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Chapter 1

Understanding and Combating Agrochemical Resistance A Chemist's Perspective on an Interdisciplinary Challenge

Downloaded by 80.82.77.83 on April 18, 2017 | http://pubs.acs.org Publication Date: February 23, 1990 | doi: 10.1021/bk-1990-0421.ch001

William K. Moberg Agricultural Products Department, E. I. du Pont de Nemours and Company, Stine-Haskell Research Center 300-312C, P.O. Box 30, Newark, DE 19714 Resistance of agricultural pests to chemical control is a problem of growing importance, international scope, and potentially serious consequences. Although resistance-induced crises are not yet the norm, enough have occurred, and with sufficient severity, to make clear the need for action. It is also clear that effective action can only result from interdisciplinary research and cooperation, in which chemists should play an important role. The intent of this chapter is to provide readers, particularly chemists, with background information on the history and current status of pesticide resistance, its genetic basis, and definitions of terms relating to it. Succeeding chapters of this volume support an optimistic view that we are entering an era when most cases of resistance can be managed, provided awareness is followed by a sequence of properly focused fundamental research, communication, consensus building, and proactive implementation of practical measures based on the best scientific information available. R e s i s t a n c e o f a g r i c u l t u r a l p e s t s t o c h e m i c a l c o n t r o l i s now r e c o g n i z e d as one o f t h e most i m p o r t a n t c h a l l e n g e s t o s u s t a i n i n g worldwide p r o d u c t i o n o f f o o d and f i b e r . The amount and q u a l i t y o f f o o d p r o d u c e d t o d a y a r e unique i n r e c o r d e d h i s t o r y , a r i s i n g from l e s s l a n d and l a b o r than e v e r b e f o r e . F o r t h e f i r s t time, man has the a b i l i t y t o e l i m i n a t e hunger i f o n l y t h e b a r r i e r s t o e f f e c t i v e d i s t r i b u t i o n o f f o o d and a g r i c u l t u r a l t e c h n o l o g y c a n be overcome. However, a t l e a s t f o r t h e f o r e s e e a b l e f u t u r e , t h i s abundance cannot be s u s t a i n e d , much l e s s expanded, w i t h o u t t h e c o n t i n u i n g c o n t r i b u tions of agrochemicals. A similar situation exists i n public

0097-6156/90/0421-0001$06.00/0 © 1990 American Chemical Society

Green et al.; Managing Resistance to Agrochemicals ACS Symposium Series; American Chemical Society: Washington, DC, 1990.

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MANAGING RESISTANCE TO

AGROCHEMICALS

h e a l t h , where g o a l s such as m a l a r i a e r a d i c a t i o n , once t a n t a l i z i n g l y c l o s e , are t h r e a t e n e d by i n s e c t i c i d e r e s i s t a n c e . Agrochemicals, and p e s t p o p u l a t i o n s s u s c e p t i b l e t o them, are a c r i t i c a l n a t i o n a l r e s o u r c e f o r d e v e l o p e d and d e v e l o p i n g c o u n t r i e s a l i k e . Objectives

o f the C u r r e n t

Publication


T h i s book a r o s e from the e d i t o r s ' c o n v i c t i o n t h a t r e s i s t a n c e must be managed e f f e c t i v e l y , and t h a t the p r o g r e s s c u r r e n t l y b e i n g made i s b r i n g i n g t h i s g o a l w i t h i n r e a c h i n most c a s e s . I t brings t o g e t h e r e x p e r t s from the t h r e e major a g r o c h e m i c a l a r e a s -i n s e c t i c i d e s , f u n g i c i d e s , and h e r b i c i d e s — w i t h the f o l l o w i n g objectives: •

t o p r o v i d e an update on the c u r r e n t s t a t u s o f r e s i s t a n c e , r e c e n t advances i n u n d e r s t a n d i n g and managing i t , and needs f o r f u t u r e p r o g r e s s ;

•

t o i n t e g r a t e , i n one c o n v e n i e n t s o u r c e , fundamental and a p p l i e d r e s e a r c h , a b r o a d range o f s c i e n t i f i c d i s c i p l i n e s , and a worldwide p e r s p e c t i v e ; and

•

t o i n f o r m c h e m i s t s and o t h e r s c i e n t i s t s , and stimulate their p a r t i c i p a t i o n i n resistance research.

A u t h o r s o f s u c c e e d i n g c h a p t e r s have a d m i r a b l y a c c o m p l i s h e d the f i r s t o b j e c t i v e , d e s c r i b i n g the l a t e s t p r o g r e s s a c r o s s a b r o a d f r o n t o f fundamental s t u d i e s t o u n d e r s t a n d r e s i s t a n c e and p r a c t i c a l measures t o combat i t . I t s h o u l d be n o t e d t h a t two v e r y i m p o r t a n t p a p e r s p r e s e n t e d i n the symposium — Neuropharmacology and M o l e c u l a r G e n e t i c s o f I n s e c t Nerve I n s e n s i t i v i t y t o P y r e t h r o i d s , and G e n e t i c Systems f o r E n g i n e e r i n g P l a n t s f o r R e s i s t a n c e t o Glyphosate — a r e not i n c l u d e d i n the book because o f p u b l i c a t i o n s t h a t were s i m u l t a n e o u s l y i n p r e s s and have now been p u b l i s h e d ( p y r e t h r o i d s , 1,2; g l y p h o s a t e , 1/1). The second and t h i r d o b j e c t i v e s d e s e r v e b r i e f e l a b o r a t i o n . U n t i l now, most d i s c u s s i o n s o f r e s i s t a n c e have t a k e n p l a c e i n b i o l o g i c a l l y oriented s c i e n t i f i c s o c i e t i e s , often with a strong d i s c i p l i n a r y , n a t i o n a l , or r e g i o n a l focus. T h i s can i n s u l a t e the v a r i o u s s c i e n t i f i c d i s c i p l i n e s from e a c h o t h e r , so t h a t l e s s o n s l e a r n e d by one group may not be f u l l y a p p r e c i a t e d or a p p l i e d by others. I t may a l s o have tended t o i s o l a t e c h e m i s t s from r e s i s t a n c e r e s e a r c h , even though t h e y have much t o c o n t r i b u t e . Chemists are an i n t e g r a l p a r t o f new compound d i s c o v e r y , t h e y form a n a t u r a l b r i d g e a c r o s s agronomic and b i o l o g i c a l l i n e s , and t h e y b r i n g a unique s c i e n t i f i c p e r s p e c t i v e t o q u e s t i o n s o f enzyme i n h i b i t i o n , m e t a b o l i s m , and c h e m i c a l t r a n s p o r t i n c r o p s and p e s t s . These are a l l germane t o r e s i s t a n c e r e s e a r c h , y e t most c h e m i s t s c o n c e n t r a t e s o l e l y on u n d e r s t a n d i n g and o p t i m i z i n g a c t i v i t y i n s e n s i t i v e species. And i f t h e y f i n d an i n t e r e s t i n g new compound, t h e y t y p i c a l l y 'throw i t o v e r the w a l l ' t o b i o l o g i s t s , who are e x p e c t e d t o cope w i t h r e s i s t a n c e on t h e i r own. To the e x t e n t t h i s a t t i t u d e


1.

MOBERG

Understanding and Combating Agrochemical Resistance

e x i s t s , i t d e p r i v e s r e s i s t a n c e r e s e a r c h o f a p o t e n t i a l l y important component. We hope t h a t t h i s book c a n p l a y a r o l e i n making c h e m i s t s more a c t i v e p a r t n e r s i n combating r e s i s t a n c e . Overview O b j e c t i v e s Each s e c t i o n o f t h e volume has i t s own overview, w r i t t e n by s c i e n t i s t s o f i n t e r n a t i o n a l s t a t u r e ( i n s e c t i c i d e s , Georghiou; f u n g i c i d e s , Schwinn and Morton; h e r b i c i d e s , L e B a r o n and M c F a r l a n d ) . Thus t h e o b j e c t i v e o f t h i s c h a p t e r i s t o p r o v i d e g e n e r a l information, a p p l i c a b l e across a l l three s e c t i o n s .


The

literature

R e s i s t a n c e Pesearcfr

Previous L i t e r a t u r e . As t h e importance o f r e s i s t a n c e has become a p p a r e n t , a s t e a d i l y i n c r e a s i n g amount o f r e s e a r c h has been done t o u n d e r s t a n d and combat i t . E x c e l l e n t summaries o f e a r l i e r work, with extensive references t o the o r i g i n a l l i t e r a t u r e , are a v a i l a b l e i n r e c e n t books and r e v i e w a r t i c l e s , some d e a l i n g w i t h a l l a r e a s o f agrochemistry and o t h e r s a d d r e s s i n g s p e c i f i c c l a s s e s o f p e s t s ( i n s e c t s , 9-11; f u n g i , 12,13; weeds, 1 4 ) • I n f o r m a t i o n on r e s i s t a n c e t o r o d e n t i c i d e s , a n t i b i o t i c s , and a n t i c o c c i d i a l drugs, w h i c h a r e n o t c o v e r e d i n t h i s volume, i s a v a i l a b l e i n two o f t h e r e f e r e n c e s (7 ,&). Each o f t h e s e works may be recommended f o r i t s s c i e n t i f i c quality. However, one s t a n d s o u t as h a v i n g r e f o c u s e d t h e s u b j e c t , broadened i t s c o n s t i t u e n c y , and h e l p e d c r y s t a l l i z e i n f o r m a t i o n i n t o action. I n 1984, t h e energy b u i l d i n g around r e s i s t a n c e management was c h a n n e l e d i n t o consensus by a N a t i o n a l Academy o f S c i e n c e s (NAS) symposium and workshop, t h e p r o c e e d i n g s o f w h i c h were p u b l i s h e d i n 1986 ( 7 ) . Most n o t a b l y , t h i s was t h e f i r s t m e e t i n g o f i t s k i n d t o i n t e g r a t e s c i e n c e and p u b l i c p o l i c y a c r o s s t h e whole a g r o c h e m i c a l spectrum. What had been c o n f i n e d t o t h e s c i e n t i f i c and commercial realm was expanded t o i n c l u d e g o v e r n m e n t a l f u n c t i o n s , r a n g i n g from r e g i s t r a t i o n t o a n t i t r u s t l e g i s l a t i o n . A s i d e from making t h i s i m p o r t a n t c o n n e c t i o n , and e m p h a s i z i n g i t s p o t e n t i a l f o r implementing a t r u l y i n t e g r a t e d response t o r e s i s t a n c e , t h e symposium and p u b l i c a t i o n a l s o b r o u g h t r e s i s t a n c e management t o t h e a t t e n t i o n o f a b r o a d e r a u d i e n c e , and p r o v i d e d new impetus f o r a c t i o n . Areas needing f u r t h e r r e s e a r c h and c o o p e r a t i o n were i d e n t i f i e d , and t h e i m p o r t a n t p o i n t was made t h a t r e s i s t a n c e management s h o u l d be a f a c t o r i n r e g u l a t o r y d e c i s i o n making f o r new and e x i s t i n g a g r o c h e m i c a l s . The NAS book remains i n v a l u a b l e r e a d i n g today, and we hope t h e c u r r e n t volume, i n w h i c h p u b l i c p o l i c y i s s u e s a r e t r e a t e d by s e v e r a l a u t h o r s , w i l l s e r v e t o update and expand upon i t . C u r r e n t Awareness. S c a n n i n g t h e L i t e r a t u r e C i t e d i n subsequent c h a p t e r s q u i c k l y i d e n t i f i e s j o u r n a l s t o be m o n i t o r e d i n each f i e l d . However, t h e t h e volume o f p r i m a r y l i t e r a t u r e , r e v i e w s , and symposia c h a l l e n g e s even t h e most d i l i g e n t o b s e r v e r . A p r o m i s i n g new v e h i c l e f o r c u r r e n t awareness i s a b i a n n u a l n e w s l e t t e r , p u b l i s h e d by M i c h i g a n S t a t e U n i v e r s i t y i n c o o p e r a t i o n w i t h t h e Western R e g i o n a l Communication Committee on P e s t i c i d e


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AGROCHEMICALS

R e s i s t a n c e and R e s i s t a n c e Management (WRCC-60). T h i s p u b l i c a t i o n , which f i r s t appeared i n J a n u a r y , 1989 {15.) r f e a t u r e s c o n c i s e r e p o r t s on o r i g i n a l r e s e a r c h , d i s t r i b u t i o n o f r e s i s t a n t p e s t s , symposia announcements and p r o c e e d i n g s , l e g i s l a t i v e a c t i v i t y , r e v i e w s , f u n d i n g o p p o r t u n i t i e s , and o t h e r i n f o r m a t i o n on p e s t i c i d e r e s i s t a n c e , drawn from around the w o r l d . Subscription information may be o b t a i n e d from Ms. R o s i e B i c k e r t , P e s t i c i d e R e s e a r c h C e n t e r , M i c h i g a n S t a t e U n i v e r s i t y , E a s t L a n s i n g , MI 48824-1311, U.S.A. Defining

the

Challenge

Scope. The e x t e n t o f r e s i s t a n c e was summarized s u c c i n c t l y by G e o r g h i o u i n 1986: "Whereas the p r e s e n c e o f r e s i s t a n c e was a r a r e phenomenon d u r i n g the e a r l y 1950s, i t i s the f u l l y s u s c e p t i b l e p o p u l a t i o n t h a t i s r a r e i n the 1 9 8 0 s . He goes on t o c i t e r e p o r t s o f r e s i s t a n c e t o 447 s p e c i e s o f i n s e c t s and m i t e s , 100 s p e c i e s of p l a n t pathogens, and 48 s p e c i e s o f weeds, w o r l d wide (1_§). In t h i s volume, he r a i s e s the number f o r i n s e c t s and m i t e s t o 504 s p e c i e s , n o t i n g t h a t t h i s i s d o u b t l e s s a lower l i m i t , and LeBaron and M c F a r l a n d r a i s e the number o f weed s p e c i e s t o 78.


M

Consequences. The impact o f r e s i s t a n c e ranges from i n c r e a s e d c o s t s at the l e a s t , t o c a t a s t r o p h i c c o n t r o l f a i l u r e s and complete l o s s of v a l u a b l e c h e m i c a l t o o l s a t the w o r s t . In any c r o p p i n g system, c e r t a i n a g r o c h e m i c a l s become the c o n t r o l method o f c h o i c e because they o f f e r improvements i n c o s t e f f e c t i v e n e s s , worker s a f e t y , or e n v i r o n m e n t a l impact, r e l a t i v e t o other a v a i l a b l e products. Simple l o g i c i n d i c a t e s t h a t t h e i r l o s s t o r e s i s t a n c e degrades one or more o f t h e s e f a c t o r s . S a f e t y and e n v i r o n m e n t a l i s s u e s can be r e l a t i v e l y c l e a r c u t , as i n the n e g a t i v e consequences o f r e p l a c i n g p y r e t h r o i d s w i t h organophosphorus i n s e c t i c i d e s (see R i l e y , t h i s volume). However, the economics o f r e s i s t a n c e can o n l y be e s t i m a t e d , s i n c e " d e t a i l e d e s t i m a t e s o f c r o p l o s s e s , w i t h and w i t h o u t p e s t i c i d e use, are s t i l l s u r p r i s i n g l y d i f f i c u l t to o b t a i n " (17). A v a i l a b l e d a t a suggest t h a t c o s t s can i n c r e a s e d r a m a t i c a l l y . P i m e n t e l e_£ a l . e s t i m a t e d added c o s t s from i n s e c t i c i d e r e s i s t a n c e i n the U.S. a l o n e a t $13 3 m i l l i o n i n the l a t e 1970s ( 1 8 ) ; e s t i m a t e s were a l s o made o f the economics o f l o s i n g a g r o c h e m i c a l s c o m p l e t e l y ( 1 2 ) . Steiner documented an e v e n t u a l 6 - f o l d r i s e i n the expense o f German a p p l e p r o d u c t i o n as m i t e s became r e s i s t a n t t o a s e r i e s of a c a r i c i d e s over time ( 2 £ ) . M e t c a l f has summarized r e s i s t a n c e - r e l a t e d c o s t s f o r c o n t r o l l i n g mosquito v e c t o r s o f m a l a r i a , showing t h a t e x p e n d i t u r e s can i n c r e a s e up t o 2 0 - f o l d — i n c o u n t r i e s l e a s t able to a f f o r d them — w i t h the end r e s u l t o f i n c r e a s e d m a l a r i a i n c i d e n c e (2JL). C l e a r l y t h e s e r e p r e s e n t but a s m a l l f r a c t i o n o f r e s i s t a n c e c o s t s , and i n the case o f m a l a r i a c o n t r o l one sees t h a t t h e r e can be a s i g n i f i c a n t t o l l i n human terms as w e l l . Many more such a n a l y s e s are needed t o p r o v i d e b e t t e r i n p u t s f o r d e c i s i o n making by growers, i n d u s t r y , and p u b l i c p o l i c y makers. One s h o u l d a l s o r e c o g n i z e t h a t t h e s e are the ' b e t t e r ' c a s e s , where a l t e r n a t i v e c h e m i c a l s are s t i l l a v a i l a b l e . The p o t e n t i a l consequences o f r e s i s t a n c e are perhaps b e s t u n d e r s t o o d by c o n s i d e r -



1.

MOBERG


i n g i n s t a n c e s where a l l a g r o c h e m i c a l s have l o s t e f f e c t i v e n e s s . F o r example, r e s i s t a n c e o f t h e tobacco budworm t o a l l a v a i l a b l e i n s e c t i c i d e s l e d t o t h e v i r t u a l abandonment o f c o t t o n p r o d u c t i o n i n s o u t h e r n Texas and n o r t h e a s t e r n Mexico d u r i n g t h e e a r l y 1970s, w i t h d e v a s t a t i n g consequences t o t h e l o c a l economies (22,21.) • O t h e r cases where r e s i s t a n c e has r e a c h e d c r i s i s p r o p o r t i o n s i n c l u d e C o l o r a d o p o t a t o b e e t l e on Long I s l a n d , New York (1) and diamondback moth i n S o u t h e a s t A s i a (24)• So f a r , t h e w o r s t c a s e s have been c o n f i n e d t o i n s e c t i c i d e s , where t h e h i s t o r y o f r e s i s t a n c e has been l o n g e s t , s e l e c t i o n p r e s s u r e g r e a t e s t , and t h e modes o f a c t i o n a v a i l a b l e fewest. F u n g i c i d e and h e r b i c i d e r e s i s t a n c e c a n c r e a t e s h o r t - t e r m h a r d s h i p s — f o r example, c o n t r o l f a i l u r e s o f benomyl on a p p l e scab i n M i c h i g a n (15) and on grape g r a y mold i n F r a n c e and peanut l e a f s p o t s i n t h e S o u t h e a s t e r n U.S. (1£), l o c a l i z e d d i s t r i b u t i o n s o f t r i a z i n e - r e s i s t a n t weed b i o t y p e s w o r l d wide (14; LeBaron and M c F a r l a n d , G r e s s e l , t h i s volume) — b u t so f a r s e r i o u s c r i s e s have been h e l d a t bay by t h e a v a i l a b i l i t y o f a l t e r n a t e compounds. That t h i s may n o t p e r s i s t , however, i s i l l u s t r a t e d by t h e r e c e n t discovery of multiple resistance to several classes of herbicides i n b i o t y p e s o f r y e g r a s s i n A u s t r a l i a (Powles e_£ si.., LeBaron and M c F a r l a n d , t h i s volume) and b l a c k g r a s s i n t h e U n i t e d Kingdom (Kemp e_t aJL., t h i s volume). Prospects. S e v e r a l c o n c l u s i o n s c a n be drawn from t h e f o r e g o i n g . F i r s t , r e s i s t a n c e i s s t e a d i l y s p r e a d i n g , i n terms o f p e s t s p e c i e s , c l a s s e s o f a g r o c h e m i c a l s , and g e o g r a p h i c l o c a t i o n . Second, c o s t s , though d i f f i c u l t t o e s t i m a t e w i t h p r e c i s i o n , a r e u n d o u b t e d l y g r e a t , and c a n e x t e n d beyond mere economics t o r e a l human s u f f e r i n g . T h i r d , c r i s i s s i t u a t i o n s a r e , f o r t u n a t e l y , n o t y e t t h e norm. I n most i n s t a n c e s , t h e r e i s s t i l l time t o p l a n and t o a c t . Fourth, d e l a y c o u l d be c o s t l y , and even d i s a s t r o u s . C r i s e s c a n and do o c c u r when a l l a v a i l a b l e c o n t r o l methods f a i l . In a c a r e f u l l y r e a s o n e d l o o k t o t h e f u t u r e ( 2 7 ) , Conway concluded t h a t "At the world l e v e l , there i s l i t t l e t o support the a s s e r t i o n t h a t ... t h e r e i s a t h r e a t now o r i n t h e f o r e s e e a b l e f u t u r e t o g l o b a l f o o d s u p p l i e s ... Of g r e a t e r l i k e l i h o o d ... i s t h e b u i l d up o f a [ l o c a l i z e d ] r e s i s t a n c e problem t o t h e p o i n t a t which n a t i o n a l and r e g i o n a l f o o d p r o d u c t i o n i s t h r e a t e n e d . " Potential t r o u b l e s p o t s were i d e n t i f i e d as wheat, c o r n , o r soybean p r o d u c t i o n i n t h e U.S.; wheat o r r o o t c r o p s i n Europe; wheat o r r i c e i n I n d i a ; and r i c e o r v e g e t a b l e s i n s o u t h e a s t A s i a , C h i n a o r Japan. Any one " c o u l d s e v e r e l y a f f e c t r e g i o n a l f o o d p r o d u c t i o n and have e x t e n s i v e r e p e r c u s s i o n s on t h e g l o b a l f o o d m a r k e t s . " Success or f a i l u r e depends upon "smoothness o f s u b s t i t u t i o n " — a r e m u l t i p l e c o n t r o l a l t e r n a t i v e s , c h e m i c a l and n o n - c h e m i c a l , a v a i l a b l e ; i f s o , w i l l t h e y be used i n an i n t e g r a t e d f a s h i o n , and w i l l enough growers cooperate? In t h i s c o n n e c t i o n , Conway does p o i n t t o one " t e n a b l e g l o b a l t h r e a t " : a g r o c h e m i c a l d i s c o v e r y and m a n u f a c t u r e i s i n c r e a s i n g l y c o n c e n t r a t e d i n a few companies, and s h o u l d one o r more d e c i d e t o abandon i n s e c t i c i d e r e s e a r c h i n f a v o r o f "more p r o f i t a b l e p e s t i c i d e s " t h e t h r e a t t o f o o d p r o d u c t i o n would be s e r i o u s (17).


5


6


AGROCHEMICALS

The same c o u l d be s a i d o f f u n g i c i d e r e s e a r c h , w h i c h h i s t o r i c a l l y has been c o n c e n t r a t e d i n even fewer companies than i n s e c t i c i d e research. Taken t o g e t h e r , the scope, consequences, and f u t u r e o u t l o o k f o r r e s i s t a n c e are a c l e a r c a l l to a c t i o n . F o r t u n a t e l y , succeeding c h a p t e r s show t h a t t h i s c a l l i s b e i n g heeded, i n c r e a t i v e and c o o p e r a t i v e ways. Moreover, the r o b u s t a g r o c h e m i c a l p a t e n t l i t e r a t u r e , w h i c h d e m o n s t r a t e s c o n t i n u i n g r e s e a r c h d i r e c t e d toward new i n s e c t i c i d e s , a c a r i c i d e s and f u n g i c i d e s , and the growing commitment o f i n d u s t r y t o r e s i s t a n c e management (see below), show no e v i d e n c e o f d e c l i n i n g i n t e r e s t i n t h e s e c r i t i c a l a r e a s . I n d u s t r i a l c o n s o l i d a t i o n has a d m i t t e d l y p l a c e d s t r a t e g i c d e c i s i o n making i n fewer hands, but i t has a l s o g e n e r a l l y been u n d e r t a k e n w i t h the i n t e n t o f e s t a b l i s h i n g the b r o a d e s t p o s s i b l e p r o d u c t lines. One can even argue t h a t the r e s u l t i n g r e s e a r c h o r g a n i z a t i o n s , having g r e a t e r resources than t h e i r s m a l l e r p r e d e c e s s o r s , w i l l be b e t t e r a b l e and more w i l l i n g t o r e t a i n a l l a r e a s o f a g r o c h e m i c a l d i s c o v e r y , w i t h the i n t e n t o f m a i n t a i n i n g a broad o f f e r i n g to t h e i r customers. The

Nature of

Resistance

To c r e a t e the means — and i n d e e d , the w i l l — t o combat r e s i s t a n c e , one must f i r s t u n d e r s t a n d i t . Though the d e t a i l s o f each s p e c i f i c s i t u a t i o n a r e complex, the g e n e r a l n a t u r e o f r e s i s t a n c e can be u n d e r s t o o d i n terms o f g e n e t i c s and n a t u r a l selection. A N a t u r a l Phenomenon. Each o r g a n i s m i n the complex n a t u r a l w o r l d around us i s a s u r v i v o r . Through e v o l u t i o n a r y p r o c e s s e s e x t e n d i n g over m i l l e n n i a , e v e r y s p e c i e s o f p l a n t and animal has adapted t o cope w i t h the p h y s i c a l c o n d i t i o n s and compete w i t h the o t h e r organisms i n i t s e c o l o g i c a l n i c h e , so t h a t r e p r o d u c t i o n o f s u f f i c i e n t i n d i v i d u a l s , and thus s u r v i v a l o f the s p e c i e s , i s assured. The a t t r i b u t e s needed are s u p p l i e d by the g e n e t i c d i v e r s i t y o f l a r g e p o p u l a t i o n s : p r o v i d e d even a s m a l l number o f i n d i v i d u a l s w i t h the r e q u i r e d c h a r a c t e r i s t i c s are p r e s e n t , they can s u r v i v e and pass t h e s e t r a i t s on t o progeny, which can i n time become common i n the p o p u l a t i o n . A g r i c u l t u r a l p e s t s are no e x c e p t i o n . In f a c t , t h e y are c h a r a c t e r i z e d by v e r y l a r g e p o p u l a t i o n s and f r e q u e n t r e p r o d u c t i o n , and a r e o f t e n even more a d a p t a b l e to a d v e r s e c o n d i t i o n s than o t h e r organisms. From t h i s p e r s p e c t i v e , c h e m i c a l s used t o c o n t r o l them s h o u l d be seen as o n l y the l a t e s t i n a l o n g h i s t o r y o f t h r e a t s t o their survival. T h e r e f o r e , i t s h o u l d come as no s u r p r i s e t h a t many p e s t s p o s s e s s means t o r e s i s t the l e t h a l e f f e c t s o f a g r o c h e m i c a l s . Indeed, w i t h o u t c l a i m i n g t h a t r e s i s t a n c e w i l l o c c u r i n e v e r y case, i t seems l o g i c a l t h a t the w i s e s t approach t o any p e s t - a g r o c h e m i c a l i n t e r a c t i o n s h o u l d not be t o ask whether r e s i s t a n c e w i l l d e v e l o p , but when, and i n what form. The same must be e x p e c t e d f o r g e n e t i c , b i o l o g i c a l , o r even m e c h a n i c a l c o n t r o l measures.


1.

MOBERG



A Manageable C h a l l e n g e . A t t h e same time, t h e r e a r e p o s i t i v e aspects i n the r e a l i z a t i o n that r e s i s t a n c e i s p a r t of a l a r g e r , ongoing b i o l o g i c a l process. As a n a t u r a l phenomenon, c o n t r o l l e d by g e n e t i c s and e x p r e s s e d i n s p e c i f i c b i o c h e m i c a l p r o c e s s e s , r e s i s t a n c e c a n be s t u d i e d , u n d e r s t o o d , and combated. I t i s neither m y s t e r i o u s n o r t o t a l l y beyond our c o n t r o l . T h i s i s p a r t i c u l a r l y t r u e i f s t r a t e g i e s and t a c t i c s t o a v o i d o r d e l a y r e s i s t a n c e a r e implemented p r o a c t i v e l y , b e f o r e r e s i s t a n t p e s t s become s e r i o u s problems; i . e . b e f o r e t h e s u r v i v a l c h a r a c t e r i s t i c s become common i n the population. Moreover, r e s i s t a n c e i s n o t something new and s i n i s t e r , u n l e a s h e d on t h e w o r l d by use o f a g r o c h e m i c a l s . I t i s a fact of n a t u r e t h a t must be i n t e g r a t e d i n t o t h e d i s c o v e r y and development o f new p r o d u c t s and t h e use o f e x i s t i n g ones. Definitions One might e x p e c t t h a t terms r e l a t i n g t o r e s i s t a n c e would be s t a n d a r d i z e d by now. However, they a r e s t i l l b e i n g d e b a t e d and r e f i n e d , as c a n be seen by c o n s i d e r i n g t h e word ' r e s i s t a n c e ' itself. 'Resistance'. F o r many y e a r s t h i s word meant d i f f e r e n t t h i n g s t o d i f f e r e n t p e o p l e , and was used i n t e r c h a n g e a b l y w i t h ' t o l e r a n c e ' and 'insensitivity'. I n 1960, Crow emphasized t h e importance o f g e n e t i c s by d e f i n i n g r e s i s t a n c e as "a g e n e t i c change i n r e s p o n s e t o s e l e c t i o n " (££). I n 1971, t h e World H e a l t h O r g a n i z a t i o n p r o p o s e d a s t a n d a r d i z e d d e f i n i t i o n f o r r e s i s t a n c e t o i n s e c t i c i d e s : "The development o f an a b i l i t y i n a s t r a i n o f i n s e c t s t o t o l e r a t e doses o f t o x i c a n t w h i c h would p r o v e l e t h a l t o t h e m a j o r i t y o f i n d i v i d u a l s i n a normal p o p u l a t i o n o f t h e same s p e c i e s " (12). Subsequently, the U n i t e d N a t i o n s Food and A g r i c u l t u r e O r g a n i z a t i o n (FAO) p r o p o s e d a s i m i l a r d e f i n i t i o n f o r f u n g i c i d e s and b a c t e r i c i d e s , a d d i n g t h e g e n e t i c q u a l i f i e r t h a t r e s i s t a n c e be l i m i t e d t o " h e r e d i t a b l e changes" (1£). ' T o l e r a n c e ' o r ' i n s e n s i t i v i t y ' were d i s c o u r a g e d as ambiguous. Some c o n f u s i o n p e r s i s t s , however, s i n c e ' r e s i s t a n c e ' i s a l s o used by p l a n t p a t h o l o g i s t s t o denote t h e a b i l i t y o f p l a n t s t o r e s i s t a t t a c k by pathogens. I n weed s c i e n c e , m u l t i p l e terms a r e s t i l l used; f o r example, i n t h e d e f i n i t i o n s o f G r e s s e l : " T o l e r a n c e i s d e f i n e d as any d e c r e a s e i n s u s c e p t i b i l i t y , compared w i t h t h e w i l d type. R e s i s t a n c e i s complete t o l e r a n c e t o a g r i c u l t u r a l l y used l e v e l s o f a h e r b i c i d e " (31)• In g e n e r a l , i t appears t h a t v a r i a n t s o f t h e FAO d e f i n i t i o n a r e now g a i n i n g ground. However, two somewhat i n t e r r e l a t e d problems remain. F i r s t , what i s t h e 'normal' r e f e r e n c e p o p u l a t i o n , a g a i n s t w h i c h d e c r e a s e s i n s e n s i t i v i t y s h o u l d be measured? Initially, 'normal' meant p e s t p o p u l a t i o n s never s u b j e c t e d t o t o x i c a n t p r e s s u r e and m a i n t a i n e d i n t h e l a b o r a t o r y (12). However, t h e r e i s now growing s e n t i m e n t t h a t m e a n i n g f u l r e s u l t s r e q u i r e u s i n g f i e l d - c o l l e c t e d 'normal' p o p u l a t i o n s w i t h a 'normal' h i s t o r y o f a g r o c h e m i c a l exposure f o r t h e a r e a i n q u e s t i o n ; t h e s e may a l r e a d y be r e s i s t a n t t o t h e t o x i c a n t i n q u e s t i o n , o r may d i s p l a y c r o s s


7


8

MANAGING

RESISTANCE TO

AGROCHEMICALS

r e s i s t a n c e i n the case o f new compounds (11). The key d i f f i c u l t y here i s proper m o n i t o r i n g to e s t a b l i s h meaningful b a s e l i n e data (34; see a l s o B u l l , R i l e y , C r o f t , B r e n t , D e l p and Wade, t h i s volume). Second, how s h o u l d l a b o r a t o r y and f i e l d s t u d i e s o f r e s i s t a n c e be c o r r e l a t e d ? Laboratory studies n e c e s s a r i l y involve small c o l l e c t i o n s of i n d i v i d u a l s , whereas f i e l d r e s i s t a n c e i s dependent on the d i s t r i b u t i o n and s t a b i l i t y o f r e s i s t a n c e l e v e l s a c r o s s a whole f i e l d p o p u l a t i o n ; moreover, ' d i s c r i m i n a t i n g d o s e s ' used i n t h e s e s t u d i e s may bear l i t t l e r e l a t i o n t o r e s i d u e s r e s u l t i n g from recommended f i e l d a p p l i c a t i o n r a t e s . Thus l a b o r a t o r y s t u d i e s can e r r i n e i t h e r d i r e c t i o n , c a u s i n g unwarranted c o n c e r n i n some c a s e s or f a i l i n g t o i n d i c a t e r e a l r i s k s i n o t h e r s (see Schwinn and Morton, t h i s volume, f o r an example i n v o l v i n g phenylamide f u n g i c i d e s ) . At the same time, f i e l d ' r e s i s t a n c e ' can sometimes be t r a c e d to poor a p p l i c a t i o n t e c h n i q u e s or t i m i n g , or even t o l o w - q u a l i t y p r o d u c t s (14). Thus r e s e a r c h e r s u s u a l l y d i f f e r e n t i a t e ' f i e l d ' r e s i s t a n c e from ' l a b o r a t o r y ' o r ' p h y s i o l o g i c a l ' r e s i s t a n c e , a d i s t i n c t i o n w h i c h we f a v o r . Recently, a d e f i n i t i o n that t r i e s to take these f a c t o r s i n t o a c c o u n t has been o f f e r e d by S a w i c k i : " R e s i s t a n c e marks a g e n e t i c change i n r e s p o n s e t o s e l e c t i o n by t o x i c a n t s t h a t may impair c o n t r o l i n the f i e l d " (14). One might w e l l add " a t recommended a p p l i c a t i o n r a t e s . " In any e v e n t , the v e r y l e n g t h o f the d i s c u s s i o n above shows t h a t more c o n f o r m i t y i s r e q u i r e d on t h i s s i m p l e but i m p o r t a n t i s s u e . 'Cross R e s i s t a n c e ' . T h i s s e e m i n g l y s i m p l e term i s a l s o s u b j e c t to v a r i o u s i n t e r p r e t a t i o n s . I t i s p r o b a b l y b e s t d e f i n e d as r e s i s t a n c e of an organism t o two o r more t o x i c a n t s ( w i t h the i m p l i c a t i o n t h a t the 'normal' p o p u l a t i o n i s s e n s i t i v e t o b o t h ) . R e c e n t l y the added q u a l i f i e r ' p o s i t i v e ' or ' p o s i t i v e l y c o r r e l a t e d ' c r o s s r e s i s t a n c e has been s u g g e s t e d , s i n c e t h e r e are i n s t a n c e s where r e s i s t a n c e to one t o x i c a n t i s accompanied by i n c r e a s e d s e n s i t i v i t y t o a n o t h e r , w h i c h are t h e n termed ' n e g a t i v e ' or ' n e g a t i v e l y c o r r e l a t e d ' c r o s s resistance. ( F o r an example, see F u j i m u r a , I s h i i , t h i s volume.) T h i s d i s t i n c t i o n , though u s e f u l , seems cumbersome and p o s s i b l y c o n f u s i n g as p r e s e n t l y worded. Moreover, t h e r e are s u b c l a s s e s o f c r o s s r e s i s t a n c e , d e f i n e d a c c o r d i n g to t h e i r g e n e t i c and m e c h a n i s t i c b a s i s . Cross r e s i s t a n c e m e d i a t e d fey. a. s i n g l e gene ('monogenic' or 'monof a c t o r i a l ' ) may be due e i t h e r t o a s i n g l e d e f e n s e mechanism o p e r a t i n g a g a i n s t b o t h t o x i c a n t s ( t h i s i s sometimes g i v e n as the s o l e d e f i n i t i o n o f c r o s s r e s i s t a n c e ) , or t o m u l t i p l e mechanisms t h a t may not a c t e q u a l l y on d i f f e r e n t t o x i c a n t s ( ' p l e i o t r o p i c r e s i s t a n c e ' ) . The l a t t e r can sometimes be t r a c e d t o a r e g u l a t o r y gene i n f l u e n c i n g s e v e r a l o t h e r s

(1£). C r o s s r e s i s t a n c e m e d i a t e d by m u l t i p l e genes ( ' p o l y g e n i c ' or ' p o l y f a c t o r i a l ' ) may, s i m i l a r l y , r e s u l t from the same o v e r a l l mechanism(s) a c t i n g a g a i n s t b o t h t o x i c a n t s , o r from d i f f e r e n t mechanisms a c t i n g a g a i n s t each. The l a t t e r case i s sometimes c a l l e d ' m u l t i p l e r e s i s t a n c e ' , but t h i s seems ambiguous. The broader d e f i n i t i o n of 'multiple r e s i s t a n c e ' or ' m u l t i r e s i s t a n c e '


1.

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as " h a v i n g a genotype [ t o t a l g e n e t i c c o n s t i t u t i o n ] c o n f e r r i n g r e s i s t a n c e t o a wide range o f p e s t i c i d e g r o u p s " {33.) would seem preferable. The r e a d e r who f i n d s t h i s c o n f u s i n g cannot be blamed. Communication i n s i d e and o u t s i d e t h e community o f r e s i s t a n c e r e s e a r c h e r s would b e n e f i t from b e t t e r s t a n d a r d i z a t i o n o f terms.


R e l a t e d G e n e t i c Terms. Though an e x t e n s i v e d i s c u s s i o n i s beyond the scope o f t h i s c h a p t e r , i t may be h e l p f u l t o d e f i n e a few terms commonly a p p e a r i n g i n r e s i s t a n c e l i t e r a t u r e ( a d a p t e d from 3 6 ) ;

-

-

Chromosomes. DNA polymers t h a t c a r r y genes i n l i n e a r a r r a n g e ment. E x c e p t f o r s p e c i a l i z e d c e l l s formed f o r s e x u a l r e p r o d u c t i o n , chromosomes o c c u r as matched ('homologous') p a i r s i n each c e l l o f an o r g a n i s m . Gene. A s h o r t l e n g t h o f a chromosome i n f l u e n c i n g a p a r t i c u l a r s e t o f t h e organism's c h a r a c t e r i s t i c s . T h i s s e t o f c h a r a c t e r i s t i c s i s sometimes c a l l e d a ' t r a i t ' . Alleles. D i f f e r e n t forms o f a gene ( i . e . , c o d i n g f o r v a r i a n t s o f t h e same t r a i t ) . Homozygous. H a v i n g i d e n t i c a l a l l e l e s o f a g i v e n gene i n b o t h homologous chromosomes. The i n d i v i d u a l i s a 'homozygote'. Heterozygous. H a v i n g d i f f e r e n t a l l e l e s o f a g i v e n gene i n each chromosome o f t h e homologous p a i r . The i n d i v i d u a l i s a 'heterozygote'. Dominant Gene. An a l l e l e t h a t p a r t i a l l y o r w h o l l y o v e r r i d e s t h e e f f e c t of i t s paired a l l e l e i n a heterozygote. R e c e s s i v e Gene. An a l l e l e h a v i n g no e f f e c t on t h e organism u n l e s s homozygous.

Historical

Perspective

E x c e p t i o n a l l y comprehensive, t h o u g h t f u l c o v e r a g e o f t h e h i s t o r y o f r e s i s t a n c e may be found i n a paper o f G e o r g h i o u and M e l l o n ( " P e s t i c i d e R e s i s t a n c e i n Time and Space", 12) and i n a more r e c e n t update by G e o r g h i o u (11). T h i s s e c t i o n o f f e r s a much a b b r e v i a t e d summary, f o l l o w e d by s p e c u l a t i o n s on why r e s i s t a n c e d e v e l o p e d as i t d i d and o b s e r v a t i o n s on t h e response o f i n d u s t r y . The S t e p w i s e P r o g r e s s i o n o f R e s i s t a n c e . R e s i s t a n c e was f i r s t noted f o r i n s e c t s , when Melander r e p o r t e d i n 1914 t h a t San J o s e s c a l e on a p p l e s i n Washington S t a t e had become i n s e n s i t i v e t o l i m e - s u l f u r (12)• T h i s was g r e e t e d w i t h some s k e p t i c i s m , and was f o l l o w e d by s c a t t e r e d r e p o r t s , l i m i t e d t o i n s e c t s , over t h e n e x t 30 y e a r s . By 1946, r e s i s t a n c e was documented f o r o n l y 11 s p e c i e s ( 4 0 ) . The p i c t u r e changed r a p i d l y a f t e r i n t r o d u c t i o n o f t h e p o t e n t and p e r s i s t e n t compound, DDT. DDT r e s i s t a n c e appeared q u i c k l y , w o r l d wide, and i n s e v e r a l s p e c i e s , f o l l o w i n g t h e f i r s t r e p o r t i n 1947 (11)• New i n s e c t i c i d e s were i n t r o d u c e d s t e a d i l y , p r o v i d i n g b e t t e r c o n t r o l o f b o t h r e s i s t a n t and s u s c e p t i b l e i n s e c t s , b u t most new p r o d u c t s e v e n t u a l l y s u f f e r e d t h e same f a t e . The number o f s p e c i e s showing r e s i s t a n c e t o one o r more t o x i c a n t d o u b l e d about e v e r y s i x y e a r s between 1948 and 1983 ( 3 7 ) .


9


10

MANAGING RESISTANCE TO AGROCHEMICALS

Y e t even as t h i s happened, t h e p r e v a i l i n g o p i n i o n was t h a t o t h e r a g r o c h e m i c a l s would e n c o u n t e r r e s i s t a n c e r a r e l y , i f a t a l l . Indeed, t h e s t o r y f o r f u n g i c i d e s p a r a l l e l s t h a t f o r i n s e c t i c i d e s remarkably. Though r e s i s t a n c e was f i r s t r e p o r t e d f o r P e n i c i l l i u m spp. t o b i p h e n y l i n 1940 by F a r k a s and Aman (41), 27 y e a r s l a t e r G e o r g o p o u l o s and Z a r a c o v i t i s n o t e d t h a t "The r e p o r t e d cases o f t o l e r a n c e t o a g r i c u l t u r a l f u n g i c i d e s a r e v e r y few, and t h e knowledge accumulated h a r d l y j u s t i f i e s a r e v i e w " (41). However, i n the e a r l y 1970s new, h i g h l y a c t i v e s y s t e m i c compounds such as benomyl d i d f o r f u n g i c i d e s what DDT had done f o r i n s e c t i c i d e s . R e s i s t a n c e appeared i n a m a t t e r o f y e a r s , and some uses were l o s t t h a t have n o t been r e c o v e r e d t o t h i s day (!£). Some degree o f r e s i s t a n c e has now become t h e norm f o r a l l c l a s s e s o f f u n g i c i d e s , w i t h t h e e x c e p t i o n o f a few p r o t e c t a n t compounds. The f i n a l s t a g e — h e r b i c i d e r e s i s t a n c e — i s now upon us. H e r b i c i d e s were l o n g thought s a f e from r e s i s t a n c e because weeds l a c k t h e m o b i l i t y and r a p i d r e p r o d u c t i o n o f i n s e c t s and f u n g i , and because a few s u s c e p t i b l e i n d i v i d u a l s s u r v i v i n g t r e a t m e n t can produce l a r g e numbers o f seeds t h a t c a n i n f e s t t h e s o i l seed bank and g e r m i n a t e o v e r many y e a r s . F i e l d r e s i s t a n c e o f common g r o u n d s e l t o t r i a z i n e s i n Washington S t a t e was f i r s t r e p o r t e d i n 1970 ( 4 £ K b u t r e s i s t a n c e was slow t o s p r e a d , and 13 y e a r s l a t e r R a d o s e v i c h wrote t h a t "... t h e r e a r e few examples o f f o r m e r l y s u s c e p t i b l e weed s p e c i e s t h a t have d e v e l o p e d r e s i s t a n c e " ( 4 5 ) • T h i s has changed d r a m a t i c a l l y i n r e c e n t y e a r s , as i s a p p a r e n t t h r o u g h o u t t h e h e r b i c i d e c h a p t e r s o f t h i s book. Of p a r t i c u l a r note are t h e s u r p r i s i n g speed o f r e s i s t a n c e development t o a c e t o l a c t a t e s y n t h a s e i n h i b i t o r s (Mazur e_£ a l . , G r e s s e l , t h i s volume), and t h e emergence o f m u l t i p l y r e s i s t a n t r y e g r a s s and b l a c k g r a s s biotypes noted e a r l i e r . A Common T h r e a d . Though each s t a g e i n t h e h i s t o r y o f r e s i s t a n c e took many by s u r p r i s e , h i n d s i g h t shows common c h a r a c t e r i s t i c s . As l o n g as a c l a s s o f a g r o c h e m i c a l was dominated by r e l a t i v e l y i n e f f i c i e n t , s h o r t r e s i d u a l compounds, s e l e c t i o n p r e s s u r e was low, and r e s i s t a n c e was slow t o d e v e l o p . T h i s was e s p e c i a l l y t r u e f o r the e a r l i e s t i n s e c t i c i d e s and f u n g i c i d e s , w h i c h i n t e r f e r e d w i t h m u l t i p l e b i o c h e m i c a l p r o c e s s e s a t t h e expense o f s e l e c t i v i t y , o r had l i m i t e d p e r s i s t e n c e ( e . g . , b o t a n i c a l i n s e c t i c i d e s ) . But as soon as compounds o f f e r i n g h i g h e f f e c t i v e k i l l , l o n g r e s i d u a l , and s e l e c t i v i t y t h r o u g h a c t i o n a t a s i n g l e b i o c h e m i c a l t a r g e t s i t e appeared, s e l e c t i o n p r e s s u r e was h i g h , and r e s i s t a n c e soon followed. I r o n i c a l l y , t h e seeds o f r e s i s t a n c e were c a r r i e d i n t h e v e r y p r o p e r t i e s t h a t made many p r o d u c t s seem more d e s i r a b l e — i n some c a s e s , s t r i k i n g l y so — t h a n t h e i r p r e d e c e s s o r s . Moreover, t h e e f f i c a c y o f such p r o d u c t s o f t e n l e d t o t h e unwise p r a c t i c e o f r e l y i n g on a s i n g l e compound o r c l a s s o f compounds over one o r more s e a s o n s , e x a c e r b a t i n g t h e problem t h r o u g h i n c r e a s e d s e l e c t i o n pressure. We must l e a r n and a p p l y t h e b a s i c p r i n c i p l e s o f t h i s h i s t o r y i f we a r e t o improve upon the poor performance o u t l i n e d above, and t h i s t o p i c forms an i m p o r t a n t p a r t o f many o f the


1.

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c h a p t e r s t h a t f o l l o w . One p o i n t d e s e r v i n g reemphasis here i s the importance o f m a i n t a i n i n g the maximum number o f c o n t r o l o p t i o n s f o r a g i v e n c r o p - p e s t complex, d e v e l o p i n g new o p t i o n s , and u s i n g a l l o p t i o n s i n an i n t e g r a t e d manner t o g i v e e a c h the maximum effective l i f e . A p a r t i c u l a r c o r o l l a r y f o r c h e m i s t s and o t h e r d i s c o v e r y s c i e n t i s t s i s the importance o f compounds w i t h new modes of a c t i o n . I n d u s t r y Involvement. A g r o c h e m i c a l companies d i d not escape b e i n g caught o f f g u a r d by the r e l e n t l e s s p r o g r e s s i o n o f r e s i s t a n c e , nor was t h e i r r e s p o n s e e i t h e r c o o r d i n a t e d or u n i f o r m l y e f f e c t i v e a t first. In a c a n d i d assessment o f the e a r l y days o f r e s i s t a n c e management, D e l p wrote t h a t " I n d u s t r y ' s response t o f u n g i c i d e r e s i s t a n c e problems v a r i e s from d e n i a l t o a c t i v e p a r t i c i p a t i o n i n the s o l u t i o n " (4ji). H a p p i l y , t h i s s t a n c e has e v o l v e d r a p i d l y t o a c o o r d i n a t e d , p o s i t i v e response. At f i r s t , the ' s o l u t i o n ' t o r e s i s t a n c e was seen as new compounds, but the i n c r e a s i n g expense o f d i s c o v e r y and the a c c e l e r a t i n g pace o f r e s i s t a n c e development soon l e d t o the r e a l i z a t i o n t h a t good p r o d u c t s t e w a r d s h i p must i n c l u d e r e s i s t a n c e management. I t was a l s o c l e a r t h a t , because o f the v a r i o u s forms of c r o s s r e s i s t a n c e , no one company c o u l d a c t i n i s o l a t i o n . The r e s u l t was i n d u s t r y c o o p e r a t i o n i n wide v a r i e t y o f programs, i n c l u d i n g governmental i n t i a t i v e s such as the A u s t r a l i a n Wheat Board Working P a r t y on G r a i n P r o t e c t a n t s i n the e a r l y 1970s (47.), inter-company w o r k i n g groups such as the P y r e t h r o i d E f f i c a c y Group (PEG, 1979), and s c i e n t i f i c s o c i e t y - b a s e d groups such as the H e r b i c i d e R e s i s t a n t Weeds Committee o f the Weed S c i e n c e S o c i e t y of A m e r i c a (1986). Meanwhile, a b r o a d framework f o r inter-company c o o p e r a t i o n was p r o v i d e d w i t h i n the I n t e r n a t i o n a l Group o f N a t i o n a l A s s o c i a t i o n s of Agrochemical Manufacturers ( g e n e r a l l y known as GIFAP, the acronym f o r the F r e n c h v e r s i o n o f i t s name). A F u n g i c i d e R e s i s t a n c e A c t i o n Committee (FRAC) was formed i n 1981, f o l l o w e d by s i m i l a r groups f o r i n s e c t i c i d e s (IRAC, 1984) and h e r b i c i d e s (HRAC, 1989). D e s p i t e c o n s t r a i n t s o f commercial r i v a l r y , a n t i t r u s t laws, and intra-company d i f f e r e n c e s between r e s e a r c h and m a r k e t i n g s t a f f s ( U ) , t h e s e groups have t a k e n a l e a d e r s h i p r o l e i n t h e i r r e s p e c t i v e a r e a s and have t r i e d t o f o s t e r b o t h inter-company c o o p e r a t i o n and communication o f i n d u s t r y w i t h u n i v e r s i t i e s and government a g e n c i e s ( R i l e y , D e l p and Wade, t h i s volume; LeBaron, H. M., Ciba-Geigy, 1989, p e r s o n a l communication). P r o g r e s s has been slow but s t e a d y , and t h e s e e f f o r t s bode w e l l f o r the f u t u r e . Conclusions R e a c t i o n s t o r e s i s t a n c e have i n c l u d e d s u r p r i s e , d e n i a l , p a n i c , and resignation. The b r i e f h i s t o r y p r e s e n t e d above i s not a b r i g h t one: i n some cases we have been slow t o r e s p o n d t o the c h a l l e n g e , and i n o t h e r s we have f a i l e d to a p p l y l e s s o n s l e a r n e d i n one a r e a to a c t u a l or p o t e n t i a l r e s i s t a n c e problems i n a n o t h e r . Today, none of t h i s i s w a r r a n t e d .


11


12

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RESISTANCE TO

AGROCHEMICALS

On the one hand, r e s i s t a n c e i s c l e a r l y a s e r i o u s c h a l l e n g e . It i s a n a t u r a l phenomenon t h a t w i l l not go away, and i t s consequences can be s e v e r e f o r w o r l d a g r i c u l t u r a l m a r k e t s , p u b l i c h e a l t h , and worldwide s t a n d a r d s o f l i v i n g . On the o t h e r hand, r e s i s t a n c e can be u n d e r s t o o d and combated. A d i s c u s s i o n o f the t e c h n o l o g i e s a v a i l a b l e t o do t h i s i s beyond the scope o f t h i s c h a p t e r , but l o o k i n g f o r w a r d t o s u c c e e d i n g c h a p t e r s one sees t h a t the s c i e n c e we need i s e i t h e r i n hand, or w i t h i n our g r a s p i f r e s e a r c h i s p r o p e r l y f o c u s e d and funded. Many gaps remain t o be f i l l e d , but the f o u n d a t i o n s have been l a i d and the f u t u r e needs have been c l a r i f i e d . What are needed most — and what have o f t e n been most d i f f i c u l t to achieve — are communication and c o o p e r a t i o n . These two f a c t o r s are i n t e r r e l a t e d , and e s s e n t i a l a t b o t h fundamental and p r a c t i c a l levels. For e x i s t i n g r e s i s t a n c e problems, no i n d i v i d u a l grower, r e s e a r c h e r , or company can d e s i g n and implement e f f e c t i v e s o l u t i o n s in isolation. The p e s t s are too m o b i l e and r e s i l i e n t , and the c h e m i c a l t o o l s a v a i l a b l e are too few i n number and too l i m i t e d i n modes o f a c t i o n f o r a n y t h i n g but a c o o r d i n a t e d e f f o r t t o s u c c e e d . We must g e t the most from what we have, b a s i n g p r a c t i c a l measures on the b e s t knowledge a v a i l a b l e . And we must look beyond s h o r t term p r o f i t s or o t h e r c o n s i d e r a t i o n s o f narrow s e l f i n t e r e s t , to the l o n g - t e r m v i a b i l i t y o f c r o p p r o t e c t i o n c h e m i c a l s and the i n d u s t r y t h a t p r o v i d e s them. For the f u t u r e , we need t o s t i m u l a t e and f o c u s b a s i c r e s e a r c h , making s u r e t h a t a l l d i s c i p l i n e s are b r o u g h t t o bear i n a c o o r d i n a t e d way. We must b u i l d u n d e r s t a n d i n g i n growers, whose c o o p e r a t i o n i s e s s e n t i a l f o r p r a c t i c a l s u c c e s s , and who may have t o s e t t l e f o r l e s s t h a n p e r f e c t p e s t c o n t r o l t o r e a l i z e the l o n g - t e r m b e n e f i t o f p r e s e r v i n g a g r o c h e m i c a l e f f i c a c y . The same i s t r u e f o r p u b l i c p o l i c y makers, who need t o u n d e r s t a n d the r e a l v a l u e of a g r o c h e m i c a l s , the importance o f m a i n t a i n i n g the maximum number o f p e s t c o n t r o l o p t i o n s , and the importance o f r e s i s t a n c e management i n b e n e f i t a n a l y s i s . F i n a l l y , i t w i l l be c r i t i c a l t o i n c o r p o r a t e a n t i - r e s i s t a n c e s t r a t e g i e s b o t h i n new compound d i s c o v e r y and i n the e a r l i e s t s t a g e s o f new p r o d u c t development and i n t r o d u c t i o n . F o r t u n a t e l y , t h e r e are c l e a r s i g n s t h a t communication can l e a d t o c o o p e r a t i o n and w e l l - t a r g e t e d r e s e a r c h , and t h a t t h e s e i n t u r n can l e a d t o s u c c e s s f u l r e s i s t a n c e management. In the c h a p t e r s ahead, examples i n c l u d e p r o a c t i v e approaches t o a c a r i c i d e r e s i s t a n c e ( C r o f t ) , government-industry cooperation i n p y r e t h r o i d r e s i s t a n c e management ( B u l l , R i l e y ) , g e n e t i c e n g i n e e r i n g t o p r o v i d e new h e r b i c i d e o p t i o n s i n a v a r i e t y of c r o p s (Mazur e_£ s i . , Newhouse e_£ aJL.; see a l s o 1,4) and new i n s e c t i c i d e s t a r g e t i n g r e s i s t a n t p o p u l a t i o n s ( G e l e r n t e r ) , s u c c e s s f u l management o f phenylamide f u n g i c i d e r e s i s t a n c e (Schwinn and M o r t o n ) , the development o f s h o r t - r e s i d u a l compounds t o manage s u l f o n y l u r e a h e r b i c i d e r e s i s t a n c e (Mazur e_£ a l . ) , and the f i r s t p r a c t i c a l d e m o n s t r a t i o n o f the u t i l i t y o f n e g a t i v e l y c o r r e l a t e d c r o s s r e s i s t a n c e (Fujimura, Ishii). Other c h a p t e r s d e s c r i b e b a s i c r e s e a r c h and cooperative i n i t i a t i v e s t h a t w i l l form the b a s i s f o r f u t u r e s u c c e s s e s .


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Acknowledgments The i n i t i a t o r o f t h e symposium on w h i c h t h i s book i s based was Dr. M a u r i c e B. Green. I t s s u c c e s s f u l i m p l e m e n t a t i o n and p u b l i c a t i o n a r e due i n l a r g e p a r t t o h i s e f f o r t s and t h o s e o f Dr. Homer M. LeBaron, b o t h o f whom a l s o made i m p o r t a n t c o n t r i b u tions to t h i s chapter. I n a d d i t i o n , Dr. Thomas M. Brown p r o v i d e d v a l u a b l e a d v i c e on b o t h t o p i c s and p a r t i c i p a n t s f o r t h e symposium. I a l s o acknowledge w i t h g r a t i t u d e t h e debt t h i s c h a p t e r owes t o the e a r l i e r r e v i e w s c i t e d above (5-14), and t o t h e o u t s t a n d i n g c o n t r i b u t i o n s t h a t form t h e r e s t o f t h i s volume. I t i s a pleasure t o e x p r e s s my r e s p e c t t o t h e i r a u t h o r s and e d i t o r s f o r making t h e v a s t r e s i s t a n c e l i t e r a t u r e a c c e s s i b l e t o t h e s c i e n t i f i c community. F i n a l l y , thanks a r e due t o Ms. C h e r y l Shanks and Ms. Robin G i r o u x o f ACS Books f o r s u p p o r t t h r o u g h o u t t h e p u b l i c a t i o n p r o c e s s , and t o Ms. F l o r i n e C l a r k e f o r p r e p a r a t i o n o f t h i s m a n u s c r i p t .

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5. 6. 7. 8.

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