19 Downloaded by UNIV OF CALIFORNIA SANTA BARBARA on March 14, 2018 | https://pubs.acs.org Publication Date: April 26, 1985 | doi: 10.1021/bk-1985-0276.ch019
Detoxification Enzyme Relationships in Arthropods of Differing Feeding Strategies CHRISTOPHER A. MULLIN Pesticide Research Laboratory and Graduate Study Center, Department of Entomology, The Pennsylvania State University, University Park, PA 16802
Detoxification enzymes were compared in 36 arthropod species representing both chewing and sucking herbivores and their natural enemies. Enzymes studied include aldrin epoxidase (MFO), trans-epoxide hydrolase (trans -EH), cis-epoxide hydrolase (cis-EH), and 1-naphthyl acetate esterase. Major selectivities were found for MFO and EH. High MFO and trans-EH activities were consistently associated with herbivory, whereas entomophagous arthropods had a low trans-EH to cis-EH ratio. Phloem-sucking insects were different, exhibiting a low trans-EH to cis-EH ratio. Based on these distinct selectivities, EH may be an appropriate enzyme site for design of a broad-spectrum bioregulator of herbivorous pests that will have little impact on natural enemies.
A r t h r o p o d s i n d i f f e r e n t f e e d i n g n i c h e s tend t o have c o n t r a s t i n g s u s c e p t i b i l i t i e s to p e s t i c i d e s . Hence, l e p i d o p t e r a n l a r v i c i d e s a r e o f t e n c h e m i c a l l y d i s t i n c t from a p h i c i d e s ( 1 - 3 ) , and c o n v e n t i o n a l p e s t i c i d e s w i t h few e x c e p t i o n s e x h i b i t g r e a t e r l e t h a l i t i e s f o r p r e d a t o r s and p a r a s i t e s than t h e h e r b i v o r o u s p e s t s they a r e t a r g e t e d f o r (4) · Knowledge o f t h e d e f e n s i v e s t r a t e g i e s a r t h r o p o d s use t o s e l e c t i v e l y s u r v i v e a t o x i c a n t exposure i s n e c e s s a r y f o r s u c c e s s f u l design of chemical b i o r e g u l a t o r s that a c t to c o n t r o l p e s t p o p u l a t i o n s , b u t have t h e a p p r o p r i a t e s a f e t y f o r n o n t a r g e t species. A l t h o u g h s e q u e s t r a t i o n , p e n e t r a t i o n b a r r i e r s and e x c r e t i o n a r e n o t a b l e f a c t o r s , m e t a b o l i s m and a c t i o n a t t h e t a r g e t s i t e a r e o f g r e a t e r importance i n e x p l a i n i n g t h e s p e c i e s v a r i a t i o n i n s u s c e p t i b i l i t y t o t o x i c a n t s ( 3 ) . G e n e r a l l y , enzymatic d e t o x i f i c a t i o n i s t h e most d i r e c t and dependable way f o r an a n i m a l t o s u r v i v e a t o x i c a n t overexposure. Metabolic transformation of l i p o p h i l i c toxicants including p e s t i c i d e and p l a n t a l l e l o c h e m i c a l s t o e x c r e t a b l e p r o d u c t s u s u a l l y proceeds by a s e r i e s o f enzymatic e v e n t s t o u l t i m a t e l y d e t o x i f y t h e c h e m i c a l . Many o f t h e i n i t i a l r e a c t i o n s c a n g e n e r a t e i n t e r m e d i a t e s
0097-6156/85/0276-O267$06.00/0 © 1985 American Chemical Society
Hedin et al.; Bioregulators for Pest Control ACS Symposium Series; American Chemical Society: Washington, DC, 1985.
Downloaded by UNIV OF CALIFORNIA SANTA BARBARA on March 14, 2018 | https://pubs.acs.org Publication Date: April 26, 1985 | doi: 10.1021/bk-1985-0276.ch019
268
BIOREGULATORS FOR PEST CONTROL
t h a t a r e more t o x i c t h a n the p a r e n t x e n o b i o t i c . I n c l u d e d among t h e s e a r e s e l e c t i v e o x i d a t i o n s c a t a l y z e d by the cytochrome P-450 monooxygenases ( m i x e d - f u n c t i o n o x i d a s e , MFO) e x e m p l i f i e d by d e s u l f u r a t i o n a t the phosphorus bond (P=S t o P=0), t h i o e t h e r o x i d a t i o n s , and e p o x i d a t i o n (5,6) . F o r example, e p o x i d a t i o n o f o l e f i n s and arenes l a r g e l y by MFO can produce r e a c t i v e e p o x i d e s h a r m f u l t o the animal (7,8). The enzyme e p o x i d e h y d r o l a s e (EH) c a t a l y z e s the a d d i t i o n of water to the e p o x i d e , t h e r e b y d e t o x i f y i n g i t t o a more e x c r e t a b l e 1,2-dihydroxy m e t a b o l i t e . Examples of an o l e f i n t o d i o l pathway i n c l u d e the m e t a b o l i s m of a l d r i n , c a r b a r y l , p o l y c y c l i c a r o m a t i c h y d r o c a r b o n s , and the p l a n t t o x i c a n t s r o t e n o n e , p y r e t h r i n s , p r e c o c e n e s , and limonene t o the r e s p e c t i v e t r a n s - d i o l s ( 5 - 1 2 ) . The h i g h c h e m i c a l r e a c t i v i t y of many e p o x i d e s and the l a c k of an e f f e c t i v e i n v i v o i n h i b i t o r o f EH o f t e n n e g a t e s the i s o l a t i o n of e p o x i d e i n t e r m e d i a t e s from b i o l o g i c a l s y s t e m s , and thus many remain p u t a t i v e . Nevertheless, some, such as d i e l d r i n , a r e r e f r a c t o r y t o h y d r a t i o n , and s e r v e as u s e f u l models i n i n v e s t i g a t i o n s of e p o x i d e f o r m i n g and d e g r a d i n g pathways (9). U n d e r s t a n d i n g the b a l a n c e of a c t i v a t i o n and d e t o x i f i c a t i o n enzymes s u c h as e p o x i d a s e r e l a t i v e to EH a v a i l a b l e t o an o r g a n i s m w i l l help d e f i n e i t s a d a p t a b i l i t y to chemical s t r e s s . The well-known s e l e c t i v i t i e s of some organophosphates may be e x p l a i n e d by the b a l a n c e o f e n z y m a t i c e v e n t s . The reduced t o x i c i t y of the i n s e c t i c i d e m a l a t h i o n t o mammals i s l a r g e l y the r e s u l t of r a p i d a c t i v a t i o n by d e s u l f u r a t i o n i n the i n s e c t and the more r a p i d d e t o x i f i c a t o n by c a r b o x y l e s t e r a s e s and g l u t a t h i o n e t r a n s f e r a s e s i n the mammal (3) · D e s i g n o f new p e s t b i o r e g u l a t o r s s h o u l d e x p l o i t enhanced a c t i v a t i o n and d e c r e a s e d d e t o x i f i c a t i o n c a p a b i l i t i e s i n the t a r g e t e d p e s t s . E x p l o r a t i o n of b i o c h e m i c a l bases f o r p e s t i c i d e s e l e c t i v i t i e s between chewing and s u c k i n g h e r b i v o r e s , and n a t u r a l enemies has l a g g e d because of d i f f i c u l t y i n r e a r i n g entomophages and the u s u a l l y i n s u f f i c i e n t biomass a v a i l a b l e f o r enzyme a s s a y . The t y p i c a l l y s m a l l n a t u r a l enemy, e s p e c i a l l y p a r a s i t o i d s , p r e c l u d e s d i s s e c t i o n of s p e c i f i c organs where d e t o x i f i c a t i o n enzymes r e s i d e i n c l u d i n g the m i d g u t , f a t body o r m a l p h i g h i a n t u b u l e s , but r a t h e r n e c e s s i t a t e s use of whole body homogenates which may r e l e a s e f a c t o r s t h a t i m p a i r enzyme measurements ( 1 3 ) . R e g a r d l e s s , more s e n s i t i v e and r a p i d enzyme a s s a y s , and s t a b i l i z i n g a d d i t i v e s i n c l u d i n g a n t i o x i d a n t s and i n h i b i t o r s o f p r o t e i n a s e s and p h e n o l o x i d a s e s now allow the s a t i s f a c t o r y i n v i t r o s t u d y of d e t o x i f i c a t i o n enzymes w i t h i n whole body p r e p a r a t i o n s o f m i c r o a r t h r o p o d s ( 1 3 - 1 5 ) . These t e c h n i q u e s s h o u l d a i d i n u n d e r s t a n d i n g the b i o c h e m i c a l e v e n t s r e s p o n s i ble f o r chemical s e l e c t i v i t i e s . Enzyme A s s o c i a t i o n s w i t h H e r b i v o r e
Status
S e l e c t i v i t i e s t o s y n t h e t i c p e s t i c i d e s may be e x p l a i n e d , i n p a r t , by preadaptations to t o x i c d i e t a r y chemicals. L e a f chewing p e s t s , phloem-sucking p e s t s , and entomophagous n a t u r a l enemies s h o u l d have v e r y d i f f e r e n t e x p o s u r e s to d i e t a r y t o x i c a n t s . Plant defensive c h e m i c a l s a r e thought to be a l l o c a t e d m o s t l y to s p e c i a l i z e d o r g a n e l l e s o r t i s s u e s of e x t e r n a l s t r u c t u r e s , and o n l y a t low loadings
Hedin et al.; Bioregulators for Pest Control ACS Symposium Series; American Chemical Society: Washington, DC, 1985.
Downloaded by UNIV OF CALIFORNIA SANTA BARBARA on March 14, 2018 | https://pubs.acs.org Publication Date: April 26, 1985 | doi: 10.1021/bk-1985-0276.ch019
19.
MULLIN
Detoxification Enzymes in Arthropods
269
i n v a s c u l a r t i s s u e s (16,17). However, phloem l o a d i n g and t r a n s l o c a t i o n of c h e m i c a l s w i t h i n p l a n t s i s p o o r l y u n d e r s t o o d ( 1 8 , 1 9 ) . N e v e r t h e l e s s , chewing h e r b i v o r e s such as l e p i d o p t e r a n l a r v a e and c o l e o p t e r a n s e x p e c t a n t l y consume h i g h e r l o a d i n g s o f p l a n t t o x i c a n t s than phloem-sucking c o u n t e r p a r t s such as a p h i d s . Thus, m e t a b o l i c a d a p t a t i o n s t o t o x i c c h e m i c a l s s h o u l d be b e t t e r d e v e l o p e d i n chew ing r e l a t i v e to sucking h e r b i v o r e s . T h i s i s i n d i c a t e d by the gen e r a l l y higher s u s c e p t i b i l i t y of sucking h e r b i v o r e s to c o n v e n t i o n a l p e s t i c i d e s than chewing h e r b i v o r e s ( 1 - 3 ) . Arthropod p a r a s i t o i d s and p r e d a t o r s , however, a r e u s u a l l y exposed t o p l a n t t o x i c a n t s v i a t h e i r p a s s i v e a c c u m u l a t i o n i n n o n e s s e n t i a l t i s s u e s o f the h e r b i v o r ous h o s t o r p r e y ( 2 0 ) . I t may be e x p e c t e d t h a t c a r n i v o r e s , because of lowered e n c o u n t e r , would l a c k w e l l - d e v e l o p e d detoxification f i t n e s s f o r p l a n t allelochemicals· Comparison of the t o x i c o l o g i c a l b a s e s t h a t a l l o w p e s t i f e r o u s ( i . e . , h e r b i v o r y ) and beneficial ( i . e . , c a r n i v o r y ) a c t i v i t i e s t o concur w i l l a s s i s t our u n d e r s t a n d i n g o f how t o manage a r e a l i s t i c complex o f c r o p a r t h r o p o d s . H e r b i v o r o u s i n s e c t s must contend w i t h t o x i c phytochemicals, many o f which a r e e p o x i d e s o r t h e i r o l e f i n i c p r e c u r s o r s (21-23)· These p h y t o c h e m i c a l s o f t e n e x h i b i t t r a n s - g e o m e t r y , o r a r e h i g h e r s u b s t i t u t e d e p o x i d e s and o l e f i n s , whereas a n i m a l s p r e f e r a b l y b i o synthesize c i s - o l e f i n s (Table I ) . Epoxidation of o l e f i n s , e i t h e r w i t h i n the p l a n t or the consuming i n s e c t , would produce r e a c t i v e e p o x i d e s t h a t may undergo d e t o x i f i c a t i o n by an a p p r o p r i a t e e p o x i d e m e t a b o l i z i n g enzyme. Use of a s u i t a b l e model s u b s t r a t e f o r p l a n t d e r i v e d e p o x i d e s would e x p e d i t e b i o c h e m i c a l a s s o c i a t i o n s between p l a n t s and a n i m a l s . Trans-β - e t h y l s t y r e n e o x i d e i s an e x c e l l e n t s u b s t r a t e f o r s e v e r a l EHs, and mimics the e p o x i d e s known t o o r p o t e n t i a l l y d e r i v e d from p h e n y l p r o p e n o i d s (24) and - b u t e n o i d s (27) o f wide o c c u r r e n c e i n the p l a n t kingdom ( F i g u r e 1 ) . Numerous i n v e s t i g a t i o n s have demonstrated the a s s o c i a t i o n o f an i n s e c t MFO e p o x i d a s e w i t h i n c r e a s e d e n c o u n t e r w i t h p l a n t a l l e l o c h e m i c a l s (11,28)· T h i s cytochrome P-450 dependent a c t i v a t i o n r e a c t i o n i s o b v i o u s l y enhanced i n many h e r b i v o r o u s p e s t s . Hence, i t i s o f i n t e r e s t t o e x p l o r e t h e r o l e o f EH d e t o x i f i c a t i o n i n arthropod herbivory. Table
I.
Propensity
f o r T r a n s - and C i s - O l e f i n B i o s y n t h e s i s i n Animals and P l a n t s Plant Common Fatty acids Cinnamic a c i d s Chalcones, s t i l b e n e s Carotenoids Phenylpropenoids sphingosine i n both
C h e m i c a l group Trans-olefins Examples
Animal Infrequent Pheromones Pros t a g l a n d i n s
Cis-olefins Examples
Common Predominant F a t t y acids i n both
Fumaric a c i d and
a
References
(24-26)
Hedin et al.; Bioregulators for Pest Control ACS Symposium Series; American Chemical Society: Washington, DC, 1985.
Downloaded by UNIV OF CALIFORNIA SANTA BARBARA on March 14, 2018 | https://pubs.acs.org Publication Date: April 26, 1985 | doi: 10.1021/bk-1985-0276.ch019
BIOREGULATORS FOR PEST CONTROL
trons-B-ethyl-3,4-dimethoxystyrene Zingiber caseumunar
trans-6-ethylstyrène
trans-anethole
oxide
anise
trans-asarone
methyl trans-isoeugeno!
sweet flag
carrot
F i g u r e 1. Analogy o f t r a n s - 3 - e t h y l s t y r e n e o x i d e w i t h common p l a n t p h e n y l p r o p e n o i d s and - b u t e n o i d s .
Hedin et al.; Bioregulators for Pest Control ACS Symposium Series; American Chemical Society: Washington, DC, 1985.
Downloaded by UNIV OF CALIFORNIA SANTA BARBARA on March 14, 2018 | https://pubs.acs.org Publication Date: April 26, 1985 | doi: 10.1021/bk-1985-0276.ch019
19.
MULLIN
Detoxification Enzymes in Arthropods
271
Enzyme p r o f i l e s were compared i n a few l e a f chewing and p i e r c i n g - s u c k i n g h e r b i v o r e s , as w e l l as c a r n i v o r o u s a r t h r o p o d s (Table II). A l d r i n epoxidase, t r a n s - g - e t h y l s t y r e n e oxide hydrolase, c i s s t i l b e n e o x i d e h y d r o l a s e , and 1-naphthyl a c e t a t e e s t e r a s e were measured u s i n g e s t a b l i s h e d methods (14,29) · E l e v a t e d e p o x i d a s e was a s s o c i a t e d w i t h h e r b i v o r e s , however the most d i s t i n c t group d i f f e r ence was w i t h t r a n s - E H . Chewing h e r b i v o r e s c o n s i s t e n t l y had h i g h e r t r a n s - E H than c a r n i v o r e s (p
