri of f u n c t i o n s have been assigned to these Dendroctonus exocrine products, and the reader i s r e f e r r e d to the e x c e l l e n t review by Borden (68) f o r an a n a l y s i s of these f i n d i n g s . A population aggregation pheromone has been i d e n t i f i e d from males of the s c o l y t i d , Gnathotrichus s u l c a t u s ( 6 9 ) . A 65/35 mix­ ture of the (S)-(+) and the ( R ) - ( - ) enantiomers of 6-methyl-5hepten-2-ol ( s u l c a t o l ) was i s o l a t e d from the boring dust and shown to a t t r a c t both females and males i n a r a t i o of 2 . 6 5 : 1 , respectively. The t e r p e n o i d - e x o c r i n e theme emphasized by s c o l y t i d b e e t l e s was again evident when the chemical c o n s t i t u t i o n of the secondary a t t r a c t a n t f o r the s m a l l e r European elm bark b e e t l e , Scolytus m u l t i s t r i a t u s , was e l u c i d a t e d . The aggregation pheromone was i d e n t i f i e d as a mixture of ( - ) - 4 - m e t h y l - 3 - h e p t a n o l , 2 , 4 - d i m e t h y l 5-ethyl-6,8-dioxabicyclo [3.2.1]octane ( m u l t i s t r i a t i n ) (XXII), and (-)-a-cubebene ( X X I I I ) , a h o s t - d e r i v e d s y n e r g i s t ( 7 0 ) . A l l three compounds are required f o r the maximum a t t r a c t i o n of b e e t l e s . The i n a c t i v e diastereomers of 4-methyl-3-heptanol and m u l t i s t r i a t i n d i d not i n h i b i t the responses of a i r b o r n e b e e t l e s .

XXII

XXIII

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Lepidoptera. Lepidopterous sex pheromones, p a r t i c u l a r l y those produced by female moths, have been p r i m a r i l y determined to be unsaturated normal a l i p h a t i c a l c o h o l s , e s t e r s , or aldehydes (3_ 10, 7 1 ) . In the present review, emphasis w i l l be placed on the sex pheromones t h a t e i t h e r are s t r u c t u r a l l y d i s t i n c t i v e or r e p r e s e n t a t i v e of the general c l a s s e s of compounds t h a t are i d e n t i f i e d w i t h l e p i dopterous s p e c i e s . Notwithstanding the t e r m i n o l o g i c a l i n e x a c t i tude t h a t c h a r a c t e r i z e s the research on lepidopterous exocrine products ( 7 2 ) , these compounds w i l l be r e f e r r e d to as sex a t t r a c t a n t s or pheromones unless otherwise i n d i c a t e d . The sex a t t r a c t a n t of the eastern spruce budworm, Choristoneura f u m i f e r a n a , i s ( E ) - l l - t e t r a d e c e n a l ( 7 3 ) . A probable p r e c u r s o r , ( E ) - l l - t e t r a d e c e n - l - o l , i s produced i n the sex a t t r a c t a n t gland ( 7 4 ) , but t h i s compound, which i n h i b i t s the male response to the aldehyde, does not appear to be released by the c a l l i n g female. The (Z)-isomer of tetradecenal has been i d e n t i f i e d as one of the sex pheromones of the tobacco budworm, H e l i o t h i s v i r e s c e n s ; i t i s accompanied by (Z_)-ll-hexadecenal (75, 76)." S i m i l a r l y , the female of the s t r i p e d r i c e borer secretes two a l k e n a l s - - ( Z j - l l - h e x a d e c e n a l and ( Z ) - 1 3 - o c t a d e c e n a l - as i t s sex pheromone blend (77). Females of the l y m a n t r i i d , P o r t h e t r i a d i s p a r , the gypsy moth, l i b e r a t e cis-7,8-epoxy-2-methy1octadecane ( d i s p a r l u r e ) as a sex pheromone (78). The probable precursor of the epoxide, ( Z j 2-methyl-7-octadecene, i s present i n the gland i n l a r g e quant i t i e s , and i t has been demonstrated t h a t the o l e f i n i s epoxidized i n v i v o (79). D i s p a r l u r e i s r a p i d l y adsorbed on the male antennae and q u i c k l y converted to two more p o l a r m e t a b o l i t e s ( 8 0 ) , probably as a consequence of h y d r o l y s i s of the epoxide group. A r c t i i d s i n the Holomelina a u r a n t i a c a complex u t i l i z e 2 methylheptadecane as part of t h e i r sex pheromone complex ( 8 1 ) . This compound a t t r a c t e d males of a t l e a s t e i g h t species i n t h i s complex, but i n the case of a t l e a s t some of these s p e c i e s , the presence of a n c i l l a r y pheromones was i n d i c a t e d . Although homologous 2-methylalkanes were i n a c t i v e as a t t r a c t a n t s , 2 , 1 5 dimethylheptadecane was about one tenth as a c t i v e as 2-methylheptadecane. The sex pheromone of the Douglas f i r tussock moth, O r g y i a pseudotsugata, c o n s t i t u t e s the only ketonic sex pheromone t h a t has been i d e n t i f i e d i n a species of moth. This compound, ( 7 ) - 6 - h e n e i c o s e n - l l - o n e , i s a powerful a t t r a c t a n t f o r males both under l a b o r a t o r y and f i e l d c o n d i t i o n s , as i s the ( £ ) - i s o m e r ( 8 2 ) . Although acetate e s t e r s are commonly encountered as lepidopterous sex pheromones, the occurrence of other e s t e r s has proven to be a very unusual phenomenon. This f a c t renders the sex pheromone of the pine emperor moth, Nudaurelia c y t h e r e a , h i g h l y d i s t i n c t i v e , s i n c e t h i s compound, (Z_)-5-decenyl 3 methylbutyrate ( 8 3 ) , represents an e s t e r c o n t a i n i n g a C5 a c i d . That other s a t u r n i i d moths produce unusual sex pheromones i s 9

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demonstrated by the report t h a t females of another s i l k m o t h , Antheraea polyphemus, secrete a sex pheromone c o n s i s t i n g of a 9 : 1 mixture o f (E,Z)-6TÏÎ-hexadecadienyl acetate and ( £ , Z _ ) - 6 , 1 1 hexadecadienal ( 8 4 ) . This i s the only example of a sex a t t r a c t a n t composed o f both an aldehyde and e s t e r . I t now seems evident that the s p e c i f i c i t y of sex pheromones i s predicated on the u t i l i z a t i o n of r e l a t i v e l y exact blends of compounds. For example, Hummel et al^. (85) i d e n t i f i e d U,Z)-7,11hexadecadienyl acetate and U,Ej-7,ll-hexadecadienyl acetate as the sex pheromones of the pink bollworm, Pectinophora g o s s y p i e l l a . The pheromonal m i x t u r e , gossyplure, was h i g h l y a c t i v e when e v a l u ated i n the f i e l d , and f i n a l l y provided a r e l i a b l e tool f o r c h a l l e n g i n g t h i s p e r n i c i o u s pest of c o t t o n . S i m i l a r l y , Tamaki e t a l . Ç86) reported t h a t the sex pheromone of Adoxophyes f a s c i a t a was composed of two geometric isomers, ( Z j - 9 - t e t r a d e c e n y l acetate and CZ.)-ll-tetradecenyl a c e t a t e . The c l o s e l y r e l a t e d summer f r u i t t o r t r i x , Adoxophyes orana, a l s o u t i l i z e d the same compounds as sex pheromones, but q u a n t i t a t i v e d i f f e r e n c e s i n the male response to the d i f f e r e n t proportions of these acetates produced by these two species appears to maintain species i s o l a t i o n (87_). Sens i t i v i t y o f males to d i f f e r e n t r a t i o s of these two compounds i s a l s o reported to be r e s p o n s i b l e f o r the sexual i s o l a t i o n of A. orana from C l e p s i s spectrana (88). T e r t i a r y pheromonal blends have been i d e n t i f i e d i n two noctuid moths. The red bollworm, Diparopsis castanea, emits dodecyl a c e t a t e , (Ej-9-dodecenyl a c e t a t e , 11-dodecenyl a c e t a t e , and (E)-9,ll-dodecadienyl acetate as a sex pheromone, whereas Spodoptera l i t t o r a l i s u t i l i z e s a blend made up o f t e t r a d e c y l a c e t a t e , (.EJ-9-tetradecenyl a c e t a t e , (Ej-ll-tetradecenyl a c e t a t e , and ( Ζ , Ε ) - 9 , 1 1 - t e t r a d e c a d i e n y 1 acetate ( 8 9 ) . For both s p e c i e s , the conjugated dienes are the most potent o l f a c t o r y s t i m u l a n t s . On the other hand, the sex pheromones of both S^. l i t t o r a l i s and S^. l i t u r a were reported to c o n s i s t of binary mixtures of (Z_,£)9 , 1 1 - t e t r a d e c a d i e n y l acetate and ( Ζ , Ε ) - 9 , 1 2 - t e t r a d e c a d i e n y 1 acetate (90, 9 1 ) . The presence of a d d i t i o n a l compounds i n the sex phero­ mone blend i s believed to be r e s p o n s i b l e f o r the sexual i s o l a t i o n of these two Spodoptera species from each other. Both the Indian meal moth, P l o d i a i n t e r p u n c t e l l a , and the almond moth, Cadra c a u t e l l a , u t i 1 i ze (Z_,EJ - 9 , 1 2 - t e t r a d e c a d i enyl acetate as a primary sex pheromone (92, 9 3 ) . In a d d i t i o n , (Z.)-9tetradecen-l-ol has been i d e n t i f i e d as part of the sex pheromone °f c a u t e l l a (94). S i g n i f i c a n t l y , a t t r a c t i o n of almond moth males to t h e i r females i s s t r o n g l y i n h i b i t e d i n the presence of Indian meal moth females (95.). These r e s u l t s emphasize the probable presence of secondary components i n the sex pheromone blend that may play key r o l e s i n jamming the o l f a c t o r y responses of c l o s e l y - r e l a t e d and sympatrie s p e c i e s . On the other hand, Tumlinson e t al_. (96) demonstrated that two sympatric species of moths were r e p r o d u c t i v e l y i s o l a t e d , based on the u t i l i z a t i o n of d i f f e r e n t geometric isomers of the

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same compound to which the males e x h i b i t e d s e l e c t i v e o l f a c t o r y responses. The female of the l e s s e r peachtree b o r e r , Synanthedon p i c t i p e s , secretes ( £ , Z j - 3 , 1 3 - o c t a d e c a d i e n y l a c e t a t e , whereas the peachtree borer, Sanninoidae e x i t i o s a , u t i l i z e s the (Ζ,,Ζ.)-isomer as a sex pheromone. Furthermore, whereas low concentrations of the (E,ZJ-isomer d i d not i n t e r f e r e with the response of males of S_. e x i t i o s a , the presence of low concentrations of the isomer i n h i b i t e d the response of p i c t i p e s males to t h e i r own sex pheromone. An i n t e r e s t i n g case of geographical v a r i a t i o n i n sex a t t r a c t a n t s e n s i t i v i t y was i l l u m i n a t e d by Roelofs e t al_. ( 9 7 ) . Females of the f r u i t t r e e r o l l e r , Archips a r g y r o s p i l u s , secrete a sex pheromone c o n t a i n i n g dodecyl a c e t a t e , ( E j - and (Z_)-11tetradecen-l-ol, and ( E ) - and (Zj-ll-tetradecenyl a c e t a t e . However, males from a population i n B r i t i s h Columbia responded to a wide range of (E.)- and (Zj-ll-tetradecenyl acetate r a t i o s with dodecyl acetate a c t i n g as a s y n e r g i s t , whereas a New York population required a much more p r e c i s e r a t i o of isomeric acetates i n conjunction with the acetate s y n e r g i s t . Presumably, the New York population of A. a r g y r o s p i l u s has been under greater s e l e c ­ t i v e pressure to develop a more p r e c i s e d i s c r i m i n a t o r y system f o r the CE)- and U)-isomers than the B r i t i s h Columbia p o p u l a t i o n . Male moths and b u t t e r f l i e s have proven to be an e s p e c i a l l y r i c h source of i n t e r e s t i n g natural products. The sex pheromone produced i n the wing glands of the l e s s e r waxmoth, Achroia g r i s e l l a , i s composed of n-undecanal and ( Z j - l l - o c t a d e c e n a l ( 9 8 ) , whereas t h a t of the greater waxmoth a l s o contains n-undecanal (99) but i s dominated by ii-nonanal (100). The scent brushes of male noctuid moths produce l a r g e amounts of aromatic compounds and terpenes which are b e l i e v e d to f u n c t i o n as a p h r o d i s i a c s (101). Benzaldehyde, 2-phenylethanol, benzyl a l c o h o l , 6-methyl-5-hepten2-one, pinocarvone, and i s o b u t y r i c a c i d have been i d e n t i f i e d i n the s e c r e t i o n s of d i f f e r e n t noctuid species (102), and i t appears t h a t these pheromones may possess some chemotaxonomic value. S t r u c t u r a l i n v e s t i g a t i o n s on the sex pheromones of male b u t t e r f l i e s have y i e l d e d several unique i n s e c t exocrine products. The major components i n the h a i r p e n c i l s of the danaid Lycorea ceres ceres are c e t y l a c e t a t e , (Z)-vaccenyl a c e t a t e , and 2 , 3 d i h y d r o - 7 - m e t h y l p y r r o l i z i n - l - o n e (XXIV) (103). The dihydrop y r r o l i z i n o n e , as w e l l as ( £ , E j - 3 , 7 - d i m e t h y l d e c a - 2 , 6 - d i e n - l , 1 0 d i o l , have been i d e n t i f i e d from the h a i r p e n c i l s of the queen b u t t e r f l y , Danaus g i l i p p u s (104), and the former compound pos­ sesses pheromonal a c t i v i t y when evaluated e l e c t r o p h y s i o l o g i c a l ^ (105) and b e h a v i o r a l l y (106). The h a i r p e n c i l s of the monarch b u t t e r f l y , Danaus p l e x i p p u s , have y i e l d e d (E^E)-10-hydroxy-3,7(107) (E,E)-3,7-dimethyl-2,6decadien-l,10-dioic a c i d (108). On the other hand, the Old World monarch, Danaus chrysippus, contains (E_)-3,7-dimethyloct-2-en-l,8d i o l as w e l l as the p y r r o l i z i n o n e (XXIV) (109). Recently, Edgar e t a}_. (110) i d e n t i f i e d two new d i h y d r o p y r r o l i z i n e s i n the

dm i ethy-l2,6-deca de inoc i acd i

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h a i r p e n c i l s of danaid b u t t e r f l i e s . Several species of Danaus and Euploea y i e l d e d e i t h e r l - f o r m y l - 7 - h y d r o x y - 6 , 7 - d i h y d r o - 5 H p y r r o l i z i n e (XXV) alone or i n combination with the d i h y d r o p y r r i l i zinone (XXIV). The h a i r p e n c i l s of one s p e c i e s , Danaus a f f i n i s a l b i s t r i g a , contained i n a d d i t i o n to the d i h y d r o p y r r o l i z i n e (XXIV), l - f o r m y l - 6 , 7 - d i h y d r o - 5 H - p y r r o l i z i n e (XXVI). The d i v e r s i t y of a l k a l o i d s found i n danaid h a i r p e n c i l s was f u r t h e r emphasized by the i d e n t i f i c a t i o n of lycopsamine (XXVII) from Danaus hamatas hamatus and Euploea t o i l u s t o i l u s (111). The scent

brushes (coremata) of a r c t i i d moths i n the genus U t e t h e i s a a l s o c o n t a i n d i h y d r o p y r r o l i z i n e s (XXV) and (XXVI). L i k e the danaids, the males feed on plants c o n t a i n i n g p y r r o l i z i d i n e a l k a l o i d s and i t seems c e r t a i n t h a t the species i n both f a m i l i e s d e r i v e t h e i r d i h y d r o p y r r o l i z i n e s from t h e i r host p l a n t s (112). The scent s c a l e s on the wings of a male l y c a e n i d , Lycaeides argyrognomon, s e c r e t e a mixture of ιι-nonanal, hexadecyl a c e t a t e , and a sesquiterpene a l c o h o l , t e n t a t i v e l y i d e n t i f i e d as t o r r e y o l ( δ - c a d i n o l ) (XXVIII) (113); the absolute c o n f i g u r a t i o n of the sesquiterpene has not been determined. These male-derived pheromones appear to play an important r o l e i n the c o u r t s h i p behavior of t h i s s p e c i e s . Hymenoptera Chemical communication reaches i t s apogee i n the s o c i a l i n ­ s e c t s . Whereas the exocrine r e p e r t o i r e of gregarious or s o l i t a r y i n s e c t s i s e s s e n t i a l l y l i m i t e d to aggregative and/or sex phero­ mones, t h a t of the true s o c i a l i n s e c t s i s c h a r a c t e r i z e d by a d a z z l i n g v a r i e t y of s i g n a l compounds t h a t mediate a d i v e r s e con­ course of behavioral r e a c t i o n s ( 5 ) . The e v o l u t i o n of a m u l t i t u d e of exocrine glands (114) i n combination w i t h an e x t r a o r d i n a r y n a t u r a l product chemistry (115) have provided the a n t s , bees, and wasps w i t h the p o t e n t i a l f o r e x p l o i t i n g c h e m i s o c i a l i t y to i t s f u l l e s t . These hymenopterans have evolved a v a r i e t y of i d i o ­ s y n c r a t i c behavioral r e a c t i o n s which are now known to be t r i g g e r e d by pheromonal s t i m u l i , and i t seems probable t h a t most, i f not a l l , l e v e l s of i n s e c t s o c i a l i t y w i l l u l t i m a t e l y be determined to possess exocrine bases. Hymenopterous species can modulate the i n f o r m a t i o n a l content of the s i g n a l by simultaneously evacuating the contents of two g l a n d s , often r e s u l t i n g i n blends of s y n e r g i s t i c pheromones (116). In a d d i t i o n , there are cogent grounds f o r concluding t h a t the

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development of complex s o c i e t i e s i n the Hymenoptera r e s u l t e d , i n p a r t , from the c a p a c i t y of these i n s e c t s to evolve the a b i l i t y to e x h i b i t a v a r i e t y of behavioral responses to a s i n g l e chemical s t i m u l u s . Pheromonal parsimony (116), the a b i l i t y of an exocrine compound to subserve m u l t i p l e f u n c t i o n s , has made i t p o s s i b l e f o r hymenopterans to expand the dimensions of s o c i a l i t y f a r beyond what would have been p o s s i b l e w i t h a f i n i t e number of chemical r e l e a s e r s of behavior. In order to examine the chemisocial panorama as a f u n c t i o n of v o l a t i l e i n f o r m a t i o n - b e a r i n g agents, the wondrous world of the Hymenoptera w i l l be analyzed i n terms of s p e c i f i c behavioral r e a c t i o n s and t h e i r exocrine mediators. 1. Alarm Pheromones. Ants u t i l i z e a wide v a r i e t y of methyl and ethyl ketones to generate alarm s i g n a l s ( 5 ) . These compounds, which are present i n r e l a t i v e l y l a r g e q u a n t i t i e s , are produced by species i n most of the major s u b f a m i l i e s of a n t s . 2-Alkanones such as 2-heptanone, 6-methyl-5-hepten-2-one, and 4 - m e t h y l - 2 hexanone are p r i m a r i l y produced by d o l i c h o d e r i n e species (117, 118, 119) as products of the capacious anal glands. Myrmicines, on the other hand, p r i m a r i l y synthesize ethyl ketones, and seven of these compounds have been i d e n t i f i e d i n t h e i r s e c r e t i o n s . In a d d i t i o n to 3-octanone, 3-nonanone, and 3-decanone, the methylbranched ketones 4-methyl-3-hexanone, 4-methyl-3-heptanone, 6-methyl-3-octanone, and 4 , 6 - d i m e t h y l - 4 - o c t e n - 3 - o n e have been i d e n t i f i e d as r e l e a s e r s of alarm behavior (120, 121, 122). C i t r a l (123), formic a c i d (124), and n-undecane TÏ25) are among a host of other compounds i d e n t i f i e d as f o r m i c i d alarm pheromones. R e c e n t l y , Wheeler and Blum (126) reported that a l k y l pyrazines were secreted by Odontomachus spp. i n response to f o r e i g n s t i m u l i . Some species produced 2 , 5 - d i m e t h y l - 3 - i s o p e n t y l p y r a z i n e (XXIX) whereas 2 , 5 - d i m e t h y l - 3 - p e n t y l p y r a z i n e (XXX) and r e l a t e d compounds were produced by o t h e r s . Although these compounds are a t t r a c t a n t s that r e l e a s e a t t a c k behavior i n Odontomachus workers, ponerine species t h a t form small c o l o n i e s u t i l i z e one of the a l k y l p y r a z i n e s to r e l e a s e escape behavior (127).

XXIX

XXX

In a d d i t i o n to a c y c l i c ketones, d o l i c h o d e r i n e ants i n the genus Azteca generate an alarm s i g n a l w i t h 2-methylcyclopentanone ( x x x i ) , c i s - 1 - a c e t y l - 2 - m e t h y l c y c l o p e n t a n e (XXXII), and 2 - a c e t y l 3-methylcyclopentene (XXXIII) (128). That some ant species u t i l i z e aromatic compounds as alarm pheromones i s demonstrated by the i d e n t i f i c a t i o n of methyl 6 - m e t h y l s a l i c y l a t e (XXXIV) i n the

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ponerine Gnamptogenys pleurodon (129).

Ο

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XXXI

XXXII

XXXIII

XXXIV

Among bees, c i t r a l Ç130), 2-heptanone (131), and i s o p e n t y l acetate (132) have been shown to possess among other f u n c t i o n s , that of alarm r e l e a s e r s . 2. T r a i l Pheromones. Tumiinson et_ a l . (133) i d e n t i f i e d methyl 4 - m e t h y l p y r r o l e - 2 - c a r b o x y l a t e (XXXVT as the major t r a i l pheromone of the a n t , A t t a texana. Another poison gland product, 3 - b u t y l - 5 - m e t h y l o c t a h y d r o i n d o l i z i n e (XXXVI) has been reported to be the dominant r e l e a s e r of t r a i l f o l l o w i n g f o r workers of Monomorium pharaonis (134).In c o n t r a s t to these c y c l i c r e l e a s e r s

XXXV

xxxvi

of t r a i l f o l l o w i n g , Huwyler et al_. (135) demonstrated t h a t heptanoic, o c t a n o i c , nonanoic, decanoic, and dodecanoic acids were components of the t r a i l pheromone of Lasius f u l i g i n o s u s . S t i n g l e s s bees l a y chemical t r a i l s with mandibular gland c o n s t i t u e n t s which have been i d e n t i f i e d as normal a l i p h a t i c a l cohols or monoterpene aldehydes. Triqona s p i n i p e s generates a t r a i l w i t h a mixture of 2-heptanol, 2-undecanol, and 2 - t r i d e c a n o l , and i t has been p o s s i b l e to s u c c e s s f u l l y l a y a r t i f i c i a l t r a i l s w i t h these a l c o h o l s (136). T r a i l f o l l o w i n g i n workers of Triqona subterranea i s released by c i t r a l (130), the stereoisomers of which are a l s o u t i l i z e d as alarm pheromones and defensive compounds. Such pheromonal parsimony appears to be e s p e c i a l l y t y p i c a l of e u s o c i a l bees and a n t s . 3. Sex Pheromones. Gary (137) demonstrated t h a t (Ej-9-oxo2-decenoic a c i d , a mandibular gland product of the queen honey

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bee, Apis m e l l i f e r a , was a powerful a t t r a c t a n t f o r a i r b o r n e drones. This compound a l s o possesses a d d i t i o n a l f u n c t i o n s as a queen substance f o r workers i n the m i l i e u of the h i v e . Species of pine s a w f l i e s i n the genera Neodiprion and Pi prion secrete a sex pheromone dominated by e i t h e r the acetate or propionate e s t e r s of 3,7-dimethylpentadecan-2-ol (138). Reproductive i s o l a t i o n of these s a w f l i e s appears to be p a r t l y r e l a t e d to the u t i l i z a t i o n of one or the other of these diasteriomeric esters. 4. Queen Substance. The queens of many hymenopterous species r e l e a s e primer pheromones i n the c o l o n i a l m i l i e u and these compounds s t r o n g l y i n f l u e n c e the reproductive or endocrine systems of the workers. B u t l e r et a K (139) i d e n t i f i e d ( E j - 9 oxo-2-decenoic as the compound t h a t i n h i b i t s both ovarian development i n workers (140) and queen c e l l c o n s t r u c t i o n (141). The queen substance of the O r i e n t a l hornet has been i d e n t i f i e d as δ-hexadecalactone (XXXVII) (142).

XXXVII 5. Disarming Pheromones. C e r t a i n species of both bees and ants r a i d c o l o n i e s of other species of s o c i a l i n s e c t s i n order to a p p r o p r i a t e e i t h e r food or f o r e i g n workers which e v e n t u a l l y f u n c t i o n as s l a v e s . In the American t r o p i c s , the s t i n g l e s s bee L e s t r i m e l i t t a limao disarms c o l o n i e s of other s t i n g l e s s bees w i t h c i t r a l (143), the stereoisomers of which serve to e f f e c t i v e l y destroy the c o l o n i a l cohesion of the r a i d e d species (140). Citral a l s o f u n c t i o n s as an a t t r a c t a n t , alarm r e l e a s e r , and defensive substance f o r workers of U limao. Formicine ants e f f e c t i v e l y disarm workers of species whose nests they are r a i d i n g w i t h a l k y l a c e t a t e s , which o r i g i n a t e i n the w e l l developed Dufour's glands of the r a i d e r s (144). 6. T e r r i t o r i a l Pheromones. Males of many species of bumble­ bees mark s e l e c t e d s i t e s with l a b i a l gland products t h a t a t t r a c t both males and females. These t e r r i t o r i a l mating spots are "perfumed" with a wide v a r i e t y of a c y c l i c compounds t h a t appear to c o n s t i t u t e s p e c i e s - s p e c i f i c blends t h a t may promote r e p r o ­ d u c t i v e i s o l a t i o n among the species of Bombus and P s i t h y r u s (145). G e r a n y l g e r a n i o l , g e r a n y l c i t r o n e l l o l , geranylgeranyl a c e t a t e , 2 , 3 - d i h y d r o f a r n e s y l a c e t a t e , and ( E ) - f a r n e s y l a c e t a t e are among the d i s t i n c t i v e s e s q u i - and diterpenes u t i l i z e d by these bees to transform the branches of t r e e s i n t o p o t e n t i a l love n e s t s .

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Males of the carpenter bee, Xylocopa h i r u t i s s i m a , e s t a b l i s h and defend t e r r i t o r i e s t h a t are located proximate to p r o j e c t i n g t r e e s on mountain tops (146). These t e r r i t o r i e s are maintained by a mandibular gland s e c r e t i o n that c o n t a i n s , as a major c o n s t i t u e n t , the c i s - l a c t o n e of 2-methyl-5-hydroxyhexanoic a c i d (XXXVIII) (147).

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XXXVIII 7. F l i g h t I n i t i a t i o n Pheromones. The mating f l i g h t s of many species of carpenter ants are i n i t i a t e d by male mandibular gland s e c r e t i o n s (148). These chemical s t i m u l a t o r s of female f l i g h t appear to c o n s t i t u t e r e l a t i v e l y s p e c i e s - s p e c i f i c blends of compounds that are dominated by compounds such as 2 , 4 - d i m e t h y l 2-hexenoic a c i d , methyl 6-methyl s a l i c y l a t e (XXXIV), methyl a n t h r a n i l a t e (XXXIX), 10-methyldodecanoic a c i d , and the lactone m e l l e i n (XL) (149, 150). Recently, the s e x - s p e c i f i c blend of

XXXIX

XL

pheromones secreted by males of Camponotus c l a r i t h o r a x was c h a r a c t e r i z e d as a mixture of a l c o h o l s and e s t e r s , several of which c o n s t i t u t e unique arthropod natural products (151). In a d d i t i o n to 2 , 6 - d i m e t h y l - 5 - h e p t e n - l - o l and 2-phenylethanol, t h i s s e c r e t i o n contains the octanoate and the nonanoate e s t e r s of these a l c o h o l s , as well as c i t r o n e l l i c and geranic a c i d s . The s i g n i f i c a n c e of t h i s unusual Camponotus s e c r e t i o n has not been determined, although i t c e r t a i n l y must a c t as a reproductive i s o l a t i n g agent. 8. Chemical Releasers of Digging Behavior. The mandibular gland s e c r e t i o n s of several species of ants have been demonstrated to be r e l e a s e r s of digging behavior i n h i g h l y s t i m u l a t e d workers. Crewe and F l e t c h e r (152) reported that the a l k y l s u l f i d e s produced by the ant Paltothyreus t a r s a t u s - - d i m e t h y l d i s u l f i d e and dimethyl t r i s u l f i d e ( 1 5 3 ) - - 7 u n c t i o n to r e l e a s e h i g h l y o r i e n t e d digging behavior. This behavior i s h i g h l y adaptive s i n c e ant workers buried i n s o i l can s i g n a l t h e i r imprisonment to t h e i r s i s t e r workers and be subsequently excavated. Wilson (154)

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demonstrated t h a t the mandibular gland products of Pogonomyrmex badius released digging behavior i n workers, and Blum and Warter (155) reported t h a t 2-heptanone, the alarm pheromone of Conomyrma pyramicus, was a l s o capable of causing workers to excavate s o i l p a r t i c l e s .

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The C h i r a l World of Insects Many of the compounds t h a t c o n s t i t u t e chemical s i g n a l s i n the world of i n s e c t s c o n t a i n c h i r a l c e n t e r s , and i t now seems evident t h a t a v a r i e t y of i n s e c t s can d i s c r i m i n a t e these enantiomers with great o l f a c t o r y p r e c i s i o n . Insects are exposed to a m u l t i tude of enantiomeric p l a n t natural products, but i n a d d i t i o n , these animals synthesize a v a r i e t y of pheromones w i t h centers of chirality. O b v i o u s l y , i t would be h i g h l y adaptive f o r these arthropods to both e x h i b i t great o l f a c t o r y a c u i t y i n the presence of f l o r a l enantiomers and great s e n s i t i v i t y to t h e i r own o p t i c a l l y a c t i v e pheromones. I t appears t h a t t h i s i s p r e c i s e l y the case. Honeybee workers can be t r a i n e d to e a s i l y d i s c r i m i n a t e between enantiomeric p a i r s which are both congruous and i n c o n gruous odorants f o r human beings (156). S i g n i f i c a n t l y , these i n s e c t s can "memorize" the information encoded i n these s p e c i f i c s i g n a l s and thus respond r a p i d l y to them i f l a t e r encountered. R i l e y et aj_. (157) i d e n t i f i e d S-(+)-4-methyl-3-heptanone as the alarm pheromone of A t t a texana and reported t h a t i t was 100X more a c t i v e as an alarm r e l e a s e r than the unnatural (-)-enantiomer. S i m i l a r l y , Benthuysen and Blum (158) demonstrated t h a t workers of Pogonomyrmex badius were more s e n s i t i v e to the S(+) enantiomer than to the R - ( - ) enantiomer of t h i s compound, which i s the primary alarm pheromone of t h i s s p e c i e s . Iwaki et al_. (159) synthesized the enantiomers of the gypsy moth sex pheromone, ç i s - 7 , 8 - e p o x y - 2 - m e t h y l o c t a d e c a n e ( d i s p a r l u r e ) , and observed t h a t the (7R,8S)-(+)-isomer was f a r more a c t i v e as a sex pheromone than the (7S,8R)-isomer. EAG measurements i n d i c a t e d t h a t the male moths were about 1000X more s e n s i t i v e to the (+)-isomer than the (-) enantiomer of d i s p a r l u r e . A racemic mixture e x h i b i t e d the expected a c t i v i t y of the a c t i v e enantiomer. In c o n t r a s t , Tumlinson et a K (52) noted t h a t the a t t r a c t a n t a c t i v i t y of ( R , Z ) - 5 - ( l - d e c e n y l ) d i h y d r o - 2 ( 3 H ) - f u r a n o n e , ( X ) , the sex pheromone of the Japanese b e e t l e , was almost completely destroyed by as l i t t l e as 10% of (S,Z) enantiomer. Some of the aggregation pheromones of s c o l y t i d beetles a l s o appear to be synthesized w i t h great c h i r a l s p e c i f i c i t y . The f l i g h t response of both sexes of the western pine b e e t l e Dendroctonus brevicomis to ( l R , 5 S , 7 R ) - ( + ) - e x o - b r e v i c o m i n (XX), host terpenes, and racemic f r o n t a l i n (XXI) was much g r e a t e r than the response when the antipode of brevicomin was s u b s t i t u t e d (160). S i m i l a r l y , ( l S , 5 R ) - ( - ) - f r o n t a l i n was a much more powerful a t t r a c t a n t than i t s antipode when t e s t e d i n admixture with

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racemic brevicomin and monoterpenes from the pine t r e e . In con­ t r a s t , the ambrosia b e e t l e , Gnathotrichus s u l c a t u s , which u t i l i z e s a 65:35 r a t i o of the S-(+) and R-(-) enantiomers of 6-methyl-5-hepten-2-ol as an a t t r a c t a n t ( 6 9 ) , e x h i b i t s a syner­ g i s t i c response to enantiomeric mixtures and i s only weakly a t t r a c t e d to the s i n g l e isomers (161). These r e s u l t s c l e a r l y demonstrate t h a t i n s e c t s possess c h i r a l chemoreceptors which have enabled them to e x p l o i t chemical s i g n a l s with maximum a c u i t y and s e n s i t i v i t y . I t i s probable that the o l f a c t o r y world of i n s e c t s w i l l be found to be charac­ t e r i z e d by a d i v e r s i t y of c h i r a l s p e c i f i c i t i e s which have maximized t h e i r responsiveness as t a r g e t s f o r enantiomeric s i g n a l molecules. Pheromones as Pest Control Agents:

A Brave New World

The e f f e c t i v e u t i l i z a t i o n of pheromones f o r pest management w i l l r e q u i r e a d e t a i l e d comprehension of the biology of the t a r g e t s p e c i e s . Shorey et_ a^.. (2) have provided r e a l optimism f o r a n t i c i p a t i n g t h a t an e f f e c t i v e program f o r c o n t r o l of the pink bollworm w i l l be r e a l i z e d i n the f o r s e e a b l e f u t u r e . This imaginative undertaking was made p o s s i b l e by exhaustive s t u d i e s on the biology of the pink bollworm and the concept of c o n t r o l by a i r - p e r m e a t i o n with gossyplure i s an outgrowth of these b i o l o g i c a l i n v e s t i g a t i o n s . Although there has been great impatience with the slow progress i n t h i s f i e l d , necessary s t u d i e s on the b i o ecology of i n s e c t s such as the cabbage l o o p e r , b o l l w e e v i l , bark b e e t l e s , gypsy moth, redbanded l e a f r o l l e r , and the European corn borer promise to provide the background information required to make i t p o s s i b l e to manipulate pest populations w i t h i d e n t i f i e d pheromones. Insects are remarkably adaptive a n i m a l s , but there are good grounds f o r concluding that enlightened c o n t r o l programs u t i l i z i n g pheromones or t h e i r analogs w i l l e v e n t u a l l y succeed i n reducing s e l e c t e d pest populations to manageable l e v e l s . Ulti­ mately, i n s e c t pheromones may provide man w i t h the seeds of d e s t r u c t i o n f o r h i s c h i e f competitors by b r i n g i n g death to arthropods instead of sex. Acknowledgements I am g r a t e f u l to Drs. W. S. Bowers and J . H. Tumlinson f o r p r o v i d i n g me w i t h t h e i r unpublished data on i n s e c t pheromones.

Literature Cited (1) Butenandt, Α., Beckmann, R., Stamm, D., Hoppe-Seyler's Z. Physiol. Chem. (1961), 324, 84. (2) Shorey, Η. H., Gaston, L. K., Kaae, R. S., in "Pest Manage­ ment with Insect Sex Attractants", ACS Symp. Ser., No. 23, Beroza, M., Ed., pp. 67-74, Washington, D.C., 1976.

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(3) Jacobson, Μ., "Insect Pheromones", Academic Press, New York, 1972. (4) Birch, M. C., Ed., "Pheromones", American Elsevier Publ. Co., New York, 1974. (5) Blum, M. S., Brand, J. M., Amer. Zool. (1972), 12, 553. (6) MacConnell, J. G., Silverstein, R. Μ., Ang. Chemie, Int. Ed. (1973), 12, 644. (7) Beroza, Μ., Ed. "Chemicals Controlling Insect Behavior", Academic Press, New York, 1970. (8) Wood, D. L., Silverstein, R. Μ., Nakajima, Μ., Eds., "Control of Insect Behavior by Natural Products", Academic Press, New York, 1970. (9) Tahori, Α., Ed., "Chemical Releasers in Insects", Gordon and Breach, New York, 1971. (10) Roelofs, W. L., Comeau, Α., in "Chemical Releasers in Insects), Tahori, Α., Ed., pp. 91-114,Gordon and Breach New York, 1971. (11) Silverstein, R. Μ., Rodin, J. O., Wood, D. L., Science (1966), 154, 509. (12) Wood, D. L., Browne, L. E., Bedard, W. D., Tilden, P. E., Silverstein, R. Μ., Rodin, J. O., Science (1968), 159, 1373. (13) Wood, D. L., Stark, R. W., Silverstein, R. Μ., Rodin, J. O., Nature (1967), 215, 206. (14) Blum, M. S., Bull. Ent. Soc. Am. (1974), 20, 30. (15) Roelofs, W. L., Comeau, Α., J. Insect Physiol. (1971), 17, 1969. (16) Roelofs, W. L., Comeau, Α., H i l l , Α., Milicevic, G., Science (1971), 174, 297. (17) McDonough, L. Μ., George, D. Α., Butt, Β. Α., Ruth, J. Μ., H i l l , K. R., Science (1972), 177, 177. (18) McDonough, L. M., Moffitt, H. R., Science (1974), 183, 978. (19) Beroza, Μ., Bierl, Β. Α., Moffitt, H. R., Science (1974), 183, 89. (20) Klun, J. Α., Robinson, J. F., Ann. Ent. Soc. Am. (1972), 65, 1337. (21) Klun, J. Α., Chapman, O. L., Mattes, K. C., Wojtkowski, P. W., Beroza, Μ., Sonnet, P. E . , Science (1973), 181, 661. (22) Beroza, Μ., Muschik, G. Μ., Gentry, C. R., Nature, New Biol. (1973), 244, 149, (23) Roelofs, W. L., Cardé, R. T., Tette, J., Environ. Ent. (1973), 2, 252. (24) Shorey, H., in "Control of Insect Behavior by Natural Products", Wood, D. L., Silverstein, R. M., Nakajima, Μ., Eds., pp. 249-284, Academic Press, New York, 1970. (25) Matsumura, F., Coppel, H. C., Tai, Α., Nature (1968), 219, 963. (26) Howard, R., Matsumura, F., Coppel, H. C., J. Chem. Ecol. (1976), 2, 147. (27) Birch, A. J., Brown, W. V., Corrie, J. E. T . , Moore, B. P., J. Chem. Soc. Perkin Trans. I (1972), 1972, 2653.

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(28) Patil, V. D., Nayak, V. R., Dev., S., Tetrahedron (1973), 29, 341. (29) Moore, B. P., J. Insect Physiol. (1968), 14, 33. (30) Nishida, R., Fukami, Η., Ishii, S., Appl. Ent. Zool. (1975), 10, 10. (31) Persoons, C. J., Ritter, F. J., Lichtendonk, W. J., Proc. Kon. Ned. Akad. v. Wetensch., Amsterdam-C (1974), 77, 201. (32) Persoons, C. J., Verwiel, P. E. J., Ritter, F. J., Talman, E . , Nooijen, P. J. F., Nooijen, W. J., Tetrahedron Lett. (1976), 24), 2055. (33) Tahara, S., Yoshida, Μ., Muzitani, J., Kitamura, C., Takahashi, S., Agr. Biol. Chem. (1975), 39, 1517. (34) Nolte, D. J., Eggers, S. H., May, I. R., J. Insect Physiol. (1973), 19, 1547. (35) Bowers, W. S., Nault, L. R., Webb, R. E., Dutky, S. R., Science (1972), 177, 1121. (36) Wientjens, W.H. J. Μ., Lakwijk, A. C., van der Marel, T . , Experientia (1973), 29, 658. (37) Nault, L. R., Montgomery, M. E., Bowers, W. S., Science (1976), 192, 1349. (38) Nishino, C., Bowers, W. S., Nault, L. R., personal communi­ cation (1976). (39) Calam, D. H., Youdeowei, Α., J. Insect Physiol. (1968), 14, 1147. (40) Levinson, Η. Ζ . , Bar Ilan, A. R., Experientia (1971), 27, 102. (41) Aldrich, J. R., Blum, M. S., Duffey, S. S., Fales, Η. Μ., J. Insect Physiol. (1976), in press. (42) Carlson, D. Α., Mayer, M. S., Silhacek, D. L . , James, J. D., Beroza, Μ., Bierl, Β. Α., Science (1971), 174, 76. (43) Mansingh, Α., Steele, R. W., Smallman, Β. N., Meresz, O., Mozogai, C., Can. Ent. (1972), 104, 1963. (44) Richter, I., Naturwissen. (1974), 61, 365. (45) Richter, I., Krain, H., Mangold, Η. Κ., Experientia (1976), 32, 186. (46) Uebel, E. C., Sonnet, P. Ε . , Miller, R. W., Beroza, M., J. Chem. Ecol. (1975), 1, 195. (47) Uebel, E. C., Sonnet, P. Ε . , Bierl, Β. Α., Miller, R. W., J. Chem. Ecol. (1975), 1, 377. (48) Jacobson, Μ., L i l l y , C. E., Harding, C., Science (1968), 159, 208. (49) Horler, D. F., J. Chem. Soc. C (1970), 1970, 859. (50) Henzell, R. F., Lowe, M. D., Science (1970), 168, 1005. (51) Hoyt, C. P., Osborne, G. O., Mulcock, A. P., Nature (1971), 230, 472. (52) Tumlinson, J. H., Klein, M. G., Doolittle, R. E . , Ladd, Jr., T. L., personal communication (1976). (53) Klein, M. G., Ladd, Jr., T. L., Lawrence, K. O., Environ. Ent. (1972), 1, 397.

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(54) Tumlinson, J. H . , Hardee, D. D., Gueldner, R. C . , Science (1969), 166, 1010. (55) Silverstein, R. Μ., Rodin, J. B., Burkholder, W. E., Gorman, J. Ε . , Science (1967), 157, 85. (56) Fukui, H . , Matsumura, F . , Ma, M. C . , Burkholder, W. E., Tetrahedron Lett. (1974), 40, 3563. (57) Rodin, J. O., Silverstein, R. Μ., Burkholder, W. E., Gorman, J. E . , Science (1969), 165, 904. (58) Yarger, R. G . , Silverstein, R. Μ., Burkholder, W. E., J. Chem. Ecol. (1975), 1, 323. (59) V i t é , J. P., Renwick, J. Α. Α . , J. Insect Physiol. (1971), 17, 1699. (60) Renwick, J. Α. Α . , V i t é , J. P . , J. Insect Physiol. (1972), 18, 1215. (61) Silverstein, R. M . , Brownlee, R. G . , Bellas, T. E., Wood, D. L . , Browne, L. E . , Science (1968), 159, 889. (62) Kinzer, G. W., Fentiman, J r . , A. F . , Page, J r . , T. F . , Foltz, R. L . , V i t é , J. P., Pitman, G. B., Nature (1969), 221, 477. (63) Wood, D. L . , in van Emden, H. F . , E d . , "Insect Plant Relationships", pp. 101-117, Symp. Roy. Ent. Soc. (London) 6, 1972. (64) Renwick, J. Α. Α . , V i t é , J. P., Nature (1969), 224, 1222. (65) Pitman, G. Β., Vite, J. P., Ann. Ent. Soc. Am. (1970), 63, 661. (66) Kinzer, G. W., Fentiman, J r . , A. F . , Foltz, R. L . , Rudinsky, J. Α . , J. Econ. Ent. (1971), 64, 970. (67) V i t é , J. P., Pitman, G. B., Fentiman, J r . , A. F . , Kinzer, G. W., Naturwissen. (1972), 59, 469. (68) Borden, J. H . , in Birch, M. C . , E d . , "Pheromones", pp. 135160, American Elsevier Publ. Co., New York, 1974. (69) Byrne, K. J . , Swigar, Α. Α . , Silverstein, R. Μ., Borden, J. H . , Stokkink, E . , J. Insect Physiol. (1974), 20, 1895. (70) Pearce, G. T . , Gore, W. Ε., Silverstein, R. M . , Peacock, J. W., Cuthbert, R. Α . , Lanier, G. N . , Simeone, J. B., J. Chem. Ecol. (1975), 1, 115. (71) Roelofs, W. L., Cardé, R. T . , in Birch, M. C . , E d . , "Pheromones", pp. 96-114, American Elsevier Publ. Co., New York, 1974. (72) Kennedy, J. S., J. Aust. Ent. Soc. (1972), 11,168. (73) Weatherston, J . , Roelofs, W., Comeau, Α . , Sanders, C. J . , Can. Ent. (1971), 103, 1741. (74) Weatherston, J . , MacLean, W., Can. Ent. (1974), 106, 281. (75) Roelofs, W. L., Hill, A. S., Cardé, R. T . , Baker, T. C . , Life Sci. (1974), 14, 1555. (76) Tumlinson, J. H . , Hendricks, D. E . , Mitchell, E. R., Doolittle, R. Ε . , Brennan, M. M . , J. Chem. Ecol. (1975), 1, 203. (77) Nesbitt, B. F . , Beevor, P. S., H a l l , D. R., Lester, R., Dyck, V. Α . , J. Insect Physiol. (1975), 21, 1883.

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(78) Bierl, Β. Α., Beroza, Μ., Collier, C. W., Science (1970), 170, 87. (79) Kasang, G., Schneider, D., Beroza, Μ., Naturwissen. (1974), 61, 130. (80) Kasang, G., Knauer, B., Beroza, Μ., Experientia (1974), 30, 147. (81) Roelofs, W. L., Cardé, R. T., Science (1971), 171, 684. (82) Smith, R. G., Daterman, G. E., Daves, Jr., G. D., Science (1975), 188, 63. (83) Henderson, H. E., Warren, F. L. Augustyn, O. P. H., Burger, Β. V., Schneider, D. F., Boshoff, P. R., Spies, H. S. C. Geertsema, H., Chem. Comm. (1972), 1972, 686. (84) Kochansky, J., Tette, J., Taschenberg, E. F., Cardé, R. T . , Kaissling, K.-E., Roelofs, W. L . , J. Insect Physiol. (1975), 21, 1977. (85) Hummel, H. E., Gaston, L. Κ., Shorey, H. H., Kaae, R. S., Byrne, K. J., Silverstein, R. Μ., Science (1973), 181, 873. (86) Tamaki, Y., Noguchi, H., Yushima, T . , Hirano, C., Appl. Ent. Zool. (1971), 6, 139. (87) Tamaki, Y., Noguchi, H., Yushima, T . , Hirano, C., Honma, K., Sugawara, H., Kontyû(1971), 39, 338. (88) Meijer, G. Μ., Ritter, F. J., Persoons, C. J., Minks, Α. Κ., Voerman, S., Science (1972), 175, 1469. (89) Nesbitt, B. F., Beevor. P. S., Cole, R. Α., Lester, R., Poppi, R. G., Nature, New Biol. (1973), 244, 208. (90) Tamaki, Y., Yushima, T . , J. Insect Physiol. (1974), 20, 1005. (91) Tamaki, Y., Noguchi, H., Yushima, T . , Appl. Ent. Zool. (1973), 8, 200. (92) Brady, U. Ε . , Tumlimson, J. H., Brownlee, R. G., Silverstein, R. Μ., Science (1971), 171, 802. (93) Kuwahara, Y., Kitamura, C., Takahashi, S., Hara, H., Ishii, S., Fukami, H., Science (1971), 171, 801. (94) Brady, U. E . , Life Sci. (1973), 13, 227. (95) Ganyard, Jr., M. C., Brady, U. E., Nature (1971), 234, 415. (96) Tumlinson, J. H., Yonce, C. E., Doolittle, R. E . , Heath, R. R., Gentry, C. R., Mitchell, E. R., Science (1974), 185, 614. (97) Roelofs, W., H i l l , Α., Cardé, R., Tette, J., Madsen, H., Vakenti, J., Environ. Ent. (1974), 3, 747. (98) Dahm, Κ. H., Meyer, D., Finn, W. E., Reinhold, V . , Röller, H., Naturwissen. (1971), 58, 265. (99) Röller, Η., Biemann, Κ., Bjerke, J. S., Norgard, D. W., McShan, W. H., Acta Ent. Bohem. (1968), 65, 208. (100) Leyrer, R. L., Monroe, R. E., J. Insect Physiol. (1973), 19, 2267. (101) Birch, M. C., in Birch, M. C., "Pheromones", pp. 115-134, American Elsevier Publ. Co., New York, 1974. (102) Aplin, R. T . , Birch, M. C., Experientia (1970), 26, 1193.

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CENTURY

(103) Meinwald, J., Meinwald, Y. C., J. Am. Chem. Soc. (1966), 88, 1305. (104) Meinwald, J., Meinwald, Y. C., Mazzocchi, P. H., Science (1969), 164, 1174. (105) Schneider, D., Seibt, U . , Science (1969), 164, 1173. (106) Pliske, T. E . , Eisner, T . , Science (1969), 164, 1170. (107) Meinwald, J., Chalmers, Α. Μ., Pliske, T. E . , Eisner, T . , Tetrahedron Lett. (1968), 1968, 4893. (108) Meinwald, J., Chalmers, Α. Μ., Pliske, T. E . , Eisner, T . , Chem. Comm. (1969), 1969, 86. (109) Meinwald, J., Thompson, W. R., Eisner, T . , Owen, D. F., Tetrahedron Lett. (1971), (38), 3485. (110) Edgar, J. Α., Culvenor, C. C. J., Robinson, G. S., J. Aust. Ent. Soc. (1973), 12, 144. (111) Edgar, J. Α., Culvenor, C. C. J., Nature (1974), 248, 614. (112) Culvenor, C. C. J., Edgar, J. Α., Experientia (1972), 28, 627. (113) Lundgren, L., Bergström,. G., J. Chem. Ecol. (1975), 1, 399. (114) Pavan, Μ., Ronchetti, G., Atti Soc. Ital. Sci. Nat. Mus. Stor. Nat. Milano (1955), 94, 379. (115) Blum, M. S., in Beroza, M., Ed., "Chemicals Controlling Insect Behavior", pp. 61-94, Academic Press, New York, 1970. (116) Ayre, G. L . , Blum, M. S., Physiol. Zool. (1971), 44, 77. (117) Blum, M. S., Warter, S. L., Monroe, R. S., Chidester, J. C., J. Insect Physiol. (1963), 9, 881. (118) Trave, R., Pavan, Μ., Chim. Ind., Milano (1956), 38, 1015. (119) Cavill, G. W. Κ., Hinterberger, H., Proc. 11th Int. Congr. Ent. (1960), 3, 53. (120) Crewe, R. Μ., Blum, M. S., J. Insect Physiol. (1972), 18, 31. (121) McGurk, D. J., Frost, J., Eisenbraun, E. J., Vick, Κ., Drew, W. Α., Young, J., J. Insect Physiol. (1966), 12, 1435. (122) Fales, Η. Μ., Blum, M. S., Crewe, R. Μ., Brand, J. M., J. Insect Physiol. (1972), 18, 1077. (123) Ghent, R. L . , "Adaptive Refinements in the Chemical Defen­ sive Mechanisms of Certain Formicinae", Ph.D. Thesis, Cornell Univ., 1961. (124) Maschwitz, U., Z. Vergl. Physiol. (1964), 47, 596. (125) Regnier, F. Ε . , Wilson, Ε. O., J. Insect Physiol. (1968), 14, 955. (126) Wheeler, J. W., Blum, M. S., Science (1973), 182, 501. (127) Duffield, R. Μ., Blum, M. S., Wheeler, J. W., Comp. Biochem. Physiol. (1976), 54B, 439. (128) Wheeler, J. W., Evans, S. L., Blum, M. S., Torgerson, R. L . , Science (1975), 187, 254. (129) Duffield, R. Μ., Blum., M. S., Experientia (1975), 31, 466. (130) Blum, M. S., Crewe R. Μ., Kerr, W. E . , Keith, L. H., Garrison, A. W., Walker, Μ. Μ., J. Insect Physiol. (1970), 16, 1637.

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12.

BLUM

Insect Pheromones

235

(131) Shearer, D. Α., Boch, R., Nature (1965), 206, 530. (132) Boch, R., Shearer, D. Α., Stone, B. C., Nature (1962), 195, 1018. (133) Tumlinson, J. H., Silverstein, R. Μ., Moser, J. C., Brownlee, R. G., Ruth, J. Μ., Nature (1971), 234, 348. (134) Ritter, F. J., Rotgans, I. Ε. M., Talman, E., Verwiel, P. E. J., Stein, F., Experientia (1973), 29, 530. (135) Huwyler, S., Grob, Κ., Viscontini, M., J. Insect Physiol. (1975), 21, 299. (136) Kerr, W. E., Blum, M. S., Fales, Η. Μ., unpublished data. (137) Gary, Ν. E., Science (1962), 136, 773. (138) Jewett, D. Μ., Matsumura, F., Coppel, H. C., Science (1976), 192, 51. (139) Butler, C. G., Callow, R. Κ., Johnston, N. C., Proc. Roy. Soc. Lond. Β (1961), 155, 417. (140) Butler, C. G., Fairey, Ε. Μ., J. Apic. Res. (1963), 2, 14. (141) Butler, C. G., Gibbons, D. Α., J. Insect Physiol. (1958), 2, 61. (142) Ikan, R., Gottlieb, R., Bergmann, E. D., Ishay, J.,J.Insect Physiol. (1969), 15, 1709. (143) Blum, M. S., Ann. Ent. Soc. Am. (1966), 59, 962. (144) Régnier, F. Ε . , Wilson, Ε. O., Science (1971), 172, 267. (145) Kullenberg, B., Bergström, G., Stallberg-Stenhagen, S., Acta Chem. Scand. (1970), 24, 1481. (146) Velthuis, H. H. W., de Camargo, J. M. F., Z. Tierpsychol. (1975), 38, 409. (147) Wheeler, J. W., Evans, S. L., Blum, M. S., Velthuis, H. H. W., de Camargo, J. M. F., unpublished data. (148) Hölldobler, B., Maschwitz, U., Z. Vergl. Physiol. (1965), 50, 551. (149) Brand, J. Μ., Duffield, R. M., MacConnell, J. G., Blum, M. S., Fales, Η. Μ., Science (1973), 179, 388. (150) Brand, J. Μ., Fales, Η. Μ., Sokoloski, Ε. Α., MacConnell, J. G., Blum, M. S., Duffield, R. Μ., Life Sci (1973), 13, 201. (151) Lloyd, Η. Α., Blum, M. S., Duffield, R. Μ., Insect Biochem. (1975), 5, 489. (152) Crewe, R. Μ., Fletcher, D. J. C., J. Ent. Soc. South Afr. (1974), 37, 291. (153) Casnati, G., Ricca, Α., Pavan, Μ., Chim. Ind., Milano (1967), 49, 57. (154) Wilson, E. O., Psyche (1958), 65, 41. (155) Blum, M. S., Warter, Ann. Ent. Soc. Am. (1966), 59, 774. (156) Lensky, Y., Blum., M. S., Life Sci. (1974), 14, 2045. (157) Riley, R. G., Silverstein, R. Μ., Moser, J. C., Science (1974), 183, 760. (158) Benthuysen, J. L., Blum, M. S., J. Ga. Ent. Soc. (1974), 9, 235. (159) Iwaki, S., Marumo, S., Saito, T., Yamada, Μ., Katagiri, Κ., J. Am. Chem. Soc. (1974), 96, 7842.

236

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(160) Wood, D. L., Browne, L. Ε . , Ewing, B., Lindahl, Κ., Bedard, W. D., Tilden, P. Ε . , Mori, Κ., Pitman, G. B., Hughes, P. R., Science (1976), 192, 896. (161) Borden, J. H., Chong, L., McLean, J. Α., Slessor, Κ. Ν., Mori, Κ., Science (1976), 192, 894.

13 Benzoylphenyl Ureas—A New Group of Larvicides Interfering with Chitin Deposition A. VERLOOP Research Laboratories, Philips-Duphar B.V., The Netherlands

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch013

C. D. F E R R E L L Thompson-Hayward Chemical Co., Kansas City, Kan. 66110

The development of s e l e c t i v e crop p r o t e c t i o n compounds based on the interference with c h i t i n deposition i n fungi and i n s e c t s has been one of the aims i n p e s t i c i d e design for several decades. A major development i n t h i s area was the discovery of the mode of a c t i o n of the f u n g i c i d a l a n t i b i o t i c polyoxin D by Misato et al. i n the period of 1 9 6 8 1970 (1)· In these and subsequent studies the Japanese group c l e a r l y demonstrated that polyoxin D and r e l a t e d compounds i n t e r f e r e d with c h i t i n synthesis i n several fungi by i n h i b i t i n g c h i t i n synthetase, the ultimate enzyme i n the b i o s y n t h e t i c pathway. This i s i l l u s t r a t e d i n Figure 1 where the l a s t part of t h i s pathway i s given. Other Japanese workers (2) found that the synthetic phosphorus-containing compound kitazin also prevented the i n c o r p o r a t i o n of UDP-N-acetylglucosamine i n chitin. However t h e i r further studies revealed that i n t h i s case the primary a c t i o n was probably not on chitin synthetase itself but that k i t a z i n prevented the permeation of the substrate through the cytoplasmic membrane so that it was unable to reach the target enzyme (Figure 1 ) . In contrast to the s i t u a t i o n mentioned i n respect to f u n g i c i d a l a c t i v i t y , no i n s e c t i c i d e s were described i n the l i t e r a t u r e prior to 1 9 7 0 , the activity of which was based on interference with chitin formation. Now, i n the course of i n v e s t i g a t i o n s centered on the Philips-Duphar h e r b i c i d e d i c h l o b e n i l the d e r i v a t i v e Du 19111 (I) was prepared.

237

238

FUNGICIDES

PESTICIDE C H E M I S T R Y I N T H E 2 0 T H C E N T U R Y

INTERFERING WITH CHITIN FORMATION

UDP- Ν - acetylglucosamine (κ)

• I γ

Permeation through cytoplasmic membrane

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch013

U D P - N - acetylglucosamine @

• ^

Chitin synthetase

Chitin ®

POLYOXIN

D Ο COOH

HOOÇ ÇOHNCH

/Ο

HoNCH

I HÇOH CH OCONH2 2

©

OH

OH

KITAZIN

(C^HgO^- Ρ - S - C H Ο Figure 1.

2

13.

VERLOOP

AND

Benzoylphenyl

FERRELL

CI

CI C II

Cl

239

Ureas

0

-

Ν I

-

C II

0

Η

Ν

Cl

Η

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch013

(I)

D u r i n g the s c r e e n i n g p r o g r a m no h e r b i c i d a l or phytotoxic e f f e c t s were f o u n d , b u t i t was observed that larvae of several insects, including Pieris brassicaejshowed a b n o r m a l s y m p t o m s some 5 o r 6 days a f t e r i n g e s t i o n of the compound. The l a r v a e stopped f e e d i n g and hung from the l e a v e s , suggesting that they were starting to m o u l t . But i n s t e a d of s h e d d i n g their exuviaethey turned b l a c k and d i e d . Closer examination r e v e a l e d that the a p o l y s e d larvae were moving within t h e i r intact exuviae but that they were t o t a l l y or p a r t l y u n a b l e to shed these exuviae and to w r i g g l e out (^). H i s t o l o g i c a l examination of affected larvae revealed severe lesions i n the endocuticular tissue. Hence the newly formed cuticle h a d to be a v e r y d e l i c a t e one, u n a b l e to r e s i s t the muscular traction and the i n c r e a s e d t u r g o r during moulting, so t h a t a f f e c t e d larvae would not succeed in casting their exuviae(ji ) · S o f t l a r v a l e n d o c u t i c l e consists m a i n l y of c h i t i n and p r o t e i n , integrated as a c o m p l i c a t e d n e t w o r k , so t h a t t h e r e a r e different ways i n w h i c h Du 19111 might affect its formation, i n c l u d i n g an i n f l u e n c e on c h i t i n f o r m a t i o n . Further studies, to be d i s c u s s e d l a t e r , soon revealed that an e f f e c t o n c h i t i n was t h e m o s t p r o b a b l e mode of action. The h i g h i n s e c t i c i d a l a c t i v i t y o f Du 19111 against the l a r v a l stages of s e v e r a l lepidopterous, coleopterous and d i p t e r o u s i n s e c t s and i t s unique mode o f a c t i o n p r o m p t e d u s t o s y n t h é t i s e several hundreds of b e n z o y l p h e n y l u r e a s and to evaluate their i n s e c t i c i d a l potency i n laboratory tests and s m a l l s c a l e f i e l d t r i a l s (4^, ^ , 6) . T h e s e and other studies l e d to the u l t i m a t e choice of diflubenzuron (il) as the o p t i m a l d e r i v a t i v e for further development.

PESTICIDE C H E M I S T R Y IN T H E 2 0 T H C E N T U R Y

240

F

w

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch013

ρ

π

v

r.

v

Ο

Η

Ο

H

w

(II) A f t e r t h e i n t r o d u c t i o n o f d i f l u b e n z u r o n (7.) many a u t h o r s published laboratory and f i e l d studies on i t s i n s e c t i c i d a l spectrum. These studies cannot be d i s c u s s e d i n the context of the present paper. They have been summarized elsewhere (8^, 2., 10, 11) · However, i t is relevant to m e n t i o n t h a t i n several studies, a d d i t i o n a l l y to the l a r v i c i d a l effect of diflubenzuron, a c t i v i t i e s on the eggs of various insect species have been found (j_2, 1k , 15 « 16 ,

17 »

18).These o v i c i d a l effects can e i t h e r be obtained by t o p i c a l a p p l i c a t i o n to the eggs or by f e e d i n g to gravid female insects. In either case the phenomena are s i m i l a r : normal development of the primary stages of the l a r v a e i n the eggs takes place but the organisms are u n a b l e to leave the eggs by r u p t u r i n g them, because again the f o r m a t i o n of the endocuticle is disturbed. This very interesting "broadening" of the i n s e c t i c i d a l spectrum of d i f l u b e n z u r o n has been discussed i n details elsewhere (j^) . A survey of the state of development of d i f l u b e n z u r o n i n the USA has been g i v e n by F e r r e l l and V e r l o o p at the A . C . S . M e e t i n g , A u g u s t 1975 (20): d i f l u b e n z u r o n can be a p p l i e d at v e r y low r a t e s i n agriculture (soybeans, cotton, apple orchards),in forestry, for mosquito and f l y c o n t r o l and p r o b a b l y i n s t o r e d g r a i n . T h e same p a p e r h a s summarised also i t s low t o x i c i t y to mammals a n d t o n o n t a r g e t organisms. In the meantime i t s commercial i n t r o d u c t i o n has begun in some E u r o p e a n c o u n t r i e s and i n Egypt. Registration i n the U . S . A . and commercial i n t r o d u c t i o n by the Thompson-Hayward C h e m i c a l Company i s e x p e c t e d at short notice. However, i t i s not our i n t e n t i o n to discuss further these fascinating p r a c t i c a l p o s s i b i l i t i e s of the b e n z o y l p h e n y l ureas f o r i n s e c t control. In the following part o f t h i s p a p e r we w o u l d r a t h e r discuss the s c i e n t i f i c background of the d i s c o v e r y of diflubenzuron, concentrating on the f o l l o w i n g aspects:

13.

VERLOOP

-

AND

Benzoylphenyl

of

241

Ureas

i t s s e l e c t i o n from the benzoylphenyl i t s fate i n the environment, i t s mode o f a c t i o n .

Selection

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch013

FERRELL

urea

series,

diflubenzuron

A f t e r t h e d i s c o v e r y o f Du 1 9 1 1 1 * many h u n d r e d s of r e l a t e d b e n z o y l p h e n y l ureas were synthetized and screened with respect to larvicidal activity. These e f f o r t s were guided by t h e study o f q u a n t i t a ­ t i v e s t r u c t u r e - a c t i v i t y r e l a t i o n s h i p s (QSAR) f o l l o w i n g t h e Hansch approach. I n t h i s method linear free-energy r e l a t e d and other e l e c t r o n i c , hydrophobic, and steric substituent constants are used f o r a q u a n t i t a t i v e a n a l y s i s o f t h e p o s s i b l e ways i n w h i c h s u b s t i t u e n t s may m o d u l a t e b i o a c t i v i t y i n a c o n g e n e r i c s e r i e s . I n t h e QSAR s t u d i e s o f b e n z o y l p h e n y l u r e a s t h e e l e c t r o n i c Hammett α-constants a n d t h e h y d r o ­ p h o b i c H a n s c h π-constants w e r e u s e d . To m e a s u r e t h e steric influences, steric substituent constants o f a n e w t y p e (Β Ί , B 2 , B 3 , BZj., a n d L ) w e r e applied which had r e c e n t l y been introduced by us and which give improved c o r r e l a t i o n s i n comparison with the steric E constants used i n the l i t e r a t u r e h i t h e r t o (21, 2 2 ) .The c o n s t a n t s B-|toB^ a r e m e a s u r e s o f t h e widths o f substituents i n four rectangular d i r e c t i o n s . The L-constant accounts f o r the length of a s u b s t i ­ tuent . QSAR f o r t h e l a r v i c i d a l e f f e c t s o f b e n z o y l p h e n y l u r e a s on P i e r i s b r a s s i c a e a n d Aëdes a e g y p t i larvae were s t u d i e d f o r t h e f o l l o w i n g subseries; 1. b e n z o y l p h e n y l u r e a s s u b s t i t u t e d i n t h e a n i l i n e ring, 2. benzoylphenyl ureas substituted i n the benzoyl ring, 3. benzoylphenyl ureas substituted i n the "bridge". The p r e s e n t d i s c u s s i o n w i l l be c o n f i n e d m a i n l y t o subseries 1 above and t o t h e r e s u l t s w i t h Pieris b r a s s i c a e . The o t h e r s t u d i e s and a more complete study o f s u b s t i t u e n t s o f t h e a n i l i n e r i n g w i l l be published e l s e w h e r e ( . 2 ^ , 2 ^ + ) .The most significant equations f o r the l a r v i c i d a l a c t i v i t i e s of 2,6-dichlorobenzoylphenyl ureas as functions o f para- and meta-substitution i n the aniline ring were : For para-substituents -Log E D C Q = + ÏÏ + 2.37 α 0 . 2 7 B ^ +0.87 η = 31, r = 0.8^3, s = 0 . ^ 9 9 , F = 15.9^ S

1,10

0.40L -

PESTICIDE C H E M I S T R Y IN T H E 2 0 T H

242

For

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch013

-Log

paraΈΏ

50

and =

CENTURY

meta-substituents

+

0.93

-

1.28L

η

=

48,

τι +

1.89

σ

+

r

0.796,

=

-

0 . 3 ^ L

P

a

r

a

3.36

m e t a

s

=

0.564,

F

=

14.59

In these analyses ED^Q is the concentration required f o r a 509e r e d u c t i o n o f t h e d e v e l o p m e n t o f P i e r i s brassicae L . , η i s the number o f compounds i n the series, r is the correlation c o e f f i c i e n t , s is the standard d e v i a t i o n , and F i s the F - v a l u e which indicates the s i g n i f i c a n c e of the correlation found. From the r e s u l t s given i t can be c o n c l u d e d t h a t the inclusion of meta-substituents leads to essentially the same r e g r e s s i o n e q u a t i o n as the one w i t h o n l y para-substituents. E v i d e n t l y a l l types of substituent influences play a r o l e . The s i g n of the α-term means that e l e c t r o n - w i t h d r a w i n g groups enhance the l a r v i ­ cidal a c t i v i t y , w h i c h was a l s o concluded by Yu and K u h r i n a r e c e n t p a p e r o n QSAR o f t h e l a r v i c i d a l effect of a series of seven 2,6-dichlorobenzoylphenyl ureas on Hylemya p l a t u r a (25 ) · T h e s e a u t h o r s con­ cluded from t h e i r analysis that hydrophobic effects were n e g l i g i b l e . However, i t is quite evident from the present results w i t h the much l a r g e r series that a l s o h y d r o p h o b i c and s t e r i c i n f l u e n c e s manifest themselves. An a n a l y s i s of a l l these effects leads to the conclusion that the substituents s h o u l d be electron attracting, l i p o p h i l i c , "short", and "thick", in order to c o n t r i b u t e m a x i m a l l y to the a c t i v i t y of the molecule ( 2J[) · I n f a c t the experimental a c t i v i t i e s o f the p - C l - and p - I - d e r i v a t i v e s were found to be about 100 t i m e s less than p r e d i c t e d but i n repeated t e s t s the p r e d i c t i o n s were f o u n d to be correct. Further studies r e v e a l e d that i n the f i r s t tests very coarse particles o f t h e s e two d e r i v a t i v e s had been used, w h i l e the t e s t i n g of the other derivatives had been performed with f i n e p a r t i c l e s . This focused attention f o r the f i r s t time on the g r e a t importance of p a r t i c l e s i z e i n the e v a l u a t i o n of the b e n z o y l phenyl ureas. The s e r i e s d i s c u s s e d i n c l u d e d Du 19111 > the f i r s t compound f o u n d , but the analyses indicated t h a t o t h e r d e r i v a t i v e s were more a c t i v e . F r o m two or t h r e e o f the most a c t i v e compounds PH 6 Ο - 3 8 ( i l l ) was c h o s e n b e c a u s e i t was f o u n d t o b e t h e one w h i c h c o u l d be s y n t h e t i z e d most e c o n o m i c a l l y on an i n d u s t r i a l scale. C o n s e q u e n t l y PH 6 Ο - 3 8 was taken f o r p r e l i m i n a r y development b o t h i n the USA and i n Europe. It i s i n t e r e s t i n g to note t h a t PH 6Ο-38 was one o f the compounds r e t e s t e d a f t e r the QSAR studies.

13.

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FERRELL

Benzoylphenyl

243

Ureas

Ν I

Η

Η

~

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch013

(m) However, a t t h i s s t a g e the r e s u l t s o f a n o t h e r a r e a o f our r e s e a r c h o f the b e n z o y l p h e n y l u r e a s , i . e . the e n v i r o n m e n t a l s t u d i e s , were g o i n g to have a v i t a l i n f l u e n c e on the f u r t h e r s e l e c t i o n o f the b e s t compound. A p r e l i m i n a r y s t u d y w i t h a r a d i o a c t i v e p r e p a r a t i o n o f ^ t h e " p a r e n t " compound Du 19111 > labeled with C a t the c a r b o n y l group o f the b e n z o y l ring, r e v e a l e d t h a t t h i s compound was v e r y s t a b l e i n a g r i c u l t u r a l s o i l s : a h a l f l i f e o f more t h a n s i x months was f o u n d . A more e x t e n s i v e s t u d y was c a r r i e d out w i t h the f i r s t c a n d i d a t e f o r development, PH 6 0 - 3 8 , l a b e l e d ( w i t h ^C) at the same p o s i t i o n , A h a l f l i f e i n s o i l s o f 6 - 1 2 months was a g a i n o b t a i n e d . I t was a l s o found t h a t 2 , 6 - d i c h l o r o b e n z a m i d e was the p r i n c i p a l l a b e l e d m e t a b o l i t e . Now t h e r e a r e s e v e r a l p o s s i b l e r o u t e s f o r the h y d r o l y s i s o f the b e n z o y l p h e n y l u r e a s , as i s i l l u s t r a t e d i n F i g u r e 2, where r o u t e A would l e a d to o r t h o - s u b s t i t u t e d b e n z o i c a c i d s and p - c h l o r o - p h e n y l u r e a w h i l e r o u t e s 2 and 3 would b o t h r e s u l t i n o r t h o - s u b s t i t u t e d benzamides and p - C l - a n i l i n e as the p r i m a r y c o n v e r s i o n p r o d u c t s . E v i d e n t l y r o u t e s 2 o r 3 were the p r e f e r r e d ones i n the case o f PH 6 Ο - 3 8 w i t h X = CI (28). The f a c t t h a t r o u t e 1 was o f minor i m p o r t a n c e i n the case o f X = CI was f a m i l i a r to us b e c a u s e o r our e a r l i e r work on the f a t e o f our h e r b i c i d e d i c h l o b e n i l , or 2 , 6 - d i c h l o r o b e n z o n i t r i l e , i n s o i l s . D i c h l o b e n i l i s degraded q u i t e e a s i l y i n t o 2,6d i c h l o r o b e n z a m i d e , but t h i s compound, BAM, i s very s t a b l e i n s o i l s w i t h a h a l f l i f e o f a t l e a s t two y e a r s , as i s i l l u s t r a t e d i n F i g u r e 3 (.26, 27 ) * We knew t h a t a s h i f t o f a t l e a s t one c h l o r i n e atom from the o r t h o - p o s i t i o n to the meta- o r p a r a p o s i t i o n r e s u l t e d i n much more s o i l - d e g r a d a b l e benzamides but t h i s c o u l d not be a p p l i e d h e r e , because we had l e a r n e d from o t h e r QSAR s t u d i e s w i t h the b e n z o y l p h e n y l u r e a s mentioned e a r l i e r t h a t the 2 , 6 - p o s i t i o n o f t h e ( c h l o r i n e ) s u b s t i t u e n t s was essential for a high l a r v i c i d a l a c t i v i t y . However, we a l s o knew t h a t the s m a l l e r f l u o r i n e atoms would s t i l l p e r m i t o f a h i g h r a t e o f h y d r o 1

PESTICIDE C H E M I S T R Y IN T H E 2 0 T H C E N T U R Y

244

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch013

N-Lc-Î-N-/~~Vci w

(

1

x

Ç> ^ y C O O H

+

HgN-C-N-^^-CI

/A

2,3 [J> ^ ~ ^ - C O N H + H N — ^ ~ ^ C I + C Q 2

2

2

X=CI, Major route 2,3; PH 60-38 X = F, Figure 2.

Major route 1 ; dif lubenzuron

Possibilities of the hydrolytic cleavage of 2,6-substituted benzoylphenyl urea

13.

VERLOOP

AND

FERRELL

Benzoylphenyl

Ureas

l y s i s o f 2,6-difluorobenzamide i nsoils, h a l f l i f e o f 2-3 w e e k s , a s i s i l l u s t r a t e d

8-10

\ / · _ ,^\V Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch013

\z=(

* Figure 3.

N HΛΤΤΤ0 2 - 3 w e e k s

Ο VTT

2

OH

weeks"

245

with a i nFigure

3·

Further degradation

Further

4-6 weeks' d e g r a d a t i o n

F Degradation of 2,6-dichlorobenzamide in the soil

(BAM) and 2,6-difluorobenzamide

On p u t t i n g o n e a n d o n e t o g e t h e r t h e s y n t h e s i s o f t h e f l u o r i n e a n a l o g u e o f PH 60-38 s u g g e s t e d i t s e l f as a p o s s i b l e means o f o b t a i n i n g a h i g h e r r a t e o f d e g r a d a t i o n i n s o i l s v i a r o u t e 1. T h i s i d e a proved very f r u i t f u l : thepredictions o f a faster deg r a d a b i l i t y and o f t h eprimary metabolic pathway of t h e f l u o r i n e analogue, PH 6θ-4θ o r d i f l u b e n z u r o n ( i l ) , i n s o i l s were b o t h found t o be c o r r e c t . M o r e o v e r , t h e l a r v i c i d a l a c t i v i t y o f t h e new d e r i v a t i v e was a p p r e c i a b l y h i g h e r than t h a t o f PH 6Ο-38, w h i c h was a c o m p l e t e a n d p l e a s a n t sur­ prise f o r us a t that time. Of c o u r s e t h i s new f i n d i n g i n i t i a t e d t h e s y n t h e s i s o f a l a r g e number o f 2 , 6 - d i f l u o r o b e n z o y l p h e n y l u r e a s a n d a g a i n QSAR w a s u s e d f o r t h e o p t i m i s a t i o n o f t h e s e r i e s . A combined a n a l y s i s of t h e 2,6-difluorobenzoyl and 2,6-dichlorobenzoyl s u b s e r i e s (iv) was p e r f o r m e d b o t h a s a f u n c t i o n of v a r i a t i o n o f the substitution pattern i n the aniline ring.

(IV)

PESTICIDE C H E M I S T R Y I N T H E 2 0 T H C E N T U R Y

246

The d i f f e r e n c e s i n t h e two s u b s e r i e s are accounted f o r w i t h t h e a i d o f t h e dummy p a r a m e t e r which was made z e r o i n t h e 2 , 6 - d i c h l o r o b e n z o y l subseries (R-j = C l ) a n d u n i t y i n t h e 2 , 6 - d i f l u o r o b e n z o y l subseries (R-j = F ) . I n t h i s a n a l y s i s a l s o a number o f compounds were i n c l u d e d i n w h i c h t h e a n i l i n e n i t r o g e n was s u b s t i t u t e d w i t h a m e t h y l g r o u p ; here t h e dummy p a r a m e t e r was u s e d , w i t h U£ = 0 i f R = H , and = 1 i f R = CH^. The resulting regression equations were: F o r R^ = para-substituents 2

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch013

-Log

2

ED^

0

+

1.40D η

For -Log

R^ = m e t a ED

π + 2 . 3 5 σ - 0.40L

=+1.10

0.70D

= 48, r and

-

0 . 2 4

-

0.61D

B

0.27B^

+ 0.84

2

= 0.909,

5 = 0.408,

F = 32.63

para-substituents π + 1.99

= + 0 . 9 5

η

-

1

-

z

+

2

= 70,

p

a

r

a

-

σ 1 .

3

0 L

0 . 3 4 L m

e

t

a

+

p

a

r

a

1.40

D L

+ 3.38 r

= 0.892,

s

= 0.535,

F =

34.37

It can be concluded that these equations are very similar to the equations discussed earlier f o rt h e 2,6-dichlorobenzoyl subseries as f a r as the elec­ tronic, hydrophobic, andsteric influences are concerned. Thec o e f f i c i e n t s o f t h e dummy p a r a m e t e r s lead to the conclusion that the 2,6-difluorobenzoyl subseries i s about 25 t i m e s more a c t i v e on Pieris brassicae than the 2,6-dichlorobenzoyl series, whereas methyl substitution at the a n i l i n e nitrogen systematically decreases the activity by a factor of about f i v e ( 2 3 ) . The s i m i l a r i t i e s i n t h e i n f l u e n c e s o f t h e d i f f e r e n t parameters i n t h e two s u b s e r i e s suggested t h a t t h e optimum compound f o r development should s t i l l contain the p - C l - a n i l i n e moiety, so that d i f l u b e n z u r o n was u l t i m a t e l y s e l e c t e d as the f i n a l benzoylphenyl urea derivative to be developed as a news e l e c t i v e insecticide.

Fate

o f diflubenzuron i n the

environment.

Soils (28, 2 £ ) . L e t us f i r s t discuss the rate of degradation o f diflubenzuron i n a g r i c u l t u r a l s o i l s . T h e h a l f l i f e f o u n d i n i t i a l l y w a s 8 - 16 w e e k s ,

13.

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Benzoylphenyl

AND FERRELL

247

Ureas

depending on the type o f s o i l ( T a b l e l ) . T h i s was s t i l l rather high i n comparison with the h a l f l i f e of 2 - 3 weeks f o u n d f o r t h e model compound 2,6difluorobenzamide. Further studies revealed the probable explanation o f this discrepancy. I t was f o u n d t h a t t h e h a l f l i f e o f d i f l u b e n z u r o n was l a r g e l y dependent o n t h e form i n w h i c h i t was b r o u g h t into the s o i l , as i s i l l u s t r a t e d i n Table 1.

Table 1. I n f l u e n c e o f p a r t i c l e size on apparent o f d e g r a d a t i o n o f d i f l u b e n z u r o n ( 2 8 , , 22.) ·

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch013

rate T-g-

i n weeks

PH

60-38

25

-

50

8-25

i n several

soils

Formulation

Diflubenzuron

8

-

16

0.5-1

S u s p e n s i o n , mean particle s i z e ^ΙΟρι. Suspension, particle

-

Approx.1

Aqueous

_ Pestic.

suspension •

mean

size

2^u

solution

_ >pestic . solution

J> m e t a b o l i t e s

In the i n i t i a l experiments particles with an average s i z e o f '\0ja h a d b e e n u s e d , b u t a h a l f l i f e o f 0.5 1 week was f o u n d when p a r t i c l e s with an average size o f 2u w e r e a p p l i e d . T h i s i n t e r e s t i n g p h e n o m e n o n might be caused by the s p e c i f i c p h y s i c a l properties of d i f l u b e n z u r o n : owing to i t s v e r y l o w aqueous s o l u b i l i t y o f a b o u t 0.2 ppm t h i s i n s e c t i c i d e , like other p e s t i c i d e s with a low s o l u b i l i t y , w i l l be present i n the s o i l as a d i s p e r s i o n i n the concen­ t r a t i o n a p p l i e d . Thus i n the equation given i n Table one t h e a p p a r e n t h a l f l i f e may b e g o v e r n e d b y t h e r a t e o f d i s s o l u t i o n , k-| , o r b y t h e t r u e r a t e o f degradation, k2· On u s i n g p a r t i c l e s with an average s i z e o f 2u, k2 i s a p p a r e n t l y r a t e d e t e r m i n g because i n t h a t c a s e t h e h a l f l i f e o f 0.5 1 week i s s i m i l a r to t h a t f o u n d when a t r u e s o l u t i o n i s a p p l i e d . T h e rate of dissolution of particles i s generally cor­ related l i n e a r l y with their surface

American Chemical Society Library 1155 16th St. N. W. Washington, D. C. 20038

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch013

248

PESTICIDE C H E M I S T R Y IN T H E 2 0 T H

CENTURY

a r e a , so t h a t k-j w i l l d e c r e a s e i f l a r g e r p a r t i c l e s are a p p l i e d . With c r y s t a l s l i k e those of d i f l u b e n z u r o n - h a v i n g a h i g h m e l t i n g p o i n t and consequently a h i g h energy of c r y s t a l l i s a t i o n - the r a t e of d i s s o l u t i o n o f l a r g e r p a r t i c l e s m i g h t b e so l o w t h a t k-j b e c o m e s r a t e d e t e r m i n i n g , i . e. k j < ^-2* W i t h t h e r e l a t e d c o m p o u n d PH 6 0 - 3 8 , ( I I I ) , a comparable but s m a l l e r e f f e c t of the p a r t i c l e size on t h e a p p a r e n t r a t e o f d e g r a d a t i o n i n s o i l s was o b s e r v e d a s i s i l l u s t r a t e d i n T a b l e 1. T h e influence o f t h e t y p e o f s o i l on t h e r a t e o f d e g r a d a t i o n o f d i f l u b e n z u r o n i s much l e s s i m p o r t a n t , b e c a u s e w i t h f i v e a g r i c u l t u r a l s o i l s and t h r e e h y d r o s o i l s , i n c l u d i n g t h e s o i l t y p e s recommended b y t h e EPA and t h e G e r m a n BBA, the v a r i a t i o n i n the h a l f l i f e was only a factor of approximately two. The r a t e o f d e g r a d a t i o n o f d i f l u b e n z u r o n i n a t e r r e s t r i a l s o i l was a l s o s t u d i e d b y M e t c a l f e t a l . (30), who f o u n d p r a c t i c a l l y no d e g r a d a t i o n k w e e k s a f t e r a p p l i c a t i o n o f an a c e t o n i c s o l u t i o n o f d i f l u b e n z u r o n t o a i r - d r i e d s o i l . We, however, o b s e r ­ ved that d i f l u b e n z u r o n c r y s t a l l i z e d from a c e t o n i c s o l u t i o n "on" s o i l w i t h a p a r t i c l e s i z e o f l a r g e l y >10 /u. T h e c o m m e r c i a l WP f o r m u l a t i o n o f d i f l u b e n z u r o n has a s t a n d a r d i z e d p a r t i c l e s i z e o f 1 - 5 ρ w i t h an a v e r a g e v a l u e o f 2 yU, so t h a t t h e s e h i g h e r h a l f l i f e v a l u e s o b t a i n e d w i t h l a r g e r p a r t i c l e s a r e o f no practical significance. This standardisation of the p a r t i c l e s i z e i s a l s o n e c e s s a r y because of i t s g r e a t i n f l u e n c e on t h e i n s e c t i c i d a l a c t i v i t y o f b e n z o y l p h e n y l u r e a s . T h i s was a l r e a d y m e n t i o n e d i n t h e d i s c u s s i o n o f t h e QSAR s t u d i e s . T h e influence o f p a r t i c l e s i z e on t h e l a r v i c i d a l a c t i v i t y o f d i f l u b e n z u r o n was f u r t h e r i l l u s t r a t e d e l s e w h e r e · T h e s e i n f l u e n c e s m i g h t h a v e t h e same e x p l a n a t i o n as t h a t o f t h e e f f e c t o f p a r t i c l e s i z e on t h e r a t e of degradation i n s o i l s . More d e t a i l e d s t u d i e s o f t h e m e t a b o l i c pathways o f d i f l u b e n z u r o n i n s o i l s have been c a r r i e d out w i t h radioactive preparations labeled i n four different p o s i t i o n s of the molecule f o r a study of the u l t i ­ mate f a t e o f t h e p r i m a r y d e g r a d a t i o n p r o d u c t s . T h e s e s t u d i e s w i l l be m e r e l y summarized i n t h i s p a p e r . A more e x t e n s i v e d i s c u s s i o n i s p u b ­ l i s h e d elsewhere (22.). I n a l l e x p e r i m e n t s d i s c u s s e d h e r e , d i f l u b e n z u r o n was a p p l i e d t o t h e s o i l a s a n a q u e o u s s u s p e n s i o n o f 2-yu p a r t i c l e s a t a c o n c e n ­ t r a t i o n o f 1 pg/gram s o i l , r o u g h l y c o r r e s p o n d i n g to a d o s e o f 300 grams a . i . p e r h e c t a r e . The first

13.

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AND

FERRELL

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249

Ureas

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch013

a s p e c t s t u d i e d was t h e n a t u r e of the primary degra­ dation process of d i f l u b e n z u r o n , by comparing the d e g r a d a t i o n i n normal s o i l s and i n steam-sterilized s o i l s . A representative example of the r e s u l t s with a preparation labeled with i n the a n i l i n e ring and w i t h a sandy loam s o i l i s i l l u s t r a t e d i n T a b l e 2. It can be seen t h a t i n the n o n s t e r i l e s o i l o n l y 2°/o o f d i f l u b e n z u r o n was l e f t a f t e r f o u r w e e k s . B u t i n the s t e r i l e soil s o m e 9k°/o o f t h e a p p l i e d d i f l u b e n z u r o n was s t i l l p r e s e n t after this p e r i o d . It can be c o n c l u d e d t h a t the d e g r a d a t i o n i s o f a m i c r o ­ biological nature.

T a b l e 2. Fate of d i f l u b e n z u r o n - r i n g - U - C i n sterile and n o n - s t e r i l e sandy loam s o i l a f t e r 4 weeks (Percentage of i n i t i a l amount o f d i f l u b e n z u r o n ) (28, 22) Sterile

Extractable

Extractable

C

PH 6θ-4θ

Nonsterile

96

43

9k

2

4

27

14 Non-extractable

C

A general survey of the m e t a b o l i c pathways of d i f l u b e n z u r o n i n s o i l s i s g i v e n i n F i g u r e 4. It was a l r e a d y mentioned that the main primary degradation process was a m i c r o b i o l o g i c a l h y d r o l y s i s o f the " b r i d g e " o f t h e m o l e c u l e i n s u c h a way ( r o u t e A) that j p - c h l o r o p h e n y l u r e a and 2,6-difluorobenzoic a c i d were f o r m e d . Let us f i r s t d i s c u s s the "urea" part of the d i f l u b e n z u r o n m o l e c u l e . p - C h l o r o p h e n y l u r e a was i d e n t i f i e d b y t h i n - l a y e r chromatography (tic), reversed isotope dilution analysis (rid), and mass s p e c t r o m e t r y (ms). U p t o 10°/o o f t h e l4c-aniline l a b e l a p p l i e d t o t h e s o i l was r e c o v e r e d as p-chlorophenyl urea, d e p e n d i n g on the type of s o i l , ~ w h i c h clearly illustrates that t h i s pathway i s of primary importance. The r a t e of the d e g r a d a t i o n processes i s i l l u s t r a t e d i n t h e u p p e r h a l f o f F i g u r e 5> with r e s p e c t to an a g r i c u l t u r a l sandy loam s o i l . It can b e s e e n t h a t b e t w e e n 2 a n d 28 w e e k s t h e a m o u n t of extractable radioactivity is practically identical w i t h the amount o f p - c h l o r o p h e n y l u r e a found.

PESTICIDE

250

co +

CENTURY

C-,F-deriv

H0 2

2

(phys.-chem., ring 3 ) H

(chem.,14c)

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch013

C H E M I S T R Y IN T H E 2 0 T H

^~^CONH

COOH

2

(riXtlc.)

(rid,ms,tlc.)

4 N-i-C-i-N-fVci H

H

C0

2

(rid,ms,tlc.)

(Hydrolysis, Chem.) Figure 4. Proposed pathways of the degradation of diflubenzuron in agricultural soils and hydrosoils. Abbreviations: rid = reversed isotope-dilution; ms = mass spectrometry; tic = thin layer chromatography.

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch013

13.

VERLOOP

AND FERRELL

Benzoylphenyl

Ureas

251

The f a t e o f t h i s p r i m a r y m e t a b o l i t e i s f u r t h e r i l l u s t r a t e d i n t h e lower h a l f o f F i g u r e 5 where the degradation o f p - c h l o r o p h e n y l urea i s g i v e n when t h i s ^ C - a n i l i n e r i n g - l a b e l e d compound was a p p l i e d t o t h e same t y p e o f s o i l i n a s e p a r a t e experiment. I n both studies a h a l f l i f e o f about 10 w e e k s w a s f o u n d f o r t h i s m e t a b o l i t e . The decrease of p-chlorophenyl urea can rather quantitatively be e x p l a i n e d b y t h e g r a d u a l f o r m a t i o n o f bound r e s i d u e s . We a r e c u r r e n t l y s t u d y i n g t h e n a t u r e o f the bound r e s i d u e s , f o r i n s t a n c e b y means o f e x traction procedures which avoid the formation of a r t e f a c t s . T h i s method has r e v e a l e d that t h e bound residues c o n t a i n j3-chlorophenyl urea as w e l l as s m a l l amounts o f p - c h l o r o a n i l i n e · Free p-chloroa n i l i n e o r i t s f u r t h e r p o s s i b l e d e g r a d a t i o n productsy e.g. c h l o r i n a t e d a z o - and azoxybenzenesywere not present i n the extractable residues. The main d e g r a d a t i o n pathway o f d i f l u b e n z u r o n i n s o i l s would lead to the formation also o f 2,6d i f l u o r o b e n z o i c a c i d as a primary m e t a b o l i t e . Starting with diflubenzuron preparations labeled w i t h I ^ C a n d -^H i n t h e b e n z o y l r i n g , 2,6-dif luorobenzoic a c i d has indeed been i d e n t i f i e d b y t h i n layer chromatography (tic), gas chromatography (glc), reversed isotope dilution analysis (rid), a n d mass spectrometry (ms). Because o f i t s r a p i d further degradation i n agricultural soils with a h a l f l i f e of less than k weeks, t h e maximum amount o f 2,6d i f l u o r o b e n z o i c a c i d f o u n d w a s 20^ of the diflubenz u r o n a p p l i e d . T h e f a t e o f t h e a c i d was s t u d i e d further with a diflubenzuron preparation labeled with i n the carbonyl group o f the benzoyl moiety. The major part of this labeled material was i d e n t i f i e d b y c h e m i c a l a n a l y s i s a f t e r about 12 weeks as C0£, p r o v i n g t h a t d e c a r b o x y l a t i o n i s t h e f i r s t step i n the degradation o f 2,6-difluorobenzoic acid. F u r t h e r i n f o r m a t i o n was o b t a i n e d w i t h d i f l u b e n zuron l a b e l e d w i t h 3H i n t h e b e n z o y l r i n g . In this study, u p t o 50°/o o f t h e t r i t i u m l a b e l a d d e d t o a c l a y h y d r o - s o i l was i d e n t i f i e d as t r i t i a t e d water. As m e n t i o n e d e a r l i e r , hydrolysis according to route 2 or 3 leading to p - c h l o r o a n i l i n e and 2,6d i f l u o r o b e n z a m i d e i s t h e ' m a i n pathway i n t h e slow degradation of the "sister" c o m p o u n d P H 60-38. As e x p e c t e d t h i s pathway was d e m o n s t r a t e d a l s o i n the case o f d i f l u b e n z u r o n , though as a minor process: 2,6-difluorobenzamide has been identified i n a m o u n t s o f a t t h e m o s t 2°/o o f t h e a p p l i e d d o s e b y means o f t h i n l a y e r c h r o m a t o g r a p h y ( t i c ) and rever-

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch013

1004

Figure 5. Rate of degradation of diflubenzuron (upper half) and of p-chlorophenyl urea (lower half) in an agricultural sandy loam soil Percent recovery of applied dose.

13.

VERLOOP

AND

FERRELL

Benzoylphenyl

253

Ureas

sed isotope d i l u t i o n a n a l y s i s (rid). In separate experiments w i t h 3 H - d i f l u o r o b e n z a m i d e i t was found to be d e g r a d e d r a p i d l y i n t o 2,6-difluorobenzoic a c i d w i t h a h a l f l i f e o f a b o u t two w e e k s i n a clay hydrosoil ( F i g u r e 6). In this experiment the h a l f l i f e o f t h e 2 , 6 - d i f l u o r o b e n z o i c a c i d f o r m e d was a g a i n about k weeks ( 2^.) ·

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch013

Plants. I n c o n t r a s t to the degradation of diflubenzuron i n the i n s e c t i c i d e i n p l a n t s a f t e r rather simple. Table leaves two greenhouse

fast and complicated soils, the f a t e of leaf application is

3· Persistence of d i f l u b e n z u r o n on p l a n t months a f t e r t o p i c a l a p p l i c a t i o n i n a s t u d y (^J.) · percentage

of

applied

dose

maize

cabbage

100

Fraction soybean

apple

TER

93

86

9k

Diflubenzuron

96

89

95

k

TBR

97

TR

TER TBR TR

= Total = Total = Total

2 88

5 99

100

5

105

extractable residue. bound r e s i d u e . residue.

T h i s i s i l l u s t r a t e d i n T a b l e 3> where an analysis is presented of plant leaves two m o n t h s a f t e r app l i c a t i o n o f l a b e l e d d i f l u b e n z u r o n as an aqueous suspension of 2 u particles on soybean, apple, maize and cabbage p l a n t s i n a greenhouse study. It can be

254

PESTICIDE

C H E M I S T R Y IN T H E 2 0 T H C E N T U R Y

RECov£Ry

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch013

%I

Figure 6. Degradation curves of 2,6-difluorobenzamide and 2,6-difluorobenzoic acid after incubation of clay hydrosoil with Η-2,6-difluorobenzamide. Recovery in percen­ tage of applied dose. 3

13.

VERLOOP

AND FERRELL

Benzoylphenyl

255

Ureas

observed that ^ 95°/o o f t h e a n a l y s e d radioactivity was f o u n d i n t h e e x t r a c t a b l e f r a c t i o n a n d t h a t i t consisted completely of unaltered diflubenzuron. At h a r v e s t , 4 - 5 months a f t e r a p p l i c a t i o n , t h e c r o p s were a n a l y z e d ( T a b l e 4).

T a b l e 4. R e s i d u e s i n c r o p s , 4 - 5 months after leaf application of ^H-1^C-iabeled diflubenzu­ ron (calculated a s ppmd i f l u b e n z u r o n ) (31)

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch013

Total

3

H

Total

λ

^0

Soybean,

milled

beans

< 0.02

<

0.02

Maize,

milled

grains

< 0.001

<

0.001

< 0.002

<

0.005

Apples

Labels :

From t h e r e s u l t s i t i s clear that no r e s i d u e s were found up to the s e n s i t i v i t y l i m i t of the analytical methods u s e d . Furthermore u n t r e a t e d leaves were found to c o n t a i n p r a c t i c a l l y no r a d i o a c t i v e material. It can be concluded that d i f l u b e n z u r o n a f t e r appli­ cation on plants i s very persistent a n d h a s no sys­ temic p r o p e r t i e s . In other s t u d i e s i t was f o u n d that d i f l u b e n z u r o n does n o t permeate through the cuticular barrier into the leaves o f broad bean. These studies on the fate of diflubenzuron on and i n plants w i l l be p u b l i s h e d more e x t e n s i v e l y elsewhere (,2J.) . E s s e n ­ t i a l l y t h e same r e s u l t s were o b t a i n e d b y S t i l l i n a study on the metabolic fate o f diflubenzuron on cotton plants (32). I n a d d i t i o n to metabolism, other f a c t o r s might i n f l u e n c e the fate o f d i f l u b e n z u r o n on p l a n t s , i . e . washing o f f and photochemical deg­ radation. R u z o e t a l . (33) a n d M e t c a l f e t a l . (30) studied the photodegradation of diflubenzuron at respectively >285 n m a n d 2 5 ^ n m , f o r e x a m p l e i n methanol, under rather drastic conditions and found e s s e n t i a l l y t h e same d e g r a d a t i o n pathways.

PESTICIDE C H E M I S T R Y IN T H E 2 0 T H C E N T U R Y

256

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch013

However, u n d e r more n a t u r a l c o n d i t i o n s , e . g . accor­ d i n g to t h e methods recommended i n t h e EPA G u i d e ­ l i n e s t h e r a t e o f t h e p h o t o c h e m i c a l d e g r a d a t i o n was f o u n d t o b e v e r y l o w (3^ ) · I n o t h e r experiments washing o f f o f diflubenzuron from plant leaves with h i g h amounts o f s i m u l a t e d r a i n f a l l was f o u n d t o b e negligible {^h.) · A l l t h e s e r e s u l t s point to a high residual activity of diflubenzuron after application to t h e crops a n d to t h e absence o f any metabolites formed by d i r e c t degradation on or i n the plants. Insects and ecosystems. A high s t a b i l i t y of d i f l u b e n z u r o n was a l s o f o u n d a f t e r u p t a k e b y i n s e c t s . I n T a b l e 5 some s t u d i e s a r e s u m m a r i z e d o f t h e f a t e of diflubenzuron and the parent c o m p o u n d D u 19111· Table

5»

Fate

of benzoylphenyl ureas Clearance

a)

i n

insects.

Insect

Application

Absorption

P.brassicae larvae (36)

Suspension on leaves

0.5

30-35

A.

Topical

1-2

100

-

25-40

b

Diflubenzuron

+/0

grandis (2Z)

E. acrea larvae (30)

and

injection Suspension i n medium pu_19111

Ρ . b r a s s i c a e larvae (35)

Suspension on leaves

a)

b)

Tj- i n days;

Percentage

1

of applied

>

35

dose.

I n a l l c a s e s , m e t a b o l i s m was f o u n d t o b e c o m p l e t e l y absent. T h e amount o f a b s o r p t i o n b y t h e i n s e c t s depends on t h e method o f a p p l i c a t i o n ; especially a f t e r oral uptake of suspensions, a b o u t 2/3 o f t h e labeled material remains i n the gut and i s excreted i n the faeces. However, the absorbed m a t e r i a l i s also readily excreted: f o r the clearance an average T-g- o f a b o u t o n e d a y w a s f o u n d . T h i s phenomenon explains the reversible character of the i n s e c t i c i d a l a c t i v i t y of diflubenzuron. The high s t a b i l i t y i n

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch013

13.

VERLOOP

A N D FERRELL

Benzoylphenyl

Ureas

257

i n s e c t s was a l s o a p p a r e n t i n a s t u d y o f the b e h a v i o u r o f d i f l u b e n z u r o n i n the M e t c a l f model ecosystem (30)* Some o f the r e s u l t s o b t a i n e d a r e p r e s e n t e d i n T a b l e 6. The s o - c a l l e d e c o l o g i c a l m a g n i f i c a t i o n , d e f i n e d i n T a b l e 6, was d e t e r m i n e d f o r t h r e e d i f f e r e n t r a d i o ­ l a b e l e d p r e p a r a t i o n s A, B, and C. I t can be seen t h a t mosquito l a r v a e , w h i c h a r e i n the m i d d l e o f the M e t c a l f f o o d c h a i n , show a r a t h e r h i g h m a g n i f i c a t i o n . But the m a g n i f i c a t i o n found i n f i s h was more t h a n an o r d e r o f magnitude l o w e r , so t h a t the a u t h o r s c o n ­ c l u d e d t h a t d i f l u b e n z u r o n d i d not b i o c o n c e n t r a t e i n the f i s h t h r o u g h f o o d - c h a i n t r a n s f e r . The m a g n i f i c a ­ t i o n found i n s n a i l s i s a l s o r e a s s u r i n g e s p e c i a l l y i n c o m p a r i s o n w i t h the c o n c e n t r a t i o n s found i n a l g a e . I n r e s p e c t to DDT, M e t c a l f et a l . have r e p o r t e d e c o ­ l o g i c a l m a g n i f i c a t i o n s o f 10^000 f o r f i s h and o f 5000 f o r s n a i l i n t h e i r model e c o s y s t e m (38). T a b l e 6. B i o a c c u m u l a t i o n M e t c a l f model ecosystem (30) Biological

Object

of diflubenzuron i n

E c o l o g i c a l m a g n i f i c a t i o n (E.M.) with labeled preparation Β

Snail Fish

(Physa sp.) (Gambusa affinis)

Mosquito l a r v a e ( C u l e x sp.)

86

95

19

^k

779

221 80

596

1099

C=A Labels :

14 UE.M.

=

Concentration Concentration

in biological i n water

C=B

object

a f t e r 33 days

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch013

258

PESTICIDE C H E M I S T R Y IN T H E

20TH

CENTURY

Animals. F i n a l l y a n o t h e r i m p o r t a n t a s p e c t to be d i s c u s s e d , e.g. i n r e l a t i o n to mammalian t o x i c o l o g y , i s the f a t e o f d i f l u b e n z u r o n i n a n i m a l s . P o s t , W i l l e m s and co-workers have s t u d i e d the f a t e o f the i n s e c t i c i d e i n the r a t a f t e r o r a l a d m i n i s t r a t i o n o f 3 H - b e n z o y l and ^ C - a n i l i n o r i n g — l a b e l e d p r e p a r a t i o n s . C o n s i s t e n t r e c o v e r i e s o f r a d i o a c t i v i t y were o b t a i n e d i n a l l s t u d i e s , most o f i t b e i n g r e t r i e v e d i n u r i n e and f a e c e s . The r a d i o a c t i v i t y i n the c a r c a s s e s was o n l y a few p e r cent o f each l a b e l , so t h a t t h e r e i s no a c c u m u l a t i o n o f d i f l u b e n z u r o n o r m e t a b o l i t e s i n the r a t body. From the amounts o f l a b e l f o u n d i n the u r i n e and b i l e i t was c o n c l u d e d t h a t a t l e a s t 50°/o o f a dose was a b s o r b e d by the i n t e s t i n e s . The r e s o r b e d d i f l u b e n z u r o n was ( a l m o s t ) c o m p l e t e l y metab­ o l i z e d . The p r o p o s e d m e t a b o l i c pathways a r e g i v e n i n F i g u r e 7 . I t can be o b s e r v e d t h a t about 20°/o i s d e g r a d e d i n the same way as f o u n d i n the s o i l s t u d i e s , i . e . a h y d r o l y s i s o f the " b r i d g e " o f the m o l e c u l e l e a d i n g to 2 , 6 - d i f l u o r o b e n z o i c a c i d and p-chlorophenyl u r e a as p r i m a r y m e t a b o l i t e s . Most o f the p - c h l o r o ­ p h e n y l u r e a i s f u r t h e r d e g r a d e d , which was a l s o f o u n d i n s e p a r a t e s t u d i e s i n which ^ C - l a b e l e d - p - c h l o r o p h e n y l u r e a i t s e l f was a d m i n i s t e r e d o r a l l y to r a t s . I n the r a t s t u d i e s a major a d d i t i o n a l m e t a b o l i c pathway was d i s c o v e r e d , which had not been f o u n d i n s o i l s , i . e . the h y d r o x y l a t i o n o f the i n t a c t d i f l u b e n ­ z u r o n m o l e c u l e l e a d i n g to the t h r e e d i f f e r e n t m e t a b o l i t e s i n d i c a t e d i n the F i g u r e , which were f o u n d p a r t l y as c o n j u g a t e s . These h y d r o x y d e r i v a t i v e s a c c o u n ­ t e d f o r a l m o s t a l l the m e t a b o l i t e s i n the b i l e and f o r about h a l f the m e t a b o l i t e s i n the u r i n e . The r a t m e t a b o l i s m s t u d i e s w i l l be p u b l i s h e d more e x t e n s i v e l y e l s e w h e r e (22.) ·

Mode o f a c t i o n o f

diflubenzuron.

I n the i n t r o d u c t i o n i t was s t a t e d t h a t the d i s t u r b a n c e s o f the e n d o c u t i c u l a r m a t r i x o f P i e r i s b r a s s i c a e l a r v a e by the p a r e n t b e n z o y l p h e n y l urea compound Du 19111 were caused by an i n f l u e n c e on c h i t i n f o r m a t i o n , thus a s s i g n i n g to the benzoylphenyl u r e a s an i n s e c t i c i d a l p o s i t i o n e q u i v a l e n t to t h a t o f the f u n g i c i d a l p o l y o x i n s . I n the l a s t p a r t o f t h i s p a p e r we s h a l l t r y to adduce arguments s u p p o r t i n g t h a t statement. The f i r s t argument was s u p p l i e d by Post and V i n c e n t ( 4 θ ) i n t h e i r s t u d y o f the i n c o r p o r a t i o n o f r a d i o l a b e l e d glucose i n t i s s u e f r a c t i o n s o f normal

VERLOOP

AND

Benzoylphenyl

FERRELL

Ureas

Several

metabolites

18

COOH

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch013

•C- Ν Il

Ο

I

Η

C- Ν ό'

Η

t +

• V\

H „ N - C NΗ - ( 1

- C - Ν -C

W>CI

Va

\ C II

Ο

OH

C- Ν - C 6 H ô

HO

C - Ν - C - Ν -C

\ Cl

Il

I

II

I

/

Ο

H

Ο

H

\

\=/

Conjugates Figure 7.

Proposed metabolic pathway of diflubenzuron in rats (percentages of resorbed material)

PESTICIDE C H E M I S T R Y IN T H E 2 0 T H C E N T U R Y

260

and

D u 19111

treated

P i e r i s

brassicae

larvae

(Table

7)

^ T a b l e 7· Incorporation o f radioactivity from (6C)-D-glucose i n tissue fractions o f normal and Du 19111-treated P i e r i s l a r v a e , expressed a s jag glucose, with standard deviations (40). Haemolymph plus gut contents

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch013

Control

Treated

Ο.69

+0.21 Ο.96

+0.25

KOH h y d r o l - G l y c o g e n ysate and fraction washings (pellets)

1.74

+0.34 2.48

+0.51

Ο.38

+0.11 0.59

+0.16

Chitin Total fraction (cuti­ cles) 1.25

+0.34 0.02

+0.01

4.03

+0.54 4.05

+0.59

From t h i s T a b l e i t i s c l e a r , on the one hand, the total r a d i o a c t i v i t i e s incorporated i n the tissues o f normal andtreated larvae a r e i d e n t i c a l . On t h e o t h e r hand, however, p r a c t i c a l l y no l a b e l e d glucose has been incorporated i n the c h i t i n f r a c t i o n from the cuticles. Theother tissue fractions show a s l i g h t l y increased amount o f r a d i o a c t i v i t y . The l o c a l i s a t i o n of the i n h i b i t i o n o f glucose i n c o r p o r a t i o n was s t u d i e d f u r t h e r b y Post a n d c o - w o r k e r s b y means o f m i c r o ­ autoradiography (4j_) . I t w a s f o u n d t h a t i n e n d o c u t i c l e of P i e r i s larvae a narrow zone o f r a d i o a c t i v i t y i s formed a f t e r i n j e c t i o n o f ( H - ) - D - g l u c o s e . By contrast, in the larvae t r e a t e d w i t h D u 19111 v i a l e a f feeding, this zone was c o m p l e t e l y a b s e n t . I n the incorporation study b y Post a n d V i n c e n t (40 ) , D u 19111 h a d b e e n a d m i n i s t e r e d b y f e e d i n g o f t r e a t e d cabbage leaves to f i f t h i n s t a r Pieris larvae d u r i n g 24 h o u r s prior to i n j e c t i o n o f l a b e l e d g l u c o s e , while the analysis w a s c a r r i e d o u t 24 h o u r s a f t e r i n j e c t i o n . T h i s study was r e p e a t e d with diflubenzuron by Deul et a l . (42) and e s s e n t i a l l y t h e same r e s u l t s were obtained. However, Deul et a l . also studied the rapidity of i n h i b i t i o n b y d i f l u b e n z u r o n : they i n j e c t e d Re­ labeled glucose into control larvae and ^ C - l a b e l e d glucose + diflubenzuron into test larvae and analysed the i n c o r p o r a t i o n as a f u n c t i o n o f time a f t e r i n j e c ­ tion (4_2) . T h e r e s u l t s a r e summarized i n Figure 8. It c a n b e c o n c l u d e d t h a t most o f t h e i n c o r p o r a t i o n in the controls hadalready taken place 15 m i n u t e s after i n j e c t i o n andthat diflubenzuron i s capable o f

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AND

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Ig cpm = incorporation of radioactivity from injected [6 - C ] - D -glucose. 1,2 ... hours = time after (simultaneous) injection of radioactive glucose. 14

• = controls. ο = treated with

1

larva

Figure 8. Rate of inhibition of chitin synthesis after injection of diflu­ benzuron in fifth instar Pieris brassicae larvae 24 hr after ecdysis

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i n h i b i t i n g t h i s i n c o r p o r a t i o n to the e x t e n t o f >95°/o even a f t e r such a s h o r t p e r i o d . I n d i c a t i o n s o f the r a p i d i t y o f a c t i o n o f d i f l u b e n z u r o n on the c h i t i n d e p o s i t i o n were a l s o o b t a i n e d by Ker (4^2.) i n h i s s t u d i e s o f the e f f e c t o f the i n s e c t i c i d e on a d u l t l o c u s t s . I n one s t u d y , a d u l t l o c u s t s were s t a r v e d p r i o r to b e i n g g i v e n d i f l u b e n z u r o n - t r e a t e d b a r l e y f o r s i x h o u r s , a f t e r which t h e y r e t u r n e d to u n t r e a t e d b a r l e y . I n m i c r o p h o t o g r a p h s o f the pre a l a r arm and o f the h i n d t i b i a o f l o c u s t s i n p o l a r i z e d l i g h t a band o f non-birefringent m a t e r i a l , i . e . free of c h i t i n , can be o b s e r v e d which c o r r e s p o n d s to not more t h a n a day's growth. I n a n o t h e r s t u d y d i f l u b e n z u r o n was i n j e c t e d and i t was found t h a t the p r o d u c t i o n o f c h i t i n l e s s c u t i c l e s t a r t e d i n l e s s t h a n 80 minutes

On). From the r e s u l t s d i s c u s s e d so f a r i t can be concluded that diflubenzuron i n t e r f e r e s very r a p i d l y w i t h c h i t i n d e p o s i t i o n . The p o s s i b l e e f f e c t s on the d e p o s i t i o n o f p r o t e i n , the second i m p o r t a n t component o f the e n d o c u t i c u l a r m a t r i x , were s t u d i e d by H u n t e r and V i n c e n t w i t h a d u l t l o c u s t s (h^) . I t was c o n c l u d e d t h a t p r o t e i n d e p o s i t i o n was c o m p l e t e l y u n a f f e c t e d as r e g a r d s the q u a n t i t y o f p r o t e i n f o u n d . A n o t h e r conc l u s i o n was t h a t c r o s s - l i n k i n g o f the p r o t e i n - as r e v e a l e d by the d i f f e r i n g s o l u b i l i t i e s o f the p r o t e i n f r a c t i o n s - was a l s o u n a f f e c t e d . D e u l et a l . (4 5) f u r t h e r m o r e f o u n d p r a c t i c a l l y no e f f e c t o f d i f l u b e n z u r o n on p r o t e i n s y n t h e s i s i n c u t i c l e s o f P i e r i s brassicae larvae. The mode o f a c t i o n o f d i f l u b e n z u r o n i n h o u s e f l y l a r v a e (Musca d o m e s t i c a ) was s t u d i e d by I s h a a y a and C a s i d a ( k 6 ) « These a u t h o r s found t h a t d i e t a r y d i f l u b e n z u r o n i n c r e a s e d the c u t i c l e c h i t i n a s e and p h e n o l o x i d a s e a c t i v i t i e s when a n a l y z e d t h r e e days a f t e r a d d i t i o n o f two-day o l d l a r v a e to the media. These a u t h o r s c o n s i d e r e d t h a t the i n c r e a s e d c h i t i n a s e l e v e l , p o s s i b l y caused by hormone s t i m u l a t i o n , might e x p l a i n the o b s e r v e d d e c r e a s e d c h i t i n d e p o s i t i o n . However, the complete i n h i b i t i o n o f g l u c o s e i n c o r p o r a t i o n w i t h i n 15 m i n u t e s i n P i e r i s b r a s s i c a e e n d o c u t i c l e might not e a s i l y be e x p l a i n e d by the c h i t i n a s e t h e o r y . F o r t h a t r e a s o n D e u l et a l . (^2.) c a r r i e d out a c o m p a r a t i v e s t u d y w i t h P i e r i s l a r v a e o f the i n f l u e n c e o f d i f l u b e n z u r o n on the i n h i b i t i o n o f g l u c o s e i n c o r p o r a t i o n , on the one hand, and on i t s i n f l u e n c e on the c h i t i n a s e a c t i v i t y , on the o t h e r . The r e s u l t s are p r e s e n t e d i n F i g u r e 9· I t can be o b s e r v e d t h a t one and t h r e e days a f t e r e c d y s i s , when g l u c o s e i n h i b i t i o n i s almost comp l e t e l y blocked, c h i t i n a s e a c t i v i t y i s p r a c t i c a l l y

13.

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51

lg cpm = Ig incorporation of radio activity from injected[6- *C]-D-glucose ν = chitinase activity in μηιοΐββ AGA/hr/grams larvae 1

• = controls ο = injected with 1 μg dif lubenzuron/larva Figure 9.

Influence of diflubenzuron on chitin synthesis and braeakdown instar Pieris brassicae larvae as a function of age after ecdysis

in fifth

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PESTICIDE C H E M I S T R Y I N T H E 2 0 T H C E N T U R Y

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch013

zero both i n treated and control larvae. After three days c h i t i n a s e a c t i v i t y starts to increase both i n treated and i n untreated larvae u n t i l the next moult about 6 days a f t e r e c d y s i s . The results of this experiment d e f i n i t e l y exclude the chitinase hypothesis t o e x p l a i n t h e p r i m a r y mode o f a c t i o n o f d i f l u benzuron, at least i n P i e r i s brassicae.

glucose

>glucose

N-acetyl

glucosamine

1

6-P

6-P^

N-acetylglucosamine

I

UDP-N-acetylglucosamine Figure 10.

^ fructose

1

6-P

glucosamine

6-P

1-P

^ c h i t i n

Biosynthetic pathway of chitin synthesis from glucose

The a l t e r n a t i v e p o s s i b i l i t y t o e x p l a i n t h e mode o f a c t i o n i s t h e i n h i b i t i o n o f one o f t h e enzymes i n the pathway o f c h i t i n b i o s y n t h e s i s , i l l u s t r a t e d i n Figure 10. C o n s i d e r i n g t h e r a p i d i t y o f t h e p r o c e s s , a direct i n h i b i t i o n w i t h o u t h o r m o n a l i n t e r f e r e n c e was most p r o b a b l e . Post et a l . compared the r a t e s o f incorporation o f ^C-labeled glucose into the u l t i mate c h i t i n p r e c u r s o r , uridine diphosphate N-acetylg l u c o s a m i n e o r UDPAG, i n b o t h n o r m a l a n d D u 19111treated P i e r i s larvae and found that these rates d i d not d i f f e r s i g n i f i c a n t l y · Hence the c o n c l u s i o n 1

seemed j u s t i f i e d t h a t t h e " p a r e n t " c o m p o u n d D u 19111 did not inhibit an intermediate step between glucose and UDPAG. T h i s l e d t o t h e h y p o t h e s i s t h a t either the u l t i m a t e enzyme o f t h e pathway, c h i t i n synthetase, was b l o c k e d o r t h a t a c l o s e l y r e l a t e d p r o c e s s w a s a f f e c t e d b y D u 19111. D e u l e t a l . f o u n d i n a n o t h e r study that diflubenzuron inhibited the incorporation of ^ C - l a b e l e d UDPAG i n t h e c h i t i n f r a c t i o n o f P i e r i s brassica cuticles a n d t h u s t h e y a r r i v e d a t t h e same conclusion with respect t o t h a t c o m p o u n d 0^2) . O f course the ultimate proof that diflubenzuron blocks c h i t i n synthetase i n Pieris brassicae larvae can only be o b t a i n e d b y i n h i b i t i o n e x p e r i m e n t s with the pure i s o l a t e d enzyme. But the i s o l a t i o n o f c h i t i n synthetase from insects i s a notoriously d i f f i c u l t problem 1

13.

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265

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch013

and our e f f o r t s i n t h a t a r e a have n o t as y e t l e d to success· In this context the comparison of the i n s e c t i ­ c i d e d i f l u b e n z u r o n w i t h the f u n g i c i d e p o l y o x i n D i s interesting i n more t h a n one r e s p e c t . It not only c l o s e s the c i r c l e i n our paper, so t o speak, but i t can also furnish strong circumstantial evidence to support our hypothesis o f t h e mode o f a c t i o n of diflubenzuron. M a r k s a n d Sowa w e r e t h e f i r s t to com­ pare d i f l u b e n z u r o n and p o l y o x i n D i n t h e i r effects on the ^ - e c d y s o n - d e p e n d e n t i n - v i t r o synthesis of c h i t i n by the cockroach (Leucophaea maderae) leg regenerates . These authors found that both compounds almost completely i n h i b i t e d the incorpora­ tion of ^ C - l a b e l e d D-glucosamine i n t o the c h i t i n fraction. In a later study with ^C-labeled N-acetylD-glucosamine similar results were o b t a i n e d , and the I50 v a l u e o f i n h i b i t i o n o f c h i t i n s y n t h e s i s was f o u n d t o b e 6.11 χ 10 -10M f o r d i f l u b e n z u r o n and 7.53 x 10-7 M f o r p o l y o x i n D (kS). The difference in i n t r i n s i c a c t i v i t y can p a r t l y be e x p l a i n e d by the roughly hundredfold accumulation of d i f lubenzuron i n the i n s e c t tissue. 1

These i n t e r e s t i n g r e s u l t s prompted us to compare d i f l u b e n z u r o n and p o l y o x i n D i n t h e i r effects on Pieris brassicae larvae (^£,2.) · I n p r e l i m i n a r y s t u d i e s i t had been found that p o l y o x i n D d i d not affect the larvae v i a leaf feeding but that i n j e c t i o n re­ sulted i n l a r v i c i d a l effects. H i s t o l o g i c a l examina­ tion revealed t h a t b o t h compounds gave similar effects, i . e . the d i s t u r b a n c e of the r e g u l a r endocuticular layers and the formation of globular coagulated particles as d i s c u s s e d e a r l i e r f o r Du 19111. F u r t h e r i n f o r m a t i o n w a s o b t a i n e d b y i n c o r p o r a ­ tion studies a s i s i l l u s t r a t e d i n T a b l e 8. After leaf f e e d i n g o f p o l y o x i n D no e f f e c t on the incorpo­ ration of radiolabeled glucose c o u l d be observed, even at a tenfold higher dose. But q u i t e comparable e f f e c t s were o b t a i n e d w i t h the two c o m p o u n d s after incubation with a preliminary " i n v i t r o " system. After injection, when p a r t of the permeability barriers i n the larvae is absent, polyoxin D i n h i b i t s the glucose incorporation, but less so t h a n diflubenz u r o n . The c o n c l u s i o n seems o b v i o u s t h a t the i n t r i n ­ sic e f f e c t s o f b o t h compounds are p r a c t i c a l l y iden­ t i c a l b u t t h a t p o l y o x i n D i s much more h i n d e r e d by the p e r m e a b i l i t y b a r r i e r s present i n the Pieris brassicae larvae. On t h e s t r e n g t h of the evidence presented by Misato and co-workers that polyoxin D is a competitive i n h i b i t o r of c h i t i n synthetase, a

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similar zuron

conclusion

seems

for

j u s t i f i e d

the

mode

of

action

of

difluben-

( 49 )

14 T a b l e 8. I n h i b i t i o n of incorporation -D-glucose into c h i t i n fractions of P i e r i s larvae by d i f l u b e n z u r o n and p o l y o x i n D , as of controls.

o f (6C) brassicae percentage

Diflubenzuron

Polyoxin

D

Dose (nmoles)

Dose Inhibi(nmoles ) t i o n ( ^ )

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Method

Oral uptake larvae v i a feeding

by leaf

10-20

Inhibit i o n (°/o)

95

200

Ο

Injection into larvae,simultaneous with glucose

3

90

50

45

Injection into larvae, 3 hours p r i o r to glucose

-

-

50

95

Incubation with skin + adhering tissue

30

80

80

80

In a d d i t i o n to the e f f e c t s of d i f l u b e n z u r o n on the chitinase and phenoloxidase l e v e l s , observed by Ishaaya a n d C a s i d a (46 ) , o t h e r b i o c h e m i c a l influences o f d i f l u b e n z u r o n a n d D u 19111 have been d e s c r i b e d i n the l i t e r a t u r e ( T a b l e 9). A common f e a t u r e of a l l t h e s e e f f e c t s i s t h e i r a n a l y s i s one o r more days a f t e r t r e a t m e n t . As any e f f e c t s of these b e n z o y l p h e n y l u r e a s become v i s i b l e on the l i v i n g insects o n l y at the time o f the n e x t m o u l t , when susceptible larvae die, investigators are prompted to search for defects up to a c o n s i d e r a b l e time a f t e r application. In comparison w i t h the v e r y f a s t i n h i b i t i o n of c h i t i n synthesis discussed above, i n our opinion these studies can at the most i n d i c a t e "secondary" effects. A c o n s i d e r a b l e number o f e f f e c t s of this t y p e can be expected to be f o u n d and p u b l i s h e d i n the future·

13.

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T a b l e 9 . "Secondary" e f f e c t s ureas i n i n s e c t s . Compound

Insect

(52)

Pieris b r a s s i c a e L. Thaumetopoae p i t y o campa S.

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch013

Du

19111

larvae

L.

D i f l u b e n z - Musc a u r o n ( 46 ) d o m e s t i c a

L.

D i f l u b e n z - Musca domestica uron (5l)

L.

Diflubenz- Pieris uron (42.) brassicae

L.

19111

of

benzoylphenyl

Analysis Effect (days after treatment) 1,2 3 » 12

2

Pieris brassicae

Du (ito)

267

Ureas

Increase followed by d e c r e a s e o f respiratory m e t a b o l i s m and of pentose-cycle. Slightly increased b i o s y n t h e s i s of non-chitinous materials* Increase of c h i t i n a s e and phenoloxidase activity. Increased a c t i v i t y o f ^£-ecdysonmetabolizing enzymes and i n crease of microsomal o x i d a s e activity· S l i g h t l y increased b i o s y n t h e s i s of nonchitinous material·

Summarizing, dif lubenzuron f e a t u r e s mentioned i n the i n t r o d u c t i o n o f t h i s p a p e r can be completed as f o l l o w s : The new i n s e c t i c i d e has f a v o u r a b l e e n v i r o n m e n t a l p r o p e r t i e s because i t i s n o n - p e r s i s t e n t i n s o i l s and i t has a low b i o l o g i c a l m a g n i f i c a t i o n . I t i s s t a b l e on p l a n t s and i n i n s e c t s , hence i t has a l o n g r e s i d u a l a c t i v i t y . I t r e p r e s e n t s the b e s t c h o i c e from the s e r i e s o f the b e n z o y l p h e n y l u r e a s . I t i s a r e v e r s i b l e i n h i b i t o r of c h i t i n synthesis i n i n s e c t s , p r o b a b l y by b l o c k i n g c h i t i n synthetase.

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Abstract. The development of s e l e c t i v e crop p r o t e c t i o n compounds based on the i n t e r f e r e n c e with c h i t i n d e p o s i t i o n i n fungi and i n s e c t s i s one of the aims in p e s t i c i d e d e s i g n . P o l y o x i n D and kitazin have been s u c c e s s f u l l y developed along these l i n e s i n the field of f u n g i c i d e s some years ago. The benzoylphenyl ureas, which e x h i b i t a c t i v i t y against the l a r v a l sta­ ges of s e v e r a l i n s e c t species by i n t e r f e r i n g with chitin d e p o s i t i o n i n the endocuticle and thus with the moulting process, were first introduced i n 1 9 7 2 . The study of t h i s new s e r i e s u l t i m a t e l y l e d to the development of 1 - ( 4 - c h l o r o p h e n y l ) - 3 - ( 2 , 6 - d i f l u o r o ­ benzoyl) urea (common name diflubenzuron) as a new s e l e c t i v e l a r v i c i d e with favourable environmental p r o p e r t i e s . In the present paper t h i s development has been d i s c u s s e d , based on the l i t e r a t u r e as w e l l as on new r e s u l t s from our l a b o r a t o r i e s , with main emphasis on: 1) The o p t i m i s a t i o n of the s e r i e s by chemical synthesis guided by the study of quantita­ tive s t r u c t u r e - a c t i v i t y r e l a t i o n s h i p s ; 2) The ratio­ nal development of the s o i l degradable d i f l u b e n z u r o n from its more p e r s i s t e n t predecessors and its metab­ olic pathways i n soil, p l a n t s , animals and model ecosystems. 3) The mode of a c t i o n of d i f l u b e n z u r o n at the h i s t o l o g i c a l and molecular b i o l o g i c a l l e v e l . Literature 1. 2. 3. 4. 5· 6. 7. 8. 9.

cited

Endo, Α . , K a k i k i , Κ . , and Misato, T., J . B a c t e r i ol. (1970), 104, 189 and preceding papers. Maeda, T., Abe, Η . , K a k i k i , Κ . , and Misato, T., Agr. B i o l . Chem. (1970), 34, 700. Mulder, R., and G i j s w i j t , M. J., P e s t i c . S c i . (1973), 4, 737. Wellinga, Κ . , Mulder, R., and van Daalen, J . J., J . Agr. Food Chem. (1973), 21, 348. Wellinga, Κ . , Mulder, R., and van Daalen, J . J., J . Agr. Food Chem. (1973), 21, 993. Van Daalen, J . J . , Meltzer, J . , Mulder, R., and Wellinga Κ . , Naturwissenschaften (1972), 59, 312. Mulder, R., and Swennen, Α. Α . , Proc. 7th British I n s e c t i c i d e and Fungicide Conf. (1973), 729 E l i n g s , Η . , and Dieperink, J . G . , Mededelingen van de F a c u l t e i t Landbouwwetenschappen, Gent (1974), 39, 833. B i j l o o , J . D . , P h y t i a t r i e phytopharmacie (1975), 24, 147,

13.

10. 11.

12. 13. 14. Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch013

15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25· 26. 27. 28. 29. 30. 31. 32.

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Van Busschbach, E . J . , P h y t i a t r i e phytopharmacie (1975), 24, 159. Nölle, Η. Η . , Van Busschbach, E. J . , and Verloop, Α . , Mitteilungen aus der B i o l . Bundesanstalt f . Land- und Forstwirtschaft B e r l i n - Dahlem (1975) 165, 161. Ascher, K. R. S., and Nemny, Ν. Ε., Phytopara­ sitica (1974), 2, 131. T a f t , Η. Μ . , and Hopkins, A. R., J . Econ. Ento­ mol., (1975), 68, 551. Moore, J r . , R. F . , and T a f t , Η. M . , J . Econ. Entomol. (1975), 68, 96. C a r t e r , S. W., J . Stored Prod. Res. (1975), 11, 187. Holst, Η . , Z. f. P f l . Krankh. (1975), 82, 1. Wright, J . Ε . , and Spates, G. E., J. Econ. Ento­ mol. (1976), 69, 365. Grosscurt, A. C . , Mededelingen van de F a c u l t e i t Landbouwwetenschappen, Gent (1976), 41, ( i n press). Grosscurt, A. C . , paper i n p r e p a r a t i o n . F e r r e l l , C. D . , and Verloop, Α . , A b s t r . Pap., 170th Meet., Amer. Chem. Soc. (1975), PEST 35. Verloop, Α . , Hoogenstraaten, W., and T i p k e r , J . , Abstr. Pap., 167th Meet., Amer. Chem. Soc. (1974), CHLT 011. Verloop, Α . , i n "Drug Design" (E. J . A r i ë n s , e d . ) , V o l . 7 (1976), pp 255 - 311. Academic Press, New York. Verloop, Α . , and T i p k e r , J . , submitted to P e s t i c . Sci. T i p k e r , J . , Wellinga Κ . , and Verloop, Α . , Symposium P e s t i c i d e s Group, S . C . I . (London, Feb. 1977). Yu, C.-C., and Kuhr, R. J . , J . Agr. Food Chem. (1976), 24, 134. Verloop, Α . , Residue Reviews (1972), 43, 55. Nimmo, W. B . , and Verloop, Α . , Ζ. f. P f l . Krankh. (1975), V I I , 147. Verloop, Α . , Nimmo, W. Β., and De Wilde, P. C . , A b s t r . Pap., 8th I n t . Plant P r o t e c t i o n Congress, Moscow (1975). Verloop, Α . , Nimmo, W. B . , and De Wilde, P . C . , submitted to P e s t i c . S c i . Metcalf, R. L . , Lu, P . - Y . , and Bowlus, S., J. Agr. Food Chem. (1975), 23, 359. Nimmo, W. Β., Verloop, Α . , and De Wilde, P. C . , submitted to P e s t i c . S c i . Still, G. G . , personal communication.

270 33. 34. 35· 36. 37. 38.

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39. 40. 41. 42. 43. 44. 45. 46. 47·

48. 49· 50. 51.

PESTICIDE CHEMISTRY IN THE 20TH CENTURY Ruzo, L. O., Zabik, M. J., and Schuetz, R. D . , J . Agr. Food Chem. (1974), 22, 1106. De Wilde, P. C . , unpublished r e s u l t s , Philips— Duphar. Meltzer, J . , Houtman, A. C . , and Van der Kolk, B. J . , unpublished r e s u l t s , Philips-Duphar. Deul, D. Η., and Vos, C . , paper i n preparation. Still, G. G . , and Leopold, R. Α . , A b s t r . Pap., 170th. Meet., Amer. Chem. Soc. (1975), PEST 5. Metcalf, R. L . , Sanga, G. Κ . , and Kapoor, I. P . , Environm. S c i . Technol. (1971), 5, 709. Post, L. C . , and Willems, A. G. Μ., paper i n preparation. Post, L. C . , and Vincent, W. R., Naturwissenschaften (1973), 60, 431. Post, L. C . , De Jong, B. J . , and Vincent, W. R., Pest. Biochem. P h y s i o l . (1974),4,473. Deul, D. H., De Jong, B. J . , and Kortenbach, J . Α. Μ., submitted to Pest. Biochem. P h y s i o l . Ker, R. F . , J . Insect. P h y s i o l . , i n press. Hunter, Ε., and Vincent, J . F . , E x p e r i e n t i a (1974), 30, 1432. Deul, D. H. et al., unpublished. Ishaaya, I . , and Casida, J . Ε., Pest. Biochem. P h y s i o l . (1974), 4, 484. Marks, E . P . , and Sowa, Β . Α . , i n "Mechanism of P e s t i c i d e A c t i o n " (G. K. Kohn, e d . ) , ACS Sympo­ sium S e r i e s , V o l . 2 (1974), PP. 144 - 155, Amer. Chem. Soc., Washington, D.C. Sowa, Β . Α . , and Marks, E . P . , Insect Biochem. (1975), 5, 855. G i j s w i j t , M. J., Deul, D. Η . , and De Jong, B. J . , submitted to Pest. Biochem. P h y s i o l . Moreau, R., Castex, C . , and Lamy, Μ., Ann. Z o o l . E c o l . anim. (1975), 7, 161. Yu, S. J . , and T e r r i e r e , L . C . , L i f e S c i . (1975), 17, 619.

14 Fourth Generation Insecticides W. S. BOWERS

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch014

New York State Agricultural Experiment Station, Geneva, Ν. Y.

Following discovery of the insect juvenile hormones and their importance to insect development, agricultural scientists became excited about the possibility of using these hormones for insect control. The presence of the juvenile hormones (JH) throughout immature development and during adult l i f e was readily demonstrated by classical endocrinological techniques. It was soon shown that these hormones prevent precocious development during the larval and nymphal stages and that adult insects required JH in order to permit development of the ovaries. C. M. Williams (1) prepared the f i r s t active extract from the cecropia moth and showed that this extract prevented adult development when applied to insect pupae. Treated pupae molted into morphogenetic monsters and died. Treatment of other stages produced no ill effects. From these studies i t became clear that during the transformation of the immature insect into the adult (during the pupal stage) the juvenile hormones must be absent. This short developmental period is completely deranged when supplied with JH. Three juvenile hormones in Figure 1 were identified by Bowers et a l . (2), Roller et a l . (3), Meyer et a l . ( 4 ) , Judy et a l . ( 5 ) . Although the natural juvenile hormones soon proved to be too labile under f i e l d conditions, many analogs were prepared which in addition to increased s t a b i l i t y were much more active than the natural hormones, Bowers ( 6 ) , Pallos et al. (7), Slama et a l . ( 8 ) . Zoecon has registered one analog (9) for control of floodwater mosquitos and manure-breeding f l i e s . The overall utility of control of insects with JH, however, is limited to those insects which can be brought into contact with the hormones during their brief period of sensitivity ( i . e . pupal or last­ -stage nymph). Under most f i e l d conditions insects exist in all stages of development and all but the last developmental stages are unaffected by excess JH since these are stages which require JH. Taking a somewhat different view, we reasoned that since juvenile hormones are required throughout most of an insect's 271

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Figure 2.

Induction of precocious metamorphosis in the cotton stainer Dysdercus cingulatus with Precocene II

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l i f e , a more g e n e r a l l y u s e f u l method of i n s e c t c o n t r o l would be by preventing the s e c r e t i o n o f these hormones. Thus, a hormone antagonist should stop immature development and cause the i n s e c t to molt prematurely to an a d u l t . Likewise, an adult i n s e c t without j u v e n i l e hormone could not develop i t s ovaries and would be sterile. C e r t a i n adult i n s e c t s r e q u i r e JH f o r the production o f sex pheromones and might be rendered u n a t t r a c t i v e by a hormone antagonist. Insect diapause i n c e r t a i n l a r v a e (10) i s caused by an excess of JH, while adult diapause r e s u l t s from a lack o f JH (11, 12). I n t e r f e r i n g with the presence or absence o f JH during these stages could be d i s a s t r o u s f o r i n s e c t s . Our strategy f o r an endocrinologie approach to i n s e c t c o n t r o l t h e r e f o r e was based upon the search f o r a n t i - j u v e n i l e hormones. JH analogs have been found i n plants (.13, 14) so i t seemed p o s s i b l e that anti-hormones might a l s o e x i s t i n p l a n t s . We began t o extract p l a n t s with apolar solvents and t e s t e d these e x t r a c t s by contact and fumigation against the cotton s t a i n e r , Dysdercus c i n g u l a t u s , and the milkweed bug, Oncopeltus f a s c i a t u s . Eventually we found that the e x t r a c t o f the bedding p l a n t , Ageratum houstonianum, contained two potent a n t i - j u v e n i l e hormones. By contact and fumigation the e x t r a c t induced milkweed bug and cotton s t a i n e r nymphs to molt to t i n y a d u l t s , s k i p p i n g one or more o f t h e i r immature stages. These miniature adults d i d not reproduce and q u i c k l y died (Figure 2). Treatment o f adult females prevented ovarian development o r , i f developed ovaries were present at the time of treatment, the ovaries were caused t o regress to the undeveloped s t a t e . We were unable to induce precocious metamorphosis i n other i n s e c t Orders, but could s t e r i l i z e many of the adult stages by treatment with the e x t r a c t . I s o l a t i o n and i d e n t i f i c a t i o n o f the two n a t u r a l a n t i j u v e n i l e hormones revealed two simple chromenes; 7-methoxy-2,2dimethyl chromene and 6,7-dimethoxy-2,2-dimethyl chromene (Figure 3). Since these compounds induced precocious metamorphosis, we c a l l e d them Precocene I and II r e s p e c t i v e l y . Subsequently we found that both compounds had been p r e v i o u s l y i d e n t i f i e d and synthesized (JJ5, 16_, 17). We developed an e f f i c i e n t synthesis f o r these compounds^ shown i n Figure 4. In a d d i t i o n a l b i o l o g i c a l work we found that v i r g i n female American cockroaches, P e r i p l a n e t a americana, stopped producing t h e i r sex a t t r a c t a n t f o l l o w i n g treatment with Precocene I I , while milkweed bug and Mexican bean b e e t l e eggs t r e a t e d with Precocene II were unable to hatch. Normal non-diapausing Colorado potato b e e t l e s t r e a t e d with Precocene II promptly l e f t t h e i r food p l a n t s , burrowed i n t o the s o i l and entered diapause. A l l of these b i o l o g i c a l e f f e c t s o f the precocenes i n d i c a t e d that the s e c r e t i o n o f the j u v e n i l e hormones had been prevented. We t e s t e d t h i s hypothesis by t r e a t i n g i n s e c t s with both Precocene II and j u v e n i l e hormone. We found t h a t , when these compounds

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Precocene Figure 3.

/0

Precocene I I

I

Anti-juvenile hormones from Ageratum houstoni-

anum

PH

R

R = H,-OMe Figure 4. Synthesis of precocene. Reaction of an appropriate phenol with dimethyl acrylic acid and polyphosphoric acid (PPA) on the steam bath gives the chromanone in quantitative yield. Reduction with lithium aluminum hydride (LAH) and brief treatment with 4N hydrochloriic acid gives the chromene.

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were combined, milkweed bug nymphs developed normally, adult i n s e c t s developed t h e i r ovaries s u c c e s s f u l l y and produced v i a b l e eggs. Thus, the e f f e c t s o f the precocenes are f u l l y r e v e r s i b l e and confirm our hypothesis that they are a c t i n g to prevent the s e c r e t i o n o f the j u v e n i l e hormones. As p r e v i o u s l y s t a t e d , these compounds do not show a n t i j u v e n i l e hormone a c t i v i t y against a l l i n s e c t s , but open the door to a new mode o f i n s e c t c o n t r o l which a f f e c t s most i n s e c t stages and provides a broader dimension t o the e n d o c r i n o l o g i e s t r a t e g y of i n s e c t c o n t r o l . I f the j u v e n i l e hormones and t h e i r analogs are representa­ t i v e o f t h i r d - g e n e r a t i o n p e s t i c i d e s ( 1 8 ) , the a n t i - j u v e n i l e hormones may be considered i n a fourth-generation concept.

Literature Cited (1) Williams, C. Μ., Nature (1956) 178, 212. (2) Bowers, W. S., Thompson, M. J., Uebel, E. C . , Life Science (1965) 4, 2323. (3) R o l l e r , H. K . , Dahm, H., Sweeley, C. C . , Trost, Β. Μ., Angew. Chem. (1967) 79, 190. (4) Meyer, A. S., Schneiderman, Η. Α., Hanzman, Ε . , Ko, J . Η., Proc. N a t l . Acad. S c i . U. S. (1968) 60, 853. (5) Judy, K. J., Schooley, D. Α., Dunham, L. L . , H a l l , M. S., Bergot, B. J., S i d d a l l , J . B . , Proc. Natl. Acad. S c i . U. S. (1973) 70, 1509. (6) Bowers, W. S., Science (1969) 164, 323. (7) Pallos, F. Μ., Menn, J. J., Letchworth, P. Ε . , Miaullis,J.Β., Nature (1971) 232, 486. (8) Slama, Κ., Romanuk, Μ., Sorm, F . , "Insect Hormones and Bio­ -analogues" 477 pp., Springer Verlag, New York, 1974. (9) Hendrick, C. Α., S t a a l , G. B . , S i d d a l l , J . Β., J . Agr. Food Chem. (1973) 21, 354. (10) Chippendale, G. Μ., Y i n , C. Μ., Nature (1973) 246, 511. (11) de Wilde, J., De Boer, J . Α., J . Insect Physiol. (1961) 6, 152. (12) Bowers, W. S., Blickenstaff, C. C . , Science (1966) 154, 1673. (13) Bowers, W. S., Fales, Η. Μ., Thompson, M. J., Uebel, E. C . , Science (1966) 154, 1020. (14) Cerny, V., D i l e j s , L . , Labler, L . , Sorm, F . , Slama, Κ., Collect. Czech. Chem. Commun. (1967) 32, 3926. (15) Alertson, A. R., Acta. Chem. Scand. (1955) 9, 1725. (16) Huls, R., B u l l . Soc. Chim. Belg. (1958) 67, 22. (17) Livingstone, R., Watson, R. Β . , J . Chem. Soc. (1957) 1509. (18) Williams, C. M . , S c i . Amer. (1967) 217, (1) 13.

15 Post Harvest Responses and Plant Growth Regulators MORRIS L I E B E R M A N

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch015

Post Harvest Plant Physiology Laboratory, Beltsville Agricultural Research Center, Agricultural Research Service, U.S.D.A., Beltsville, Md. 20705

Regulation and control of post harvest metabolism with respect to ripening, aging, and senescence, has for many years been associated with degradation and the action of ethylene (1). Recent concepts and interpretations however, suggest that aging and senescence i n plant tissues are not only deteriorative processes but also developmental processes i n which other growth regulators play important roles (2). Thus, although ethylene is still considered a major influence on post harvest metabolism, the other plant hormones, the auxins, gibberellins, cytokinins, and abscisic acid, are also thought to s i g n i f i c a n t l y influence the aging process. Most likely, ethylene action results from interactions with these hormones. In this report I b r i e f l y review c l a s s i c a l observations on the effect of ethylene on post harvest tissues, especially those of f r u i t , and point out why ethylene was considered the ripening hormone. Secondly, I call attention to reasons for questioning ethylene as the exclusive ripening hormone and review recent data linking ethylene action to the action of other hormones and vice versa. F i n a l l y , I b r i e f l y discuss ethylene production and i n h i b i t i o n in plant tissue. These considerations may give r i s e to new concepts of controlling aging and senescence of plant tissues and of preserving crops after harvest. Physiological Responses to Ethylene. C l a s s i c a l l y , two types of f r u i t have been recognized with respect to their response to ethylene (I): (a) climacteric f r u i t , such as apples or avocado, which show an immediate r i s e i n respiration and an accelerated ripening rate when exposed to a few parts per m i l l i o n of ethylene; and (b) non-climacteric fruit, such as c i t r u s , which show a r i s e i n respiration during exposure to much higher concentrations of ethylene (100 ppm or more) then a return to the normal rate when ethylene is removed (Figure 1). Continuous application of such high levels of ethylene nevertheless accelerates ripening in non-climacteric fruit, which appear to r e s i s t reaction to ethylene (3). In contrast climacteric f r u i t 280

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Air Air-} ethylene _I

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L _ . - L _1_ ..L _L__J 10 12 14 16 18 20

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Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch015

Endeavor Figure 1. Effect of ethylene on respiration of climacteric and nonclimacteric fruit. Ethylene causes greatest response in climacteric fruit when applied to mature fruit prior to the climacteric rise. In nonclimacteric fruit high concentrations of ethylene stimuhte respiration for short time periods. This stimulation is observed at any time upon application of ethylene (3).

u s u a l l y r e q u i r e o n l y a f e w ppm o f e t h y l e n e t o t r i g g e r t h e r i p ­ ening process. E t h y l e n e was b e l i e v e d t o be t h e r i p e n i n g hormone, b e c a u s e i t i s a n a t u r a l m e t a b o l i t e , i s v i r t u a l l y absent i n mature b u t n o n - r i p e n i n g f r u i t , and i s p r o d u c e d i n i n c r e a s i n g amounts j u s t p r i o r t o the o n s e t o f r i p e n i n g . Furthermore, ethylene applied a t r e l a t i v e l y low c o n c e n t r a t i o n s c a n i n d u c e r i p e n i n g a n d a g i n g i n green mature f r u i t , a c c e l e r a t i n g , but not a l t e r i n g , t h e n a t u r a l p r o c e s s e s . Compared t o r e l a t e d compounds, e t h y l e n e i s unique i n i t s e f f e c t i v e n e s s i n i n d u c i n g r i p e n i n g and a g i n g (Table I ) .

T a b l e I . Comparative E f f e c t i v e n e s s o f E t h y l e n e and R e l a t e d A n a l o g u e s i n P e a S t e m - S e c t i o n A s s a y (From B u r g and Burg (4) Compound Ethylene Propylene Vinyl chloride Carbon Monoxide Acetylene 1-Butene

Relative Activity;Moles/unit 1 130 2,370 2,900 12,500 140,000

effectiveness

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Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch015

The c l i m a c t e r i c r i s e i n r e s p i r a t i o n i s c o n s i d e r e d a p o r t e n d of the s h i f t i n metabolism from anabolism to c a t a b o l i s m . This t r a n s i t i o n from the f u l l y mature s t a t e t o the r i p e n i n g s t a t e o c c u r s more s h a r p l y i n f a s t e r g r o w i n g f r u i t , s u c h as t h e a p p l e , i n w h i c h t h e r e i s h y d r o l y t i c c o n v e r s i o n o f s t a r c h t o s u g a r s and of i n s o l u b l e p e c t i n s t o s o l u b l e p e c t i n s . There i s a l s o a l o s s o f c h l o r o p h y l l , and a s y n t h e s i s o f a n t h o c y a n i n s , c a r o t e n o i d s and x a n t h o p h y l l s , as w e l l as o c c u r r e n c e o f o t h e r s u c h r e a c t i o n s a s s o c i a t e d w i t h r i p e n i n g . I n n o n - c l i m a c t e r i c f r u i t , s u c h as c i t r u s , w h i c h show no c o m p a r a b l e r i s e i n r e s p i r a t i o n o r e t h y l e n e p r o d u c t i o n , g r o w t h and d e v e l o p m e n t a r e p r o l o n g e d and r i p e n i n g o c c u r s o n l y on t h e t r e e . An o r a n g e r e q u i r e s 8-11 months f r o m f u l l b l o o m t o m a t u r i t y , i n c o n t r a s t t o an a p p l e , w h i c h may r e q u i r e o n l y 4-5 months (5^) . R e s i s t a n c e t o E t h y l e n e as a R i p e n i n g A g e n t . The c l a s s i c a l concept of r i p e n i n g , e s p e c i a l l y of c l i m a c t e r i c f r u i t , i s t h a t e t h y l e n e t r i g g e r s a c a s c a d e o f r e a c t i o n s l e a d i n g t o r i p e n i n g and aging. T h i s c o n c e p t has b e e n q u e s t i o n e d b e c a u s e s u c h a t r i g ­ g e r i n g phenomenon i s a b s e n t i n n o n - c l i m a c t e r i c f r u i t . Also, u n d e r some c o n d i t i o n s e t h y l e n e does n o t t r i g g e r f r u i t r i p e n i n g , e v e n i n c l i m a c t e r i c f r u i t (6). T h u s , f o r e x a m p l e , a v o c a d o s do n o t r i p e n on t h e t r e e , d e s p i t e t h e i r i n t e r n a l a t m o s p h e r e o f a b o u t 0.1 ppm e t h y l e n e , a c o n c e n t r a t i o n w h i c h c a n i n d u c e r i p e n i n g i n the h a r v e s t e d f r u i t . Even t r e a t m e n t of the u n h a r v e s t e d fruit w i t h 50 ppm e t h y l e n e f o r 48 h o u r s does n o t c a u s e r i p e n i n g . The r e s i s t a n c e t o r i p e n i n g by e t h y l e n e e x t e n d s t o n e w l y h a r v e s t e d avocado f r u i t . A p p l i c a t i o n o f 100 ppm e t h y l e n e 1 h o u r a f t e r h a r v e s t had no e f f e c t on r i p e n i n g (7^). However 24 h o u r s a f t e r h a r v e s t , ethylene treatment c o n s i d e r a b l y a c c e l e r a t e d r i p e n i n g , much as e x p e c t e d . Such d a t a gave r i s e t o t h e i d e a o f an " a n t i r i p e n i n g " i n h i b i t o r , w h i c h , p r e s u m a b l y , i s most a c t i v e i n t h e u n h a r v e s t e d f r u i t and d i s s i p a t e d a f t e r h a r v e s t . G r a p e s a l s o do n o t r e s p o n d t o e t h y l e n e as e x p e c t e d . In d e v e l o p m e n t o f t h e g r a p e 3 s t a g e s o f g r o w t h c a n be d i s t i n g u i s h e d . An e a r l y r a p i d e n l a r g e m e n t i s f o l l o w e d by a s l o w s t a g e o f g r o w t h w h i c h i s a g a i n f o l l o w e d by a r a p i d g r o w t h s t a g e . The grape r i p e n s d u r i n g the t h i r d stage but w i t h o u t i n c r e a s e i n e t h y l e n e p r o d u c t i o n ( F i g u r e 2 ) . However, a s h a r p i n c r e a s e i n a b s c i s i c a c i d (ABA) does o c c u r and i s c o r r e l a t e d w i t h r i p e n i n g of the b e r r y . While the s e n s i t i v i t y t o e t h y l e n e i n c r e a s e d d u r i n g r i p e n i n g o f t h i s f r u i t (9) i t i s a l s o p o s s i b l e t h a t e t h y l e n e i s not the major r i p e n i n g f a c t o r . Such examples o f " a n o m a l o u s " r i p e n i n g b e h a v i o r d a t a s u g g e s t that other f a c t o r s i n a d d i t i o n to ethylene s i g n i f i c a n t l y a f f e c t r i p e n i n g and s e n e s c e n c e . The e x p e r i m e n t s w i t h c i t r u s and a v o c a d o s u g g e s t a n t i - r i p e n i n g s u b s t a n c e s and t h e s t u d i e s w i t h t h e d e v e l o p i n g g r a p e s u g g e s t t h a t ABA may p l a y a r o l e i n t h e s e processes. However, ABA a p p e a r s t o be a s u b s t i t u t e o r s u p p l e m e n t t o e t h y l e n e and n o t a t r i g g e r i n g a g e n t ( 1 0 ) .

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch015

15.

LiEBERMAN

Post Harvest

DAYS

Responses

FROM

283

VERAISON Plant Physiology

Figure 2. Ethylene concentration in extracted gas, weight of abscisic acid (ABA), fresh weight and volume per berry in "Doradillo" grapes during the stationary and ripening stages of growth (pre and post veraison) (S)

Other F a c t o r s I n f l u e n c i n g R i p e n i n g and Aging. Tradition­ a l l y , p l a n t hormones a r e a s s o c i a t e d w i t h g r o w t h and d e v e l o p m e n t of young v i g o r o u s t i s s u e s . I t i s now e v i d e n t , h o w e v e r , t h a t t h e s e hormones ( a u x i n s , c y t o k i n i n s , g i b b e r e l l i n s a n d ABA) may a l s o be i m p o r t a n t t o r i p e n i n g , a g i n g a n d s e n e s c e n c e , a n d t o many other aspects o f post harvest metabolism. Conversely, ethylene, w h i c h was a s s o c i a t e d w i t h r i p e n i n g i n a g i n g c e l l s a n d t i s s u e s , appears a l s o t o p l a y an i m p o r t a n t r o l e i n young v i g o r o u s l y growing t i s s u e s (11). W i t h o u t i n any way d i m i n i s h i n g t h e i m p o r t a n c e o f e t h y l e n e i n the c o n t r o l and r e g u l a t i o n o f r i p e n i n g and a g i n g , I emphasize the c r i t i c a l s u p p l e m e n t a l importance o f a u x i n s , g i b b e r e l l i n s , and

284

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THE

20TH

CENTURY

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch015

c y t o k i n i n s , a l o n g w i t h ABA, i n t h e r i p e n i n g and a g i n g p r o c e s s e s i n post h a r v e s t t i s s u e s . R i p e n i n g , a g i n g , and s e n e s c e n c e o f p l a n t t i s s u e s and o r g a n s a r e d e v e l o p m e n t a l s t a g e s i n t h e l i f e c y c l e and, l i k e any o t h e r s t a g e i n g r o w t h and d e v e l o p m e n t , a r e r e g u l a t e d and c o n t r o l l e d , a t t h e o r g a n i z a t i o n a l l e v e l , by i n t e r ­ a c t i o n between e t h y l e n e and o t h e r p l a n t hormones. Evidence f o r Hormonal I n t e r a c t i o n s w i t h E t h y l e n e . There i s e v i d e n c e o f a n t a g o n i s m b e t w e e n a u x i n s , g i b b e r e l l i n s and c y t o k i n i n s on one hand and e t h y l e n e and ABA on t h e o t h e r ( 1 2 ) . The c o n t r o l o f f r u i t g r o w t h , d e v e l o p m e n t , r i p e n i n g and a g i n g may depend on t h e r e l a t i v e i m p o r t a n c e o f a s p e c i f i c hormone i n the t o t a l hormonal balance. V a r i o u s hormones may t e n d t o be d o m i n a n t o r l a t e n t d e p e n d i n g p r o b a b l y on t h e i r l e v e l s o r c o n ­ c e n t r a t i o n s a t a g i v e n stage of the l i f e c y c l e . F i g u r e 3 shows t h e h y p o t h e t i c a l k i n e t i c s o f g r o w t h , r e s p i r a t i o n and r e l a t i v e hormone l e v e l s i n a c l i m a c t e r i c f r u i t at d i f f e r e n t stages of i t s l i f e c y c l e . H y p o t h e t i c a l hormone l e v e l s d u r i n g d e v e l o p m e n t and r i p e n i n g h a v e b e e n s p e c u l a t e d on b e f o r e ( 1 3 ) . The r a t i o n a l e f o r t h i s o u t l i n e i s b a s e d on t h e known i n f l u e n c e s o f t h e v a r i o u s hormones on c e l l d i v i s i o n ,

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch015

15.

LiEBERMAN

Post Harvest

Responses

285

e l o n g a t i o n , and senescence. I n v e r y young f r u i t , c e l l d i v i s i o n i s t h e m a j o r a c t i v i t y , and, a u x i n s , g i b b e r e l l i n s a n d c y t o k i n i n s a r e a t t h e i r h i g h e s t l e v e l s , e t h y l e n e i s v i r t u a l l y a b s e n t , and ABA c o n t e n t i s r e l a t i v e l y h i g h ( 1 4 ) . The l e v e l s o f hormones r e f l e c t t h e i r a c t i v i t i e s which are presumably h i g h d u r i n g c e l l division. ABA may o p e r a t e as a b r a k e d u r i n g t h i s s t a g e b y opposing the p o s s i b l e e x c e s s i v e growth e f f e c t s o f h i g h con­ c e n t r a t i o n s o f some o f t h e s e hormones. A l s o , ABA i s somehow a l s o r e l a t e d t o w a t e r uptake w h i c h i s i m p o r t a n t i n young t i s s u e s (15). D u r i n g r a p i d c e l l e l o n g a t i o n g i b b e r e l l i n s may t e n d t o i n c r e a s e somewhat i n k e e p i n g w i t h t h e i r i m p o r t a n c e i n e l o n g a t i o n processes. During m a t u r a t i o n , t h e a u x i n s , g i b b e r e l l i n s , and c y t o k i n i n s d e c l i n e , r e a c h i n g v e r y low l e v e l s toward the end o f the m a t u r a t i o n p e r i o d . I t i s d u r i n g t h i s time t h a t t h e l e v e l s o f e t h y l e n e a n d ABA b e g i n t o r i s e , p r e c e d i n g somewhat t h e increase i n r e s p i r a t i o n associated with climacteric f r u i t . A l t h o u g h o n l y l i m i t e d d a t a a r e a v a i l a b l e o n endogenous hormone l e v e l s d u r i n g d i f f e r e n t s t a g e s o f f r u i t g r o w t h a n d d e v e l o p m e n t , some d a t a do s u p p o r t t h i s s i m p l i s t i c m o d e l . F o r example stem g r o w t h a p p e a r s t o r e s u l t f r o m a r i s e i n a u x i n l e v e l s (16) and r a t e o f tomato f r u i t r i p e n i n g i s i n v e r s e l y r e ­ l a t e d t o c y t o k i n i n content (17). Evidence f o r the i n t e r ­ r e l a t i o n s h i p s o f h o r m o n a l l e v e l s a n d r i p e n i n g and a g i n g i s a l s o o b t a i n e d f r o m e x p e r i m e n t s i n w h i c h v a r i o u s hormones a r e added t o r i p e n i n g o r aging f r u i t t i s s u e s . For example, t h e a u x i n , β-naphthylacetic a c i d , h a s l i t t l e e f f e c t o n c o l o r d e v e l o p m e n t i n r i p e n i n g banana p e e l d i s k s , w h e r e a s t h e c y t o k i n i n b e n z y l a d e n i n e c o n s i d e r a b l y r e t a r d s c o l o r i n g and, t h e r e f o r e , r i p e n i n g i n t h e s e d i s k s ( 1 8 ) . The t e n d e n c y o f exogenous a u x i n t o r e t a r d r i p e n i n g may be c o u n t e r b a l a n c e d b y t h e a b i l i t y o f a u x i n s t o s t i m u l a t e ethylene production. G i b b e r e l l i n s also retard r i p e n i n g (color f o r m a t i o n ) i n banana p e e l d i s k s , w h e r e a s a p p l i e d ABA a t 10"5 t o 10"^M a c c e l e r a t e s r i p e n i n g , as m i g h t be e x p e c t e d f r o m t h e known a n t a g o n i s m b e t w e e n ABA and g i b b e r e l l i n s ( 1 8 ) . The i n f l u e n c e o f g r o w t h hormones ( a u x i n s , c y t o k i n i n s , a n d g i b b e r e l l i n s ) a n d ABA o n e t h y l e n e p r o d u c t i o n i n a p p l e t i s s u e s l i c e s o f v a r i o u s s t a g e s o f m a t u r i t y b e f o r e , d u r i n g , and a f t e r t h e c l i m a c t e r i c r i s e i n r e s p i r a t i o n i s shown i n F i g u r e 4. P r e c l i m a c t e r i c t i s s u e s l i c e s , w h i c h e v o l v e v i r t u a l l y no e t h y l e n e , are s t r o n g l y i n h i b i t e d by the c y t o k i n i n , i s o p e n t e n y l adenosine ( I P A ) , i n d o l e a c e t i c a c i d ( I A A ) , and t o a l e s s e r e x t e n t b y g i b b e r e l l i c a c i d (GA). The e f f e c t o f a l l t h r e e hormones i s e v e n more i n h i b i t i n g t o e t h y l e n e p r o d u c t i o n b y t h e s e t i s s u e s . However, ABA s t i m u l a t e s e t h y l e n e p r o d u c t i o n i n p r e c l i m a c t e r i c t i s s u e slices. A t l a t e r s t a g e s i n t h e r i p e n i n g p r o c e s s , IAA and GA do n o t i n h i b i t e t h y l e n e p r o d u c t i o n a n d IAA may a c t u a l l y s t i m u l a t e . On t h e o t i i e r h a n d , IPA c o n s i s t e n t l y i n h i b i t s e t h y l e n e p r o d u c t i o n a t a l l s t a g e s o f r i p e n i n g t h r o u g h o u t t h e c l i m a c t e r i c and p o s t ­ c l i m a c t e r i c p e r i o d s . No g r e a t e r r e t a r d a t i o n i s a c h i e v e d b y a d d i t i o n o f GA a n d IAA t o IPA a t t h i s s t a g e .

286

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Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch015

Preclimactenc

CENTURY

Early climacteric rise

Figure 4. Influence of IAA, GA, cytokinin (IPA), and ABA, alone and in combinations, on ethylene production of pre-climateric, climacteric, and post-climateric apple tissue slices

•—control • —IAA • —GA A—IPA

O—ABA

Π — I A A + IPA Δ — I A A + IPA + G A

ABA s t i m u l a t e s e t h y l e n e p r o d u c t i o n i n p r e c l i m a c t e r i c and e a r l y c l i m a c t e r i c t i s s u e s l i c e s b u t s u b s e q u e n t l y has l i t t l e e f f e c t on e t h y l e n e p r o d u c t i o n i n a g i n g t i s s u e s l i c e s f r o m a p p l e s . These d a t a a l s o show t h a t t h e i n f l u e n c e o f a hormone may be c o n s i d e r a b l y a l t e r e d b y c o m b i n a t i o n s w i t h o t h e r hormones. Thus, IAA, w h i c h s t i m u l a t e s e t h y l e n e p r o d u c t i o n i n c l i m a c t e r i c and p o s t c l i m a c t e r i c t i s s u e does n o t s t i m u l a t e b u t i n h i b i t s when c o m b i n e d w i t h IPA a n d GA. F e e d b a c k R e l a t i o n s h i p B e t w e e n E t h y l e n e and O t h e r P l a n t Hormones. I f e t h y l e n e p r o d u c t i o n i n r i p e n i n g f r u i t i s an i n d e x o f a g i n g and s e n e s c e n c e , t h e n i t s s u p p r e s s i o n s h o u l d r e s u l t i n r e t a r d a t i o n , o r antagonism t o r i p e n i n g , a g i n g , and senescence.

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch015

15.

LiEBERMAN

Post Harvest

Responses

287

At t h e p r e c l i m a c t e r i c stage o f development, j u s t p r i o r t o t h e r i s e i n ethylene production,the concentrations of auxins, g i b b e r e l l i n s , a n d c y t o k i n i n s a r e assumed t o be v e r y l o w . A d d i t i o n o f l a r g e amounts o f t h e s e g r o w t h hormones t e n d t o s u p p r e s s e t h y l e n e p r o d u c t i o n . However, a f t e r e t h y l e n e p r o d u c t i o n s t a r t s and a c c e l e r a t e s , o n l y c y t o k i n i n c o n s i s t e n t l y s u p p r e s s e s ethylene p r o d u c t i o n . This suggests a s p e c i a l antagonism be­ tween c y t o k i n i n s and e t h y l e n e p r o d u c t i o n . T h i s a n t a g o n i s m i s c o n s i s t e n t w i t h t h e w e l l known r e t a r d a t i o n e f f e c t o f c y t o k i n i n s on l o s s o f c h l o r o p h y l l and p r o t e i n i n a g i n g l e a v e s ( 1 9 ) . The r e l a t i v e l a r g e s c a l e p r o d u c t i o n o f e t h y l e n e b y a g i n g t i s s u e s , a f t e r the r i p e n i n g r e a c t i o n s a r e f u l l y i n motion, r a i s e s t h e q u e s t i o n as t o w h e t h e r o r n o t c o n t i n u o u s p r e s e n c e o f e t h y l e n e i s n e c e s s a r y f o r t h e p r o g r e s s o f a g i n g and s e n e s c e n c e . F a i r l y l a r g e amounts o f e t h y l e n e a r e p r o d u c e d e v e n f r o m f u l l y senescent t i s s u e s . This might suggest a l o s s o f c o n t r o l over e t h y l e n e p r o d u c t i o n . Such a n i n t e r p r e t a t i o n w o u l d mean t h a t e t h y ­ lene produced by post c l i m a c t e r i c t i s s u e i s a by-product o f ag­ i n g metabolism wherein c o n t r o l o f hormonal s y n t h e s i s i s l o s t . However, t h e f a c t t h a t e t h y l e n e p r o d u c t i o n i n p o s t - c l i m a c t e r i c t i s s u e s c a n be s u p p r e s s e d b y a c y t o k i n i n s u g g e s t s t h a t i t i s a l w a y s u n d e r p h y s i o l o g i c a l c o n t r o l and h o r m o n a l l y r e g u l a t e d . Scheme f o r I n t e r r e l a t i o n s h i p b e t w e e n E t h y l e n e a n d O t h e r Hormones. From t h e s e d a t a and o t h e r s p r e s e n t e d b e l o w , one c a n a r r i v e a t a s i m p l e scheme f o r t h e a n t a g o n i s t i c and s u p p o r t i v e r e l a t i o n s h i p s o f t h e s e hormones i n m e t a b o l i s m . F i g u r e 5 shows h y p o t h e t i c a l i n t e r c o n n e c t i o n s between t h e v a r i o u s hormones as t h e y r e l a t e t o c e l l d i v i s i o n , g r o w t h , d e v e l o p m e n t and senescence d u r i n g the l i f e c y c l e o f a p l a n t o r organ. Two c a t e g o r i e s o f hormones may be d i s t i n g u i s h e d : ( 1 ) t h e a u x i n s ^ g i b b e r e l l i n s , and c y t o k i n i n s , w h i c h a r e m a i n l y a s s o c i a t e d w i t h growth and development by r e g u l a t i n g c e l l d i v i s i o n , e n l a r g e ­ ment and m a t u r a t i o n , and (2) e t h y l e n e a n d ABA, w h i c h g e n e r a l l y t e n d t o oppose o r a n t a g o n i z e t h e a c t i v i t i e s o f c a t e g o r y 1 h o r ­ mones and t o f u n c t i o n m a i n l y i n s e n e s c e n c e and a g i n g . During g r o w t h and d e v e l o p m e n t c a t e g o r y 2 hormones may oppose t h e e x c e s s i v e a c t i o n s o f c a t e g o r y 1 hormones, w h i c h may o t h e r w i s e c a u s e d i s t o r t e d and a b n o r m a l g r o w t h e f f e c t s . These hormones may e x i s t i n f e e d b a c k l o o p s . A u x i n s a r e known t o s t i m u l a t e e t h y l e n e p r o d u c t i o n (20) and, c o n v e r s e l y , e t h y l e n e i s known t o r e d u c e a u x i n l e v e l s (21) ( 2 2 ) . G i b b e r e l l i n s and ABA a r e known t o oppose e a c h o t h e r i n t h e i r i n f l u e n c e on i n d u c t i o n o f α-amylase s y n t h e s i s i n t h e b a r l e y a l e u r o n e l a y e r ( 2 3 ) . C y t o k i n i n s and ABA a r e known t o oppose e a c h o t h e r i n t r a n s p i r a t i o n phenomena w i t h r e s p e c t t o r e g u l a t i n g o p e n i n g and c l o s i n g o f s t o m a t a ( 2 4 ) . C y t o k i n i n i s known t o b o t h s t i m u l a t e (25) and d e p r e s s ( 2 6 ) e t h y l e n e p r o d u c t i o n i n p l a n t s . I do n o t know o f a n o p p o s i n g a c t i o n o f e t h y l e n e on c y t o k i n i n s y n t h e s i s o r a c t i v i t y b u t s u c h may v e r y l i k e l y e x i s t .

288

PESTICIDE C H E M I S T R Y IN T H E 2 0 T H

CENTURY

INTERACTIONS BETWEEN PLANT HORMONES

FEEDBACK

LOOPS

CATEGORY 2

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch015

CATEGORY I

->CELL

ETHYLENE

DIVISION <

/^GROWTH AND DEVELOPMENT<

\

CYTOKININS • SENESCENCE «

ABA

Figure 5. Hypothetical scheme of linkages and feedback relationships between category 1 and category 2 plant hormones related to their overall influences on growth, development, maturation, and senescence

The a n t a g o n i s m b e t w e e n g i b b e r e l l i n s a n d e t h y l e n e has been w e l l documented. F o r e x a m p l e , t h e y a r e a n t a g o n i s t i c i n r e g u l a t ­ i n g t h e g r o w t h o f c e l l s i n t h e subhook r e g i o n o f e p i c o t y l s o f e t i o l a t e d s e e d l i n g s ( 2 7 ) . Whereas GA a t lO'^M c a u s e s e x c e s s i v e c e l l e l o n g a t i o n a n d e t h y l e n e a t 0.5 ppm w h i c h c a u s e s t h e f o r m a ­ t i o n o f i s o d i a m e t r i c , s h o r t , squat c e l l s , the c o m b i n a t i o n o f b o t h hormones r e s u l t s i n t h e f o r m a t i o n o f a l m o s t n o r m a l s h a p e d c e l l s . Another type o f hormonal i n t e r a c t i o n i s i l l u s t r a t e d by the c o m p l e m e n t a r y o r s u p p l e m e n t a r y e f f e c t s o f two c a t e g o r y - 1 hormones on a p p l e shape a n d s i z e . The t r e a t m e n t o f N o r t h C a r o l i n a Red D e l i c i o u s a p p l e s (grown i n warm S p r i n g w e a t h e r ) w i t h g i b b e r e l l i n s A^ and Ay a n d a c y t o k i n i n ( a b o u t 25 ppm e a c h ) j u s t a f t e r f u l l b l o o m , c a u s e s them t o d e v e l o p m o r p h o l o g i c a l l y l i k e N o r t h w e s t Red D e l i c i o u s a p p l e s (grown i n c o o l S p r i n g w e a t h e r ) . The e x c e s s c y t o k i n i n s i n c r e a s e s c e l l d i v i s i o n i n t h e c a l y x l o b e s , and t h e g i b b e r e l l i n s accentuate e l o n g a t i o n o f the f r u i t . The f i n a l p r o d u c t i s an e l o n g a t e d f r u i t w i t h w e l l d e v e l o p e d c a l y x l o b e s , i n c o n t r a s t t o the s h o r t e r and f l a t t e r f r u i t o b t a i n e d w i t h o u t hormonal treatment (28).

15.

LiEBERMAN

Post Harvest

289

Responses

The s p e c i f i c mode o f a c t i o n o f t h e s e hormones a t t h e m o l e c u l a r l e v e l i s unknown. However, a s c i e n c e o f P l a n t P h a r m a c o l o g y i s d e v e l o p i n g b a s e d on a c o n c e p t i o n a l understanding o f t h e known e f f e c t s o f p l a n t hormones and t h e i r i n t e r a c t i o n s . An example o f p l a n t p h a r m a c o l o g y i s shown i n T a b l e I I , w h e r e i n a c o m b i n a t i o n o f c o m m e r c i a l g r o w t h r e g u l a t o r s was u s e d t o r e ­ i n f o r c e and a n t a g o n i z e e a c h o t h e r s a c t i o n , and t h e r e b y p r o d u c e a desired effect.

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch015

T a b l e I I E f f e c t o f E t h e p h o n , A l o n e and i n C o m b i n a t i o n s w i t h D a m i n o z i d e and A u x i n , on A b s c i s s i o n , F i r m n e s s a n d c o l o r o f M c i n t o s h A p p l e s (From E d g e r t o n and B l a n p i e d (29)) 1 Treatment Daminozide Daminozide + Ethephon D a m i n o z i d e + Ethephon+TP Control

Harvest Date Sept.24,1968 Sept.24,1968 Sept.24,1968 Sept.24,1968

Drop

% 2 77 3 29

Firm (lb) 16.3 15.5 14.7 14.5

Red Color % 56 67 91 51

1/ D a m i n o z i d e a p p l i e d a t 2000 ppm on Aug. 9, 1968. E t h e p h o n a p p l i e d a t 250 ppm on S e p t . 1 5 , 1968 TP a p p l i e d a t 20 ppm on S e p t . 1 5 , 1968 Daminozide ( s u c c i n i c a c i d 2,2-dimethyl h y d r a z i d e ) i s a g r o w t h r e t a r d a n t w h i c h a n t a g o n i z e s e t h y l e n e i n some r e a c t i o n s but a l s o tends t o r e i n f o r c e other ethylene e f f e c t s . Applied to m a t u r e a p p l e s on t h e t r e e , d a m i n o z i d e r e d u c e s f r u i t d r o p and increases firmness. These e f f e c t s i n d i c a t e r e t a r d a t i o n o f ripening. However, r e d c o l o r f o r m a t i o n i s a l s o i n c r e a s e d , w h i c h i s an e f f e c t a s s o c i a t e d w i t h a c c e l e r a t e d r i p e n i n g . When d a m i n o z i d e i s a p p l i e d w i t h e t h e p h o n , a n e t h y l e n e - f o r m i n g com­ pound [ ( 2 - c h l o r o e t h y l ) p h o s p h o n i c a c i d ] r e d color formation i s f u r t h e r enhanced, b u t f r u i t drop i s c o n s i d e r a b l y i n c r e a s e d . By a d d i t i o n o f an a u x i n , T P [ ( 2 , 4 , 5 - t r i c h l o r o p h e n o x y ) p r o p i o n i c acid] t o t h e s p r a y , f r u i t d r o p i s a l m o s t c o m p l e t e l y e l i m i n a t e d and r e d c o l o r i s enhanced e v e n more ( 2 9 ) • T h u s , t h e s e p l a n t g r o w t h r e g u l a t o r s , w h i c h may be c o n s i d e r e d t o r e p r e s e n t e t h y l e n e , a u x i n , and a compound t h a t a p p e a r s t o have c h a r a c t e r i s t i c s o f b o t h hormones, t h e d e s i r e d measure o f r e t a r d a t i o n and a c c e l e r a t i o n o f r i p e n i n g was o b t a i n e d . P r o d u c t i o n and I n h i b i t i o n o f E t h y l e n e . Now I w o u l d l i k e t o i l l u s t r a t e how k n o w l e d g e a b o u t a p l a n t hormone c a n be u s e d t o c o n t r o l and r e g u l a t e i t s a c t i o n . M e t h i o n i n e i s t h e p r e c u r s o r o f e t h y l e n e i n p l a n t t i s s u e s ( 3 0 ) . T h e r e f o r e , any compound w h i c h b l o c k s m e t h i o n i n e m e t a b o l i s m m i g h t be e x p e c t e d t o i n h i b i t ethylene b i o s y n t h e s i s . Rhizobitoxine was r e c o g n i z e d as an i n h i b i t o r o f m e t h i o n i n e b i o s y n t h e s i s (31) as were i t s a n a l o g u e s shown i n F i g u r e 6 ( 3 2 ) . 9

PESTICIDE C H E M I S T R Y IN T H E 2 0 T H

290

CENTURY

H

(1)

C H - C H - C1 H o - 0 - C * C - C H - C 0 0 H I I ! I 9

NH

OH

H NH

2

2

L-2-amino-4-(2-amino-3-hydroxypropoxy)-trans-3-butenoic (Rhizobitoxine)

acid

H (2) CH -CHo-0-è^C-CH-C00H 9

NH

H NH

2

2

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch015

L-2-amino-4-(2-aminoethoxy)-trans-3-butenoic

acid

H

(3)

CHo-0-fcsC-ÇH-COOH ή

3

tiH

2

L-2-amino-4-methoxy-trans-3-butenoic

(4)

acid

CH S-CH CH -CH-C00H 3

2

2

L-Methionine Figure 6.

Enol ether substituted amino acid analogues of methionine which are inhibi­ tors of ethylene production in plants

These e n o l e t h e r - s u b s t i t u t e d amino a c i d s a r e n a t u r a l p r o d u c t s i s o l a t e d from the f e r m e n t a t i o n b r o t h s o f Rhizobium japonicum ( r h i z o b i t o x i n e ) ( 3 1 ) , Pseudomonas a e r u g i n o s a (methoxy a n a l o g u e ) (33) a n d a s p e c i e s o f S t r e p t o m y c e s ( e t h o x y a n a l o g u e ) ( 3 4 ) . Apple f r u i t , i n f i l t r a t e d w i t h r h i z o b i t o x i n e and s t o r e d a t 0 f o r 11 w e e k s , e x h i b i t e d much r e d u c e d e t h y l e n e p r o d u c t i o n a n d r e s p i r a t i o n ( 3 5 ) . T h i s s t r o n g l y s u g g e s t s t h a t r i p e n i n g and a g i n g o f t h e f r u i t was r e t a r d e d b y t h e i n h i b i t i o n o f e t h y l e n e production. A g i n g was a l s o r e t a r d e d i n o r c h i d s h e l d i n s o l u t i o n s o f t h e e t h o x y a n d methoxy a n a l o g u e s . These experiments suggest t h a t m e t a b o l i c b l o c k s o f the b i o s y n t h e s i s o f e t h y l e n e c a n r e t a r d the a g i n g p r o c e s s . However, i n some t i s s u e s , s u c h as t o m a t o e s , r h i z o b i t o x i n e does n o t b l o c k a l l e t h y l e n e p r o d u c t i o n . T h e r e i s an i n d i c a t i o n o f a s e c o n d pathway o f e t h y l e n e p r o d u c t i o n o r a means o f c i r c u m v e n t i n g t h e r h i z o b i t o x i n e b l o c k . Therefore, t h e r e i s the n e c e s s i t y f o r an a d d i t i o n a l c h e m i c a l t o b l o c k e i t h e r t h e s e c o n d pathway o r t h e r o u t e a r o u n d t h e e t h y l e n e b l o c k . Perhaps a c o m b i n a t i o n o f r h i z o b i t o x i n e , c y t o k i n i n , and a f r e e r a d i c a l quencher c a n a c t t o r e t a r d the a g i n g process i n p l a n t s .

15.

LIEBERMAN

Post Harvest

Responses

291

I b e l i e v e a g r i c u l t u r a l c h e m i s t r y i n the next c e n t u r y w i l l e n t e r a new e r a i n w h i c h t h e s c i e n c e o f P l a n t P h a r m a c o l o g y w i l l be d e v e l o p e d . From k n o w l e d g e o f t h e mode o f a c t i o n o f t h e p l a n t hormones a s e r i e s o f compounds a n d c o m b i n a t i o n s o f t h e s e w i l l be f o r m u l a t e d t o c o n t r o l a n d r e g u l a t e p l a n t g r o w t h and d e v e l o p ­ ment, f o r human n e e d s .

Literature Cited

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch015

1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23.

Biale, J.B., Advances in Food Research (1960) 10, 293-354. Lieberman, Μ., Physiol. Vegetale (1975) 13, 489-499. Biale, J.B. and Young, R.E., Endeavour (1962) 21, 164-174. Burg, S.P. and Burg, E.A., Science (1965) 148, 1190-1196. Monselise, S.P., "Colloque Intern. C.N.R.S. No. 238, Facteurs et Regulation De La Maturation Des Fruits 97-103, Paris (1975). Coombe, B.G., Annual Review of Plant Physiol. (1976) 27, 507-528. Gazit, S., Jour. Amer. Soc. Hort. Science (1970) 95, 229-231. Coombe, B.G. and Hale, C.R., Plant Physiol. (1973) 51, 629-634. Hale, C.R., Coombe, B.G., and Hawker, J.S., Plant Physiol. (1970) 45,620-623. Tingua, P.O. and Young, R.E., Plant Physiol. (1975) 55, 937-940. Zimmerman, R.H., Lieberman, Μ., and Broome, O.C., Plant Physiol. (1976) (in press). Lieberman, M. and Kunishi, A.T. in "Plant Growth Substances 1970" edited by D.J. Carr, 549-560, Springer-Verlag, Berlin, 1971. Dilley, D.R., HortScience (1969) 4, 111-114. Powell, L.E. HortScience (1970) 5, 326. Hiron, R.W.P. and Wright, S.T.C.,Jour. Expt. Botany (1973) 24,769-781. Hatcher, E.S.J., Ann. Botany (1959) 23,409-423. Varga, A. and Bruinsma, J., Jour. Hort. Science (1974) 49, 135-142. Bruinsma, J., Knegt, Ε . , and Varga, A. in Colloque Intern. C.N.R.S. No. 238, Facteurs et Regulation De La Maturation Des Fruits, 193-198, Paris (1975). Richmond, A.E. and Lang, A. Science (1957) 125, 650-651. Lieberman, Μ., and Kunishi, A.T. Plant Physiol. (1975) 55, 1074-1078. Michener, H.D., Amer. Jour. Botany (1938) 25 711-720. Valdovinos, J.G., Ernest, L.C. and Henry, E.W. Plant Physiol. (1967) 42, 1803-1806. Chrispeels, M.J. and J.E. Varner. Nature (1966) 212, 10661067.

292 24. 25. 26. 27. 28. 29.

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30. 31. 32. 33. 34. 35.

PESTICIDE CHEMISTRY IN THE 20TH CENTURY Mizrahi, Y., Blumenfeld, Α., Richmond, A.E. Plant Physiology (1970) 46, 169-171. Fuchs, Y. and Lieberman, M. Plant Physiol. (1968) 43, 2029-2036. Lieberman, M. and Sloger, M. Plant Physiol.(1975) 56, 56 (Supplement). Stewart, R.N., Lieberman, M. and Kunishi, A.T., Plant Physiol. (1974) 54, 1-5. Williams, M.W. and Stahly, E.A., Jour. Amer. Soc. Hort. Sci. (1969) 94, 17-18. Edgerton, L.J. and Blanpied, G.D.,Jour. Amer. Soc. Hort. Science (1970) 95, 664-666. Lieberman, Μ., Kunishi, A.T. Mapson, L.W. and Wardale, D.A., Plant Physiol. (1966) 41, 376-382. Owens, L.D., Science (1969) 165, 18-25. Owens, L.D., Lieberman, M. and Kunishi, A.T. Plant Physiol. (1971) 48, 1-4. Scannell, J.P., Pruess, D.L., Denny, T.C., Sells, L.H., Williams, T. and Stempel, A., The Jour, of Antibiotics (1972) 25, 122-127. Pruess, D.L., Scannell, J.P., Kellett, Μ., Ax, H.A., Jancek, J., Williams, T.H. and Stempel, Α., The Jour. of Antibiotics (1974) 27, 229-233. Lieberman, Μ., Kunishi, A.T. and Owens, L.D., Colloque Internation. C.N.R.S. No. 238 "Facteurs et Regulation De La Maturation Des Fruits" 161-170, Paris (1975).

16 G r o w t h Regulators i n F l o w e r i n g and F r u i t Development L. C. LUCKWILL

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch016

Long Ashton Research Station, University of Bristol, England

Some of the earliest practical applications of growth regulators related to flowering and fruit development and many of the pioneers were American. Prominent amongst them were Felix Gustafson of Ann Arbor, Michigan, who in 1936 was the first to induce parthenocarpic fruits with auxins; Gardner, Marth and Batjer of the USDA who in 1939 pioneered the use of 1-naphthalene-acetic acid for pre-harvest drop control in apples - a method still in regular use today; and Clark and Kerns in Hawaii who used the same substance in 1942 to induce synchronous flowering in pineapples. In general, plant growth regulators mimic the action of genes and their special value and significance in the perennial fruit crops is that they enable us to do today what might take decades or even centuries to accomplish by conventional breeding techniques. Most pomologists would agree that i t would be highly desirable, and technically feasible, to breed an apple variety that would set fruit without pollination, that would not be subject to biennial bearing or need thinning, whose fruits would not drop from the tree before harvest, which could be readily propagated from cuttings and, above a l l , one that would partition a greater proportion of its assimilates into fruit, as opposed to vegetative growth. No one, however, is likely to embark on such an ambitious project because of the enormous time scale involved and the impossibility of predicting the needs of the industry that far ahead. So we are left with the alternative of using growth regulators to overcome the present genotype deficiencies of the crop - a subject which forms the central theme of this review. Flower Initiation The most obvious genotypic deficiency of the apple is the tendency to produce light and heavy crops in alternate years. 293

294

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CENTURY

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch016

T h i s phenomenon, w h i c h v a r i e s i n i n t e n s i t y i n d i f f e r e n t varieties, i s c h a r a c t e r i s t i c o f many o t h e r p e r e n n i a l f r u i t c r o p s i n w h i c h f l o w e r i n i t i a l s a r e l a i d down i n t h e summer o f t h e y e a r b e f o r e flowering. The s p a r s e f l o w e r i n d u c t i o n w h i c h a c c o m p a n i e s a h e a v y c r o p was f o r m e r l y a t t r i b u t e d t o d e p l e t i o n o f t h e c a r b o ­ h y d r a t e and n i t r o g e n o u s r e s e r v e s o f t h e t r e e : but, whilst a l t e r n a t e b e a r i n g may h a v e d e v e l o p e d a s a means b y w h i c h t h e t r e e c o u l d c o n s e r v e i t s f o o d r e s e r v e s , t h e c o n t r o l mechanisms a r e c l e a r l y hormonal i n n a t u r e . L e a v e s promote f l o w e r i n d u c t i o n . A s i n so many b i o l o g i c a l p r o c e s s e s a b a l a n c e o f a p r o m o t e r and a n i n h i b i t o r seems t o be involved. I n t h e pome f r u i t s t h e f l o w e r p r o m o t i n g i n f l u e n c e comes f r o m t h e r o s e t t e o f l e a v e s s u b t e n d i n g t h e t e r m i n a l b u d i n which i n i t i a t i o n occurs. The g r e a t e r t h e t o t a l a r e a o f t h e s u b ­ t e n d i n g l e a v e s , the g r e a t e r the chance of the bud becoming f l o r a l . I n p l a n t s where f l o w e r i n g i s i n d u c e d b y t h e p h o t o p e r i o d t h e r e i s s t r o n g evidence t h a t , a f t e r i n d u c t i o n by the c r i t i c a l dark p e r i o d t h e l e a v e s p r o d u c e a f l o w e r i n g hormone w h i c h , however, has n e v e r b e e n u n e q u i v o c a l l y i s o l a t e d and i d e n t i f i e d . Although f l o w e r i n g i s n o t i n d u c e d by p h o t o p e r i o d i n t h e a p p l e , i t i s p o s s i b l e t h a t t h e same o r a s i m i l a r t y p e o f s u b s t a n c e i s p r o d u c e d . A n o t h e r p o s s i b i l i t y , y e t t o be e x p l o r e d , i s t h a t l e a v e s f u n c t i o n o n l y i n d i r e c t l y i n f l o w e r i n d u c t i o n b y a i d i n g t h e movement i n t o t h e s p u r o f hormones c a r r i e d i n t h e t r a n s p i r a t i o n s t r e a m . The most l i k e l y t y p e o f hormones t o be i n v o l v e d h e r e w o u l d be t h e g r o u p o f s u b s t i t u t e d a m i n o p u r i n e s known as c y t o k i n i n s , p a r t i c u ­ l a r l y zeatin (6-(4-hydroxy-3-methylbut-2-enyl)-aminopurine) and i t s r i b o t i d e , w h i c h a r e b e l i e v e d t o o r i g i n a t e i n t h e r o o t a n d a^e f o u n d i n r e l a t i v e l y h i g h c o n c e n t r a t i o n s i n the xylem sap, p a r ­ t i c u l a r l y i n t h e e a r l y p a r t o f t h e s e a s o n (_2). There i s , as y e t , no d i r e c t e v i d e n c e t h a t f l o w e r i n i t i a t i o n i n a p p l e c a n be p r o m o t e d by a p p l i e d c y t o k i n i n s , t h o u g h i t i s o f i n t e r e s t t o n o t e t h a t i n P e r i l l a Beever and Woolhouse found increases i n c y t o k i n i n produced i n the r o o t s at the time of f l o r a l i n d u c t i o n . R a t h e r s t r o n g e r e v i d e n c e o f c y t o k i n i n i n v o l v e m e n t came f r o m M u l l i n s (4) who showed t h a t , i n t h e a b s e n c e o f r o o t s , i n f l o r e s ­ c e n c e d e v e l o p m e n t i n g r a p e v i n e s c a n be s t i m u l a t e d b y t h e a p p l i ­ c a t i o n o f β - b e n z y l a m i n o p u r i n e (BAP) and 6 - ( b e n z y l a m i n o ) - 9 - ( 2 t e t r a h y d r o p y r a n y l ) - 9 H - p u r i n e ( P B A ) , a n d f r o m Skene (j?) who f o u n d t h a t chlor m equat , w h i c h promotes f l o w e r i n i t i a t i o n i n the v i n e , a l s o i n c r e a s e s t h e c o n c e n t r a t i o n o f endogenous c y t o k i n i n i n t h e bleeding sap. M o n s e l i s e a n d H a l e v y ( 6 ) h a v e shown t h a t b e n z o t h i a z o l e - 2 - o x y a c e t a t e , a compound w i t h c y t o k i n i n - l i k e p r o p e r t i e s , t h o u g h d i f f e r e n t i n c h e m i c a l s t r u c t u r e , w i l l promote f l o w e r i n g i n Citrus. However, the p r e s e n t e v i d e n c e f o r the i n v o l v e m e n t o f c y t o k i n i n s i n f l o w e r i n i t i a t i o n i n pome f r u i t s , l i k e t h a t f o r t h e e x i s t e n c e of a s p e c i f i c f l o w e r i n g hormone, remains circumstantial and f u r t h e r e x p e r i m e n t a l e v i d e n c e i s n e e d e d .

16.

LUCKWiLL

Flowering

and Fruit

295

Development

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch016

Seeds i n h i b i t f l o w e r i n d u c t i o n . The d a t a o f H u e t (j) i l l u s t r a t e the e f f e c t of leaves i n promoting f l o w e r i n i t i a t i o n i n the s e e d l e s s W i l l i a m s ( B a r t l e t t ) p e a r . Although normally seedless i n warm c l i m a t e s t h i s p e a r w i l l p r o d u c e s e e d s i f c r o s s - p o l l i n a t e d , a n d t h e same e x p e r i m e n t i l l u s t r a t e s t h e d r a m a t i c e f f e c t w h i c h these seeds have i n i n h i b i t i n g f l o w e r i n i t i a t i o n . T h i s e f f e c t of s e e d s was f i r s t n o t e d b y Tumanov a n d G a r e e v ( δ ) , a n d c o n f i r m e d b y t h e w o r k o f Chan a n d C a i n (_9). L u c k w i l l (1 Oj s u g g e s t e d t h a t t h e e f f e c t was due t o e n d o g e n o u s g i b b e r e l l i n s w h i c h a r e p r e s e n t i n v e r y h i g h c o n c e n t r a t i o n s i n seeds at c e r t a i n s t a g e s of development. E v i d e n c e t h a t g i b b e r e l l i n s a r e t h e o p e r a t i v e hormones i n v o l v e d i s p a r t l y i n d i r e c t and p a r t l y d i r e c t . Indirect evidence comes f r o m t h e o b s e r v a t i o n t h a t y o u n g f r u i t l e t s o n l y become i n h i b i t o r y t o f l o r a l i n i t i a t i o n a t 5 t o 6 weeks a f t e r f u l l b l o o m , w h i c h i s a l s o t h e t i m e t h e y s t a r t t o p r o d u c e l a r g e amounts o f GA4 a n d G A 7 (1θ): (11 ) , a n o b s e r v a t i o n , i n c i d e n t a l l y , w h i c h e x p l a i n s why f r u i t t h i n n i n g n e e d s t o be done w i t h i n t h i s t i m e l i m i t i f r e t u r n b l o o m f o r t h e f o l l o w i n g y e a r i s t o be i n c r e a s e d (Table i ) . The d i r e c t e v i d e n c e i s t h e f a c t t h a t i n a p p l e a n d many o t h e r s p e c i e s ( s t r a w b e r r y , p l u m , c h e r r y , p e a r , a l m o n d , a p r i c o t , orange, Fuchsia) sprays of g i b b e r e l l i c a c i d a p p l i e d s h o r t l y a f t e r bloom w i l l reduce or c o m p l e t e l y i n h i b i t f l o w e r i n g the f o l l o w i n g y e a r . T h i s i n h i b i t i n g e f f e c t o f GA o n f l o w e r TABLE Apple cv. different

I

Emneth E a r l y . E f f e c t o f f r u i t r e m o v a l a t t i m e s on f l o w e r i n i t i a t i o n i n b o u r s e b u d s

N o . o f weeks a f t e r f u l l b l o o m when t r e e s were d e - f r u i t e d

No. o f f r u i t buds f o r m e d a s fo o f t h o s e the p r e v i o u s y e a r

0 2

123

4 6 8

150 59 11

10

8 6

Not d e - f r u i t e d

146

G i b b e r e l l i n content of seeds μg GA3/IOOO s e e d s

< 1 .0 < 1 .0 3.2 19.2 27.1

—

i n i t i a t i o n appears i n d i r e c t c o n t r a s t to i t s r o l e i n l o n g day r o s e t t e type p l a n t s ( e . g . cabbage, r a d i s h , l e t t u c e , e t c . ) in w h i c h GA w i l l p r o m o t e f l o w e r i n g u n d e r n o n - i n d u c t i v e c o n d i t i o n s . The g e n e r a l s i t u a t i o n seems t o be t h a t g i b b e r e l l i n p r o m o t e s i n d u c t i o n i n t h o s e s p e c i e s w h i c h f l o w e r on l o n g s h o o t s , b u t i n h i b i t s i t i n s p e c i e s w h i c h f l o w e r on s h o r t s h o o t s , s u g g e s t i n g

296

PESTICIDE

CHEMISTRY

I N T H E 20TH

CENTURY

t h a t t h e a c t i o n o f t h e hormone i s n o t on i n d u c t i o n p e r s e , b u t r a t h e r on the v e g e t a t i v e phase w h i c h p r e c e d e s i t ( 1 2 ) : ( T ) . I f g i b b e r e l l i n s produced i n seeds a r e the main cause of f l o w e r i n h i b i t i o n and hence o f b i e n n i a l b e a r i n g i n f r u i t t r e e s , we m i g h t e x p e c t t o f i n d d i f f e r e n c e s i n g i b b e r e l l i n p r o d u c t i o n b e t w e e n s t r o n g l y b i e n n i a l a n d more r e g u l a r c r o p p i n g v a r i e t i e s . In f a c t , although v a r i e t i e s d i f f e r i n their g i b b e r e l l i n prod u c t i o n , no c o r r e l a t i o n w i t h b i e n n i a l c r o p p i n g t e n d e n c i e s exists (10). A n a l t e r n a t i v e a n d more l i k e l y e x p l a n a t i o n i s s u g g e s t e d b y t h e w o r k o f G . V . Hoad a t L o n g A s h t o n (13) > w h i c h shows t h a t i n t h e s t r o n g l y b i e n n i a l L a x t o n s S u p e r b a much l a r g e r q u a n t i t y o f g i b b e r e l l i n c a n be c o l l e c t e d i n a n a g a r b l o c k p l a c e d o n t h e c u t b a s e o f t h e p e d i c e l t h a n i n t h e l e s s b i e n n i a l C o x ' s Orange P i p p i n , suggesting that g i b b e r e l l i n transport i s a key f a c t o r i n biennial cropping.

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch016

!

Chemical c o n t r o l of b i e n n i a l f l o w e r i n g . On t h e b a s i s o f t h e s e h y p o t h e s e s we c a n s u g g e s t s e v e n p o s s i b l e ways i n w h i c h g r o w t h r e g u l a t o r s m i g h t be u s e d t o c o n t r o l b i e n n i a l f l o w e r i n g and c r o p p i n g . . F o u r o f t h e s e a r e t r e a t m e n t s w h i c h c o u l d be a p p l i e d i n the ' o n ( f r u i t i n g ) year to i n c r e a s e flower i n d u c t i o n , and t h r e e a r e d e s i g n e d t o d e c r e a s e f l o w e r i n d u c t i o n and w o u l d t h e r e f o r e be a p p l i e d i n t h e ' o f f ( n o n - f r u i t i n g ) y e a r . To i n c r e a s e f l o w e r i n g we m i g h t : 1

1 . B l o c k GA s y n t h e s i s . T h e r e a r e a number o f a n t i g i b b e r e l ï i n c ô m p ô u n d s ~ " w h i c h p r o b a b l y f u n c t i o n i n t h i s w a y . On a p p l e s t h e most e f f e c t i v e i s s u c c i n i c a c i d - 2 , 2 - d i m e t h y l h y d r a z i d e ( d a m i n o z i d e , SADH, ' A l a r ' ) . T h i s compound i s w i d e l y u s e d f o r i n d u c i n g e a r l y c r o p p i n g , a n e x t r e m e example o f w h i c h i s t h e 'meadow o r c h a r d ' , a n e x p e r i m e n t a l s y s t e m o f a p p l e p r o d u c t i o n i n which t r e e s , planted 1 2 x 1 8 inches apart are sprayed w i t h daminozide to induce f l o w e r i n i t i a t i o n i n t h e i r f i r s t year of g r o w t h (H) · The e f f e c t o f d a m i n o z i d e o n f l o w e r i n d u c t i o n ( T a b l e iYJ c a n be e n h a n c e d b y m i x i n g i t w i t h 2 - c h l o r o e t h y l TABLE

II

A d d i t i v e e f f e c t s o f daminozide and ethephon on the i n d u c t i o n o f f l o w e r s o n o n e - y e a r - o l d t r e e s o f a p p l e c v . C o x ' s Orange P i p p i n . Mean number o f b l o s s o m c l u s t e r s / t r e e a s a r e s u l t o f a s i n g l e s p r a y a p p l i e d t h e p r e v i o u s summer Ethephon (ppm)

0

D a m i n o z i d e (ppm) 625 1250

2500

0

3

8

10

12

625 1250 2500

9 10 16

11 12 19

13

17 22 21

15 23

16.

LucKwiLL

Flowering

and

Fruit

297

Development

phosphonic a c i d (ethephon). While i t i s most e f f e c t i v e on nonf r u i t i n g t r e e s , daminozide w i l l a l s o i n c r e a s e flower i n d u c t i o n on f r u i t i n g t r e e s , "but where the crop i s very heavy, as i t o f t e n i s i n 'on years of s t r o n g l y b i e n n i a l v a r i e t i e s , i t s e f f e c t i s q u i t e small. I t i s t h e r e f o r e not very u s e f u l f o r the c o n t r o l of biennialism. 1

2. Block GA_transport. A number of growth r e g u l a t o r s are known which w i l l block~the t r a n s p o r t of g i b b e r e l l i n from seed to bourse, and compounds such as 2,3,5-tri-iodobenzoic a c i d are e f f e c t i v e i n p e r m i t t i n g flower i n d u c t i o n to take place even i n the presence of a heavy crop. But the flowers so induced set p o o r l y and no increase i n crop i s obtained, probably because the food reserves of the tree have been depleted (Table I I I ) . So again, t h i s i s not a p r a c t i c a l method. Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch016

(TIBA)

TABLE I I I E f f e c t of TIBA 150 ppm a p p l i e d as a spray to heavy cropping t r e e s of apple cv. George Cave i n 1969 Control

TIBA

Blossom c l u s t e r s per t r e e i n 1970

253

611

Crop per t r e e

27.6

(kg)

35.4

Significance

S i g n i f i c a n t at < Not

1.0$

significant

3. Induce seedless f r u i t . As we have seen, seedless f r u i t s do not i n h i b i t flower i n i t i a t i o n . In many v a r i e t i e s of apple and pear seedless f r u i t s can be induced by a p p l y i n g growth r e g u l a t o r s under c o n d i t i o n s where n a t u r a l p o l l i n a t i o n has f a i l e d or been prevented. But the most e f f e c t i v e growth r e g u l a t o r i s GA, p a r t i c u l a r l y when mixed with the r i g h t p r o p o r t i o n of an auxin, such as 2-naphthoxyacetic a c i d (2-NOA) and a c y t o k i n i n . Hence, the treatment which induces parthenocarpy i s i t s e l f i n h i b i t o r y to flower i n d u c t i o n . 4· Thin f r u i t l e t s . This i s the most p r a c t i c a l and widely used 'on' year""treatment to even out cropping from year to year. Naphthalene compounds, p a r t i c u l a r l y 1-naphthylacetic a c i d (NAZI) and i t s amide (NAm) and the i n s e c t i c i d e c a r b a r y l (1-naphthyl methyl^carbamate) have been widely used f o r many years to induce the a b s c i s s i o n of f r u i t l e t s : but timing i s c r i t i c a l and e f f e c t s can vary widely from season to season depending, amongst other f a c t o r s , on r a t e of uptake and metabolism. Recently there has been much i n t e r e s t i n the p o s s i b i l i t y of u s i n g ethephon f o r f r u i t t h i n n i n g but, here again, a t t e n t i o n to time of a p p l i c a t i o n i s r e q u i r e d to a v o i d complete d e - f r u i t i n g of the t r e e as f r u i t l e t s abscind much more r e a d i l y i n June, when n a t u r a l auxin production i s low, than i n May or J u l y (Table IV").

PESTICIDE C H E M I S T R Y IN T H E 2 0 T H C E N T U R Y

298

TABLE I V The v a r y i n g s e n s i t i v i t y o f a p p l e c v . C o x s Orange P i p p i n t o ethephon a p p l i e d a t d i f f e r e n t times as a f r u i t t h i n n i n g a g e n t . io f r u i t d r o p d u r i n g t h e 11 d a y s f o l l o w i n g s p r a y i n g 1

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch016

Ethephon cone,

May June July August September

(ppm)

0

200

1000

2.5 11.5 2.5 2.7 5.0

2.8

32.0 15.0 10.0

41.5 92.5 15.0 46.0 49.5

' O f f y e a r t r e a t m e n t s w h i c h have decrease flower i n i t i a t i o n i n c l u d e : -

12.8

been t r i e d

i n order

to

5. Reduce l e a f _ a r e a . A p p l i c a t i o n o f 1$ NaDNOC e a r l y i n t h e s e a s o n t o s c o r c h t h e y o u n g f o l i a g e i s a p o s s i b l e way o f r e d u c i n g flower induction; h o w e v e r , a n u n a c c e p t a b l e amount o f l e a f damage must be i n f l i c t e d t o g e t a w o r t h - w h i l e r e d u c t i o n i n b l o o m the f o l l o w i n g y e a r , and t h i s l e a f a r e a i s needed to b u i l d up the f o o d r e s e r v e s of the t r e e . 6. A p p l y G A . A n a t t r a c t i v e p o s s i b i l i t y i s t o s p r a y t h e t r e e w i t h GA i n t h e ' o f f year to prevent e x c e s s i v e f l o w e r i n i t i a t i o n , p a r t i c u l a r l y as t h i s does not a f f e c t the photosynthetic e f f i c i e n c y of the f o l i a g e . U n f o r t u n a t e l y , even at h i g h c o n ­ centrations, GA h a s p r o v e d i n e f f e c t i v e on c o m p l e t e l y ' o f f year o r d e b l o s s o m e d t r e e s , a l t h o u g h i t w i l l i n h i b i t f l o w e r i n g when a p p l i e d to f r u i t i n g t r e e s . The e x p l a n a t i o n o f t h i s p a r a d o x i s n o t c l e a r b u t i t may be t h a t t h e g i b b e r e l l i n h a s t o combine w i t h some s e c o n d f a c t o r f r o m t h e f r u i t i t s e l f b e f o r e i t c a n become i n h i b i t o r y t o f l o w e r i n d u c t i o n (15)· 1

1

7* A p p l y o t h e r _ f l o w e r _ i n h i b i t o r s . Besides g i b b e r e l l i n , a number o f o t h e r compounds a r e ~ k n o w n w h i c h w i l l r e d u c e f r u i t b u d formation i n apple. T h e y i n c l u d e m e t a - t ο l y l p h t h a l a m i c a c i d and x a n t h i n e (1 θ ) and t h e h e r b i c i d e s b r o m o u r a c i l a n d t h i o u r a c i l u s e d i n low (50 ppm) c o n c e n t r a t i o n (16), b u t none o f t h e s e h a v e y e t found commercial a p p l i c a t i o n . To sum up - i t w o u l d seem t h a t r e d u c t i o n o f t h e o n y e a r ' crop by b l o s s o m o r f r u i t t h i n n i n g w i t h growth r e g u l a t o r s remains t h e most p r a c t i c a l way o f c o n t r o l l i n g b i e n n i a l b e a r i n g i n a p p l e s : b u t we s t i l l n e e d more r e l i a b l e a n d c o n s i s t e n t f r u i t t h i n n i n g agents. !

16.

LucKwiLL

Flowering

and Fruit

Development

299

F r u i t Development

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch016

1

'Direct a c t i o n hypothesis. In the w i l d , the f r u i t i s simply the packaging f o r the a l l - i m p o r t a n t seeds on which the f u t u r e of the species depends, so i t i s not s u r p r i s i n g i n c u l t i v a t e d f r u i t s to f i n d that seed and f r u i t development are c l o s e l y l i n k e d . Although amongst c u l t i v a t e d f r u i t s there are notable exceptions, the general r u l e i s - no seed development, no f r u i t . Moreover, the number and d i s p o s i t i o n of seeds i n the f r u i t determine i t s s i z e and shape, i t s l i a b i l i t y to drop before i t i s f u l l y grown and o f t e n i t s biochemistry and storage prop e r t i e s . These f a c t s have long been known. L a t e r i t was d i s covered that by a p p l y i n g growth r e g u l a t o r s of the auxin or g i b b e r e l l i n type, seedless f r u i t s of many species could be induced to develop without the usual p r e l i m i n a r i e s of p o l l i n a t i o n and f e r t i l i z a t i o n . The next discovery was that developing (though not mature) seeds were themselves r i c h sources of hormones such as c y t o k i n i n s , auxins and g i b b e r e l l i n s . These hormones are produced i n the seed, not at a steady r a t e , but i n strong f l u s h e s i n w e l l marked succession corresponding with the development of successive t i s s u e s w i t h i n the seed - f i r s t the n u c e l l u s , then the f r e e nuclear endosperm, the c e l l u l a r endosperm and f i n a l l y the embryo i t s e l f . At t h i s point i t seemed reasonable to propose the hypothesis that the f r u i t t i s s u e s grew i n d i r e c t response to hormonal s t i m u l i emanating from the seeds. In p a r t i c u l a r , i t seemed l o g i c a l to assume that c y t o k i n i n s , i n which the f r e e - n u c l e a r endosperm i s r i c h , were a s s o c i a t e d with the e a r l y phases of f r u i t growth i n which c e l l d i v i s i o n i s dominant, w h i l s t g i b b e r e l l i n s , which appear l a t e r , were r e s p o n s i b l e f o r s t i m u l a t i n g c e l l enlargement. Unfortunately, t h i s simple hypothesis was not s u b s t a n t i a t e d by more d e t a i l e d i n v e s t i g a t i o n s which, with few exceptions, showed no c l o s e c o r r e l a t i o n between the peaks of hormone production i n the seed and the v a r i o u s phases of f r u i t growth. In the apple, f o r i n s t a n c e , there i s no apparent c o r r e l a t i o n between the percentage i n c r e a s e i n volume of the f r u i t each week and the c o n c e n t r a t i o n of g i b b e r e l l i n i n the seeds ( F i g . 2 ) . 'Competing s i n k s ' hypothesis. Although a few adherents of the ' d i r e c t a c t i o n hypothesis' ( i n c l u d i n g most text books'.) s t i l l f i g h t a rearguard a c t i o n , most workers i n t h i s f i e l d have now t r a n s f e r r e d t h e i r a l l e g i a n c e to the hypothesis of 'competing s i n k s ' . This supposes that the f a c t o r normally l i m i t i n g the growth of an ovary i n t o a f r u i t i s not the minute q u a n t i t i e s of hormone r e q u i r e d f o r c e l l d i v i s i o n and c e l l expansion, but r a t h e r the carbohydrates and amino a c i d s needed f o r b u i l d i n g new t i s s u e s which are r e q u i r e d i n l a r g e q u a n t i t i e s . These have to be a t t r a c t e d from the general pool against the competing demands of the v e g e t a t i v e growing p o i n t s . Although the mechanism i s obscure there i s strong evidence that metabolites and mineral elements

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch016

300

PESTICIDE C H E M I S T R Y IN T H E 2 0 T H C E N T U R Y

c Figure 1. Hormonal factors influencing flower initiation in bourse bud of apple. G = gibberel­ lins, C = cytokinins, F = florigin ?

9

Γ

0

5

10

Weeks a f t e r

15

20

full-bloom

Figure 2. Gibberellin production in seeds of apple com­ pared with rate of increase in fruit volume (cv. Cox s Orange Pippin)

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch016

16.

LucKwiLL

Flowering

and

Fruit

Development

301

move p r e f e r e n t i a l l y t o w a r d s i t e s o f h i g h hormone c o n c e n t r a t i o n . Of t h e t h r e e m a j o r g r o u p s o f g r o w t h p r o m o t e r s a u x i n s a r e o f prime importance i n s t i m u l a t i n g t h i s h o r m o n e - d i r e c t e d t r a n s p o r t , but combination w i t h g i b b e r e l l i n s or c y t o k i n i n s , or b o t h , r e s u l t s i n strong s y n e r g i s t i c a c t i o n (17)· On t h i s h y p o t h e s i s t h e h i g h c o n c e n t r a t i o n s o f hormones f o u n d i n t h e s e e d s a r e n e c e s s a r y i n order to create a s t r o n g p h y s i o l o g i c a l s i n k capable of competing w i t h the stem and r o o t a p i c e s . The m a i n e x p e r i m e n t a l e v i d e n c e f o r t h i s h y p o t h e s i s comes f r o m e x p e r i m e n t s i n w h i c h t h e c o m p e t i t i o n between v e g e t a t i v e and f r u i t growth i s p a r t i a l l y r e l i e v e d by r e m o v i n g a l l the shoot t i p s q u i t e e a r l y i n t h e season. I f the s u p p r e s s i o n of shoot growth i s v e r y severe i t i s p o s s i b l e to induce p a r t h e n o c a r p i c or s e e d l e s s development of t h e f r u i t b y t h i s method ( 1 8 ) . In other s i t u a t i o n s f r u i t set c a n be g r e a t l y e n h a n c e d t h r o u g h a n i n c r e a s e d r e t e n t i o n o f f r u i t l e t s w h i c h o t h e r w i s e would have dropped o f f because t h e i r s e e d c o n t e n t was t o o low t o e n a b l e them t o c o m p e t e . The d a t a o f Q u i n l a n a n d P r e s t o n (j_9) c o n f i r m t h e e a r l i e r f i n d i n g s o f A b b o t t a n d s u g g e s t t h a t we h a v e h e r e a p o t e n t i a l l y v a l u a b l e t e c h n i q u e f o r i m p r o v i n g the c r o p p i n g o f a p p l e s at t h e expense o f shoot g r o w t h , much o f w h i c h i s n o t r e q u i r e d a n d w i l l , i n a n y e v e n t , be removed i n w i n t e r p r u n i n g . But manual removal o f shoot t i p s i s h a r d l y p r a c t i c a l on a n o r c h a r d s c a l e ; what we n e e d i s a g r o w t h r e g u l a t o r which w i l l a r r e s t shoot growth without c a u s i n g u n d e s i r a b l e s i d e e f f e c t s on the f r u i t . Daminozide has p r o v e d q u i t e e f f e c t i v e on y o u n g t r e e s , when a p p l i e d s h o r t l y a f t e r p e t a l f a l l a n d i s now u s e d as a r o u t i n e s p r a y i n t h e 'meadow o r c h a r d to increase f r u i t set (Table V ) . Dramatic i n c r e a s e s i n y i e l d are 1

TABLE V P r o m o t i o n of f r u i t - s e t i n a p p l e by s u p p r e s s i n g shoot growth w i t h d a m i n o z i d e 2500 ppm a p p l i e d a t p e t a l - f a l l s t a g e . Mean o f 100 t r e e s

Variety L o r d Lambourne Egremont R u s s e t

F r u i t s p e r 100 Control

10 17

blossom c l u s t e r s Daminozide

23 58

o b t a i n e d on t h e s e s m a l l t r e e s , b u t t h e method i s n o t so e f f e c t i v e on t h e more c o n v e n t i o n a l t y p e o f t r e e . Other growth r e g u l a t o r s w h i c h have been t e s t e d i n c l u d e ( 2 - c h l o r o e t h y l ) trimethylammonium c h l o r i d e (CCC, Chlormequat, C y c o c e l ) , A n c y m i d o l , m a l e i c h y d r a z i d e , m o r p h a c t i n s and f a t t y a c i d e s t e r s , b u t a l l produce u n d e s i r a b l e s i d e e f f e c t s on l e a f o r f r u i t g r o w t h o r s k i n f i n i s h : n e v e r t h e l e s s t h e p r i n c i p l e i s e s t a b l i s h e d as a s o u n d one - a l l

302

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch016

we n e e d i s

PESTICIDE C H E M I S T R Y IN T H E 2 0 T H C E N T U R Y

the

right

growth

regulator'.

I n d u c t i o n of parthenocarpy. A n a l t e r n a t i v e method o f i m p r o v i n g f r u i t s e t , or of c o m p l e t e l y c i r c u m v e n t i n g the need f o r p o l l i n a t i o n , i s b y hormone s p r a y i n g t o i n d u c e p a r t h e n o c a r p y , a method w h i c h h a s f o u n d c o m m e r c i a l a p p l i c a t i o n i n t h e p r o d u c t i o n o f s e e d l e s s g r a p e s , i n f i g s and t o m a t o e s , and a l s o i n p e a r s , where GA s p r a y s h a v e b e e n u s e d t o s a v e t h e c r o p a f t e r t h e f l o w e r s o r f r u i t l e t s h a v e b e e n damaged b y s p r i n g f r o s t s ( 2 0 ) . In species w h i c h r e s p o n d t o hormone s p r a y s i t i s o f t e n f o u n d t h a t s y n t h e t i c a u x i n s , g i b b e r e l l i n s and sometimes c y t o k i n i n s , a r e e q u a l l y e f f e c t i v e i n s t i m u l a t i n g f r u i t growth, and t h a t the t h r e e d i f f e r e n t t y p e s o f h o r m o n e s , when a p p l i e d i n m i x t u r e s , show s y n e r g i s t i c a c t i v i t y , an o b s e r v a t i o n which suggests t h a t the mechanism o f a c t i o n i s s i m i l a r t o t h a t s u g g e s t e d f o r the endogenous hormones, v i z . c r e a t i n g m o b i l i z a t i o n c e n t r e s f o r m e t a b o l i t e s r a t h e r than d i r e c t s t i m u l a t i o n of t i s s u e growth. The a p p l e h a s p r o v e d one o f t h e most d i f f i c u l t s u b j e c t s f o r t h e c h e m i c a l i n d u c t i o n o f p a r t h e n o c a r p y , and f o r t h i s r e a s o n the work o f Schwabe a n d h i s c o - w o r k e r s a t Wye C o l l e g e i n E n g l a n d i s o f g r e a t i n t e r e s t and p o t e n t i a l v a l u e to the f r u i t i n d u s t r y . They h a v e d e v e l o p e d a t r i p l e hormone f r u i t - s e t t i n g s p r a y c o n t a i n i n g g i b b e r e l l i c a c i d (600 p p m ) , t h e s y n t h e t i c a u x i n 2-naphthoxyacetic a c i d (40 ppm) a n d t h e c y t o k i n i n b e n z y l a d e n i n e (300 ppm) - more r e c e n t l y r e p l a c e d by d i p h e n y l u r e a (21). T r i a l s o n C o x ' s Orange P i p p i n o v e r e i g h t y e a r s have g i v e n c o n s i s t e n t i n c r e a s e s i n y i e l d on b o t h p o l l i n a t e d a n d u n p o l l i n a t e d f l o w e r s . On sweet c h e r r y (cvs E a r l y R i v e r s and M e r t o n G l o r y ) v e r y s p e c t a c u l a r yield i n c r e a s e s h a v e b e e n a c h i e v e d a n d t h e same m i x t u r e h a s g i v e n p r o m i s i n g r e s u l t s on E u r o p e a n plum ( c v . V i c t o r i a ) . Apart from t h e p o s s i b l e s i d e e f f e c t s o f t h i s s p r a y on f l o w e r p r o d u c t i o n f o r the f o l l o w i n g y e a r , the h i g h c o s t of g i b b e r e l l i c a c i d would p r o b a b l y make t h e t r e a t m e n t u n e c o n o m i c a t t h e p r e s e n t t i m e . C o n t r o l of f r u i t r i p e n i n g and a b s c i s s i o n . The r i p e n i n g o f f r u i t s s u c h as t h e a p p l e w h i c h show a r e s p i r a t i o n c l i m a c t e r i c h a s l o n g b e e n known t o be a s s o c i a t e d w i t h e t h y l e n e , and t h e a d v e n t o f compounds s u c h as e t h e p h o n , w h i c h r e l e a s e e t h y l e n e w i t h i n the t i s s u e s o f the p l a n t , has g i v e n us an u n p r e c e d e n t e d degree o f c o n t r o l over the r i p e n i n g p r o c e s s . It enables f r u i t growers to h a r v e s t h i g h q u a l i t y apples e a r l i e r i n the season t h a n w o u l d o t h e r w i s e be p o s s i b l e a n d t o s p r e a d t h e i r l a b o u r requirements f o r h a r v e s t over a l o n g e r p e r i o d than would o t h e r w i s e be p o s s i b l e . Ethephon a l o n e w i l l i n d u c e a b s c i s s i o n and t o c o u n t e r a c t t h i s i t n e e d s t o be a p p l i e d i n c o m b i n a t i o n w i t h a n a u x i n , s u c h as 2 , 4 , 5 - T P , or w i t h daminozide. A combination of 750 ppm a . i . e t h e p h o n a n d 15 ppm 2 , 4 , 5 - T P a p p l i e d a b o u t 10 d a y s b e f o r e t h e d e s i r e d h a r v e s t d a t e h a s p r o v e d h i g h l y e f f e c t i v e on e a r l y v a r i e t i e s s u c h as W o r c e s t e r P e a r m a i n ( T a b l e V I ) a n d E a r l y

16.

LUCKwiLL

Flowering

and

Fruit

303

Development

M a c i n t o s h , w h e r e a s m a i n c r o p v a r i e t i e s t e n d t o r e a c t more s l o w l y . The r a t e o f r e a c t i o n i s a f u n c t i o n , n o t o n l y o f v a r i e t y , b u t a l s o of temperature and degree of water s t r e s s a n d , i n p r a c t i c e , TABLE V I Effect the

of ethephon i n combination w i t h daminozide or 2 , 4 , 5 - T P

q u a l i t y of Worcester

Pearmain apples h a r v e s t e d

Control

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch016

% of f r u i t s •4 o r more Relative

1-6

amount

content

colour

(on

resistance

fo p r e - h a r v e s t

0

68

60

170

270

220

of

a

scale)

Pressure

Ethephon + 2,4,5-TP

with

surface

anthocyanin Starch

Ethephon + daminozide

on

on A u g . 2 5 t h

drop

(lb)

1.4

1.9

4.4

18.7

18.7

17.0

8.3

1.6

8.6

g r o w e r s a r e recommended t o f o l l o w t h e p r o g r e s s o f r i p e n i n g b y a simple starch/iodine t e s t (22). O t h e r compounds, s u c h as b e n z y l - i s o t h i o c y a n a t e (23)> a c t a s a n t i e t h y l e n e .agents - p r o b a b l y by b l o c k i n g n a t u r a l b i o s y n t h e s i s a n d t h e s e may f i n d a p p l i c a t i o n s f o r d e l a y i n g r i p e n i n g o f f r u i t s and perhaps p r o l o n g i n g t h e i r s t o r a g e l i f e . Conclusions G r o w t h r e g u l a t o r s c l e a r l y have many u s e s a n d p o t e n t i a l u s e s i n f r u i t growing. A l t h o u g h I h a v e c o n c e n t r a t e d on t h e a p p l e , o n w h i c h most w o r k h a s b e e n d o n e , a s i m i l a r s t o r y c o u l d h a v e b e e n t o l d f o r a l m o s t any o t h e r c u l t i v a t e d f r u i t i n w h i c h growth r e g u l a t o r s c a n m o d i f y c r o p p i n g b e h a v i o u r t h r o u g h e f f e c t s on f l o w e r i n d u c t i o n and f r u i t s e t . I h a v e s t r e s s e d how l o c a l c o n c e n t r a t i o n s o f e n d o g e n o u s h o r m o n e s , s u c h as o c c u r i n s h o o t t i p s and young s e e d s , r e g u l a t e the d i s t r i b u t i o n of p h o t o s y n t h a t e s by c r e a t i n g p h y s i o l o g i c a l ' s i n k s ' , the r e l a t i v e s t r e n g t h s of which determine the p r o p o r t i o n of the t r e e ' s r e s o u r c e s which i t d e v o t e s t o f r u i t p r o d u c t i o n as o p p o s e d t o v e g e t a t i v e g r o w t h , much o f w h i c h i s u n w a n t e d a n d i s d e s t i n e d t o be p r u n e d away t h e following winter. Some p r o g r e s s t o w a r d t h e c o n t r o l o f a s s i m i l a t e p a r t i t i o n i n g b y means o f g r o w t h r e g u l a t o r s h a s b e e n made, a n d one p r a c t i c a l outcome i s t h e n o v e l s y s t e m o f a p p l e p r o d u c t i o n known as t h e

304

PESTICIDE C H E M I S T R Y IN T H E 2 0 T H C E N T U R Y

'meadow orchard'. I t i s probably i n this f i e l d of assimilate partitioning that the greatest potential for the future use of growth regulators l i e s . Literature Cited 1. 2. 3.

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch016

4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21.

53,

22. 23.

Chailakhyan, M. Kh. Fiziologiya Rast. (1971) 18(2), 348-557. Luckwill, L.C. and Whyte, P. S.C.I. Monogr. (1968) No.31, 87-101. Beever, J . E . and Woolhouse, H.W. Nature (New Biology) Lond. (1973) 246, 31-32. Mullins, M.G. J. exp. Bot. (1967) 18, 206-214. Skene, K.G.M. Science (1968) 159, 1477-1478. Monselise, S.P. and Halevy, A.H. Proc. Amer. Soc. hort. Sci. (1964) 84, 141-146. Huet, J. Physiologie V é g é t a l e (1972) 10(3), 529-545. Tumanov, I.I. and Gareev, E.Z. Trudy. Inst. Fiziol. Rast. Timirjazeva 7, 22-108. Chan, B.G. and Cain, J . C . Proc. Amer. Soc. hort. S c i . (1967) 91, 63-67. Luckwill, L . C . "Physiology of Tree Crops" 237-253. Academic Press, London and New York (1970). Luckwill, L . C . , Weaver, P. and MacMillan, J . J. hort. S c i . (1969) 44, 413-424. Luckwill, L . C . Proc. XIX Int. Hort. Congr. Warsaw (1975) III, 235-245. Hoad, G.V. Rep. Long Ashton Res. Stn for 1975 (1976) 43. Luckwill, L . C . and Child, R.D. Acta Horticulturae (1973) 34(1), 213-220. Fulford, R.M. Rep. East Mailing Res. Stn for 1972 (1973) 93. Buban, T. Bot. K ö z l . (1969) 56(4), 251-256. Seth, A.K. and Wareing, P.F. J. Exp. Bot. (1967) 18, 65-77. Abbott, D.L. Ann. appl. Biol. (1960) 48, 434-438. Quinlan, J.D. and Preston, A . P . J. hort. S c i . (1971) 46 525-534. Luckwill, L . C . Rep. Long Ashton Res. Stn for 1961 (1962) 61-66. Goldwin, G.K. and Schwabe, W.W. Proc. 12th British Weed Control Conf. (1974) 131-136. Luckwill, L.C. and Child, R.D. Expl Hort. (1973) 25, 1-6. P a t i l , S.S. and Tang, Chung-Shin, Plant Physiol. (1974) 585-588.

INDEX

Β

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ix001

A aaaeee Aabomycin A Abscission, control of

15 185 302

Acanthoscelides obtectus

216

ACD 15M Acylanilides

86 56, 62 27

Aedes nigromaculis

Agricultural antibiotics Alachlor Alarm pheromones Aldrin 2-Alkanones

170 48 224 5 224

Altosid Amchem Ametryn Animals, toxicity of antibiotics to

27 46 84 185

Alternaria kikuchiana

Anopheles albimanus

Ansul

Anthonomus

grandis

164

27

46

217

Antibiotic ( s ) agricultural 170 antifungal 172 antiviral 184 herbicidal 184 toxicity to animals 185 Anticholinesterase insecticides 8 Antidifferentiation compounds 121 Antifungal activity of ethyltin compounds 132 activity of triorganotin acetates 133 antibiotics 172 Anti-herbicides 54 Antimicrobal actvity of organometallic compounds 131 Antiviral antibiotics 184 Apple(s) 240,280,289,290 Argyotaenia velutinana Aristapedia

Atratone Atrazine

Attagenus megatoma ..:

Auxin(s) Avocado(s) Azido-s-triazines Aziprotryn Azobenzene

211 30

83 46, 83, 88 217

285,289,299 280,282 63 87 25

Bark beetle 210 Barley 262 BASF 48 BASF 54187 85 BAY 138,992 68 Bayer 8 Bender, Harry 2 Benezene hexachloride 1 Benomyl 163 Bentazon 48 Benzimidazole ( s ) 63,166 Benzodioxole derivatives 9 Benzonitriles, halogenated 56 Benzoylphenyl ureas 237 Benzylic deuteration of D D T 9 Benzylic hydroxylation of D D T 9 Biennial flowering, chemical control of 296 Biosynthesis of juvenile hormones .... 203 Bipyridiliums 56 Birdsfoot trefoil 88 Blasticidin S 170,172 Blastin 118,121 Block GA synthesis 296 Block GA transport 297 Boll weevil 217 Bombykol 209 Boophilus 27 Bordeaux mixture 157 Br-DDT 8 Brestan 163 Bromacil 46 82

216

Bruchidae

Buntin, G. A Burrage

7 2

C C. erythrocephah

California red scale Camphene Captan Carbamate(s) anticholinesterases resistance Carbaryl Carboxin

305

17

21, 22 7 16° 24 8 25, 26 26 119

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ix001

306

PESTICIDE C H E M I S T R Y I N T H E 2 0 T H

Carboxyesterase

25

Carmine

30

CENTURY

D

44 Carotenoid synthesis 56 153 Carpet beetles 217 44 Cattle ticks 27 289,302 Cecrophia moth 198 13 Cellocidin 181 3,13 Chemosterilants 27 9 Chemotherapy 117 9 Chiral world of insects 228 22, 26 Chitin 264 97 Chitin deposition 237 Deh 30 Chloramben 46 Dehydrochlorination 5 Chloranil 118 Dermestidae 217 Chlordane 5 Derris substitutes 2 Chlordene 5 Desmetryn 84 Chlordimeform 27 Dexon 118 Chlorinated insecticides 1, 11 Dialkyllead compounds 142 p-Chloroaniline 251 Dialkyltin compounds 142 p-Chlorophenyl urea 251 Diazotization 98 Chloroplast(s) 57 Dichlobenil 237 Chloroplast-mediated reactions 57 3,4-Dichlorbenzene 3 Chlorotriazines 87 Dichlorovinyl pyrethroid NRDC-143 27 Chlor-phenamidine 27 Dictyoptera 212 Chlorpyrifos 27 Dieldrin 5 Cholinesterase 22 Dienophile 5 Chrysanthemic acid 25 Diflubenzuron 32, 240, 241 CIBA 48 Diflubenzuron in the environment 246 Cockroach ( es ) 206, 213, 265,273 Difolatan 160,164 Codling-moth larvae 21 Dihalogenated benzonitriles 62, 63 Coleptera 216 Dimethametryn 85 Corn borer, European 211 Dimethoate 28 Costelytra zealanaica 216 Dimethyl-dithiocarbamates 125 Costs Dimilin 27, 32 fertilizer 42 Dinitroanilines 56 grain drying 42 Dipropetryn 84 irrigation 42 Diptera 215 storage 43 Disarming pheromones 226 transportation 43 Diuron 44 Cotton 240 Dow Chemical 44 Cotton leafworm 25 Drosophila 28, 30 Crab grass 88 DSMA 46 Culex pipiens 31 Dupire 2 Culex quinquefasciatus 31 du Pont 44 Culex tarsalis Curculionidae

Cyameluric chloride Cyanatrine Cyanazine Cyclodiene(s) insecticides photochemistry of resistance Cycloheximide Cyprazine Cytochrome f Cytochrome oxidase Cytochrome P450 Cytokinin ( s )

2,4-D Daines, Robert H Dalapon Daminozide DANP DDT benzylic deuteration of benzylic hydroxylation of resistance Degradation of herbicides

31 217

80 86 86, 87 3 11 23 170 85 60 22 9,10 284, 285, 290, 299

Ε EC α-Ecdysone Elateridae

Electron acceptors Electron-capture Electron transport inhibitors Endosulfan Endrin Energy transfer inhibitors Environmental chemistry of herbicides EPTC

10 199 216

60, 62 10 50, 60 7 5 60, 61 93 44

INDEX

307

Ethephon 105,289,302, 303 Ethrel 105 Ethylene hormonal interactions with 284 physiological responses to 280 as a ripening agent, resistance to .... 282 Ethyltin compounds, antifungal activity of 132 Eulan BL 3 European corn borer 211 Exocrinological chemistry, evolution of 209 Ezomycins 181

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ix001

F Face flies Faraday, Michael Farbenindustrie, I.G Fenthion Ferredoxin Fertilizer costs Flight initiation pheromones Flower induction, leaves promote induction, seeds inhibit initiation Fluometuron Fly Formamidines Free radical mechanisms Frensch, Heinz Fruit development ripening, control of seedless Fruitlets, thin Fungicidal applications of tributyltin Fungicides, metallo-organic

215 1 3 27 60 42 227 294 295 293 48 240 25 72 7 299 302 297 297 146 123

H

Heliothis caterpillars

24

Heliothis virescens Hemiptera

Herbicidal antibiotic Herbicide(s) classification of inhibitory degradation of environmental chemistry of future developments industry postemergence preemergence toxicity of common s-triazine Heterocyclic inhibitors hex Hexachloronorbornadiene Hexachloronorbornene Hexachlorocyclopentadiene Hill inhibitors Hill reaction Hoechst Holan

25,30 214

184

60 97 93 54 39 50 50 102 76 65 3 5 11 3 60 56,60, 62 46 13 214

Homoptera

Hormonal control of insect development 197 Hormonal interactions with ethylene 284 Hormone(s) analogs as insecticides, juvenile 201 biosynthesis of juvenile 203 isolation 198 House fly 28, 215 27

H. virescens

Hyman, Julius Hymenoptera Hypochlorite

3 223 105 27

H. zea

I

G

Geigy Germanium German cockroach Gibberellins Glyphosphate Grain drying costs Grana Grapes Grass grub beetle Grasshopper Green foxtail Griseochromogenes Griseofulvin GSH

8,46 131 30 285, 296,299 48, 56 42 57 282 216 206 88 172 121,170 24

ICI 46 Imidazoles 63 Indoleacetic acid 57 Induction of parthenocarpy 302 Industry, herbicide 39 Inhibitors electron transport 60 energy transfer 60, 61 heterocyclic 65 hill 60 phenylamide 63 Inhibitory herbicides, classification of 60 Inhibitory uncouplers 60, 62 Insect(s) chiral world of 228 development, hormonal control of .. 197

308

PESTICIDE C H E M I S T R Y IN T H E 2 0 T H C E N T U R Y

Insect(s) (Continued) pheromones, chemistry of 212 toxicology 8 Insecticide ( s ) chlorinated 1,11 cyclodiene 3 juvenile hormone analogs as 201 resistance 21 resistance to the organophosphorus 24 210

Ips paraconfusus

Irrigation costs Isodrin

42 5

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ix001

J

Japanese beetle Juvenile hormone analogs as insecticides

217 201

Κ

Kasugamycin Kearns, C. W Khanenia Kitazin Kittleson, A. F

170,175 5 7 237 153 L

Lambast Langlois Larvicides Lead Leaf roller, oblique-banded Leaves promote flower induction

85 7 237 131 211 294

Lepidoptera

220

Leucophaea maderae

265

Lenzites trabea

Ligands Lilly

Lindane Lindquist Linuron Locust

216

*

Locusta migratoria

2,11,13 22 46 213 213

M

Malaria Malaria mosquito

Manduca sexta md

Mechanical tillage costs Metallo-organic fungicides Metcalf Metham

289 84 184 88 13 127 26 48,68,105 10 30 206 18 22 85 48 31 25 206,240 198 IS 3

Musca autumnalis Musca domestica Musca domestica tiberina

215 215 22

Ν NAA NADH Nakamima Ν Am Naphthalene compounds

297 24 13 297 297

Nasutiteremes exitiosus

212

Norbornadiene N-S bond, nature of

5 156

212

124 ?

Limonius californiens

Methionine Methoprotryn Methoxyphenone Methoxytriazines Methylchlor Methylcobalamin Methyl parathion Metribuzin Microcoulometric detection Microsomal oxidation Milkweed bug Mirex Missiroli MON 0385 Monsanto Monsanto-585 Morestan Mosquitoes Moth, Cecropia Mucoinositol Muller

12 27

199

30 42 123 13 105

Ο

Oblique-banded leafroller OP resistance Orchids Organochlorines sulfur-containing Organometallic compounds, antimicrobal activity of Organophosphorus insecticides, resistance to Organophosphorus resistance Orthoptera

211 24 31 290 27 25 131 24 24,26 213

OSAR

241

Ostrinia nubiïalis Ostrinia obumbratalis

211 211

Oxathiins Oxidative biotransformations in insects Oxythioquinox

166 10 25

INDEX

309 R

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ix001

Ρ Ρτοο 60 Parathion 8,24,27 Paraoxon 24 Paraquat 46 Parthenocarpy, induction of 302 PCB 10 PCMC 105 Pears 164 n-Pentanoic acid 216 Pest control agents, pheromones as .... 229 Phaltan 160 Phenols 56 Phenoxyalkanoic acid herbicides 11 N-Phenylcarbamates 56, 62 Phenylamide inhibitors 63 Phenylureas 56, 62 Pheromone(s) 209 alarm 224 chemistry of insect 212 disarming 226 flight initiation 227 pest control agents 229 sex 225 territorial 226 trail 225 Phosphate anticholinesterase 24 Photochemistry of cyclodienes 11 Physiological responses to ethylene ... 280 Phytotoxicity 70 Phytophthora infestans

Picloram

Pieris hrassicae

Pigment synthesis Piperonyl butoxide Plasto-quinone Plastocyanin Polychlorobiphenyl Polychlorophenols Polycyclic ureas Polyoxin D Polyoxins PopiUa japonica

Postemergence herbicides Precocene-2 Preemergence herbicides Prometone Prometryn Prometryne Propazine Pyrethroids Pryretrin(s) Pyricularia Pyridazinones

Reticulitermes

flavipes

Rhizobitoxine Rice Riemschneider, R Ripening agent, resistance to ethylene as a

217

50 206 50 83 84 105 83, 88 24,25 9,25 172 56

226

117 10 60, 62 57 211 25, 26 26 26 24 212

289,290 170 5 282

S

Sandwich compounds SBD

128 17

Scarabaeidae

216

Scheele, Karl Wilhelm Scolytidae Sebuthylazine Secbumetone Seedless fruit Seeds inhibit flower induction 113 Sencor 46 Sesamex 239, 241 Sex pheromones 72 Silicon 15 57, 60 Silkmoth 60 Silkworm 10 bimazine 11 Simetryn Sitophilus beetles 62 Smartweed borer 265 Soils 121,170,176 Soybeans

Q Queen substance

Rachel Carson syndrome Ray, J. W Reaction, Hill Reactions, chloroplast-mediated Redbanded leaf roller Resistance carbamate DDT organophosphorous to the organophosphorus insecticides

Spodoptera sunia

Stauffer Streptomyces ·. Streptomycin Sugar beet wireworm Sulfone Sulfur-containing organochlorines Sulfene Swedish housefly St/n-chlorine Synthesis, pigment

1 218 83 83 297 295 105 17,22 225 131 198 209 83, 88 84 24 211 246 240 27

44 172 170 216 3 25 80 25 17 72

Τ 2,4,5-T Tanner, C. C

103 2

310 TBTO TCDD Terbumetone Terbuthylazine Terbutryn Termite Territorial pheromones Tetranactin Tetranychid mites

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ix001

Tetranychus mites Tetranychus urticae

PESTICIDE C H E M I S T R Y IN T H E 2 0 T H C E N T U R Y

148 103 83 83 84 212 226 181 24

Triphenyltin acetate Triphenyltin compounds Two-spotted mite U

Uncouplers inhibitory Uracils

28 24,25

Thiolcarbamates 56 Thyalkoids 71 TIBA 297 Tin 30,131 TNO 148 Tobacco budworm 25, 27 Toxaphene 3, 7 Toxicity of antibiotics to animals 185 Toxicity of common herbicides 102 Trail pheromones 225 Transportation costs 43 5-Triazines 56,62 s-Triazine herbicides 76 1,2,4-Triazinones 63 Tribolium 24,27 Tributyltin, fungicidal applications of 146 Trichlorobenzenes 1 Tricyclohexyltin hydroxide 147 Trietazine 83 Trifluralin 48 Triorganotin acetates, antifungal activity 133

133 146 24

60, 61 60,62 56,62 V

Valeric Validamycin Van der Linden Vapam

216 170,178 1 105 113

Venturai inaequalis

Vitavax

163 W

Wild carrot Wilson

,·•·

88 22

X Xenobiotics

12 Ζ

Zeidler Zhuravlev Zoecon

2 7 271