13 Nutrient-Allelochemical Interactions in Host Plant Resistance Downloaded by UNIV OF MASSACHUSETTS AMHERST on May 22, 2018 | https://pubs.acs.org Publication Date: January 20, 1983 | doi: 10.1021/bk-1983-0208.ch013
JOHN C. REESE
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University of Delaware, Department of Entomology and Applied Ecology, Newark, DE 19711 Once an i n s e c t has l o c a t e d a p l a n t , the p l a n t must be capable o f supporting growth, development, and r e p r o d u c t i o n , if the p l a n t is t o serve as a host. The s u r v i v a l o f plants, however, is due in part to t h e i r defensive s t r a t e g i e s . Evidence is presented supporting the hypothesis that even susc e p t i b l e p l a n t s are well-defended. Black c u t worm larvae fed Pioneer 3368A corn seedlings grew t o a weight o f only 8.1% that of l a r v a e fed an artificial d i e t . Some o f the ability to inhibit growth can be e x t r a c t e d out of the p l a n t and incorporated i n t o the artificial diet demonstrating a chemical component, but p h y s i c a l and morphological f a c t o r s appear t o play an important r o l e too. Data is presented indicating that neonate l a r v a e are f a r more s e n s i t i v e t o the d e l e t e r i o u s e f f e c t s o f the seedlings than l a r v a e a few days o l d . Neonate l a r v a e are a l s o s e n s i t i v e to h a n d l i n g , and using eggs i n s t e a d of l a r v a e t o i n f e s t p l a n t s or i n o c u l a t e d i e t seems a d v i s a b l e . "As greater understanding of i n s e c t and p l a n t b i o l o g y , chemistry, and ecology i s a t t a i n e d , we w i l l be able to approach the goal of developing economic p l a n t s that are d e l i b e r a t e l y and f o r e s i g h t e d l y designed to be i n s e c t r e s i s t a n t " ( 1 ) . One of the more i n t e r e s t i n g , and perhaps more poorly understood, areas o f "— i n s e c t and p l a n t b i o l o g y , chemistry, and ecology — , " i s the study of the i n t e r a c t i o n s between a l l e l o c h e m i c s and n u t r i e n t s . A s u i t a b l e host p l a n t must be capable o f supporting growth, development, and r e p r o d u c t i o n , i f the p l a n t i s t o serve as a host. The feeding i n s e c t must i n g e s t food " . . . t h a t not only meets i t s n u t r i t i o n a l requirements, but i s a l s o capable o f being a s s i m i l a t e d and converted i n t o the energy and s t r u c t u r a l substances f o r normal 1
Current address, Department of Entomology, Kansas State University, Manhattan, KS 66506 0097-6156/83/0208-0231$06.00/0 ©
1983 American Chemical Society
Hedin; Plant Resistance to Insects ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
232
PLANT RESISTANCE TO INSECTS
Downloaded by UNIV OF MASSACHUSETTS AMHERST on May 22, 2018 | https://pubs.acs.org Publication Date: January 20, 1983 | doi: 10.1021/bk-1983-0208.ch013
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a c t i v i t y and development (2_ ,3) . Thus, the concept of i n s e c t d i e t e t i c s i n c l u d e s a good d e a l more than n u t r i t i o n i n the narrow sense; feeding behavior, n u t r i t i o n , and p o s t - i n g e s t i v e e f f e c t s are a l s o p a r t of i n s e c t d i e t e t i c s . The i n t e r a c t i o n s between n u t r i e n t s and a l l e l o c h e m i c s a t the b e h a v i o r a l , n u t r i t i o n a l , and p o s t - i n g e s t i v e l e v e l s may be very important parts o f the mechanisms u n d e r l y i n g the d e l e t e r i o u s e f f e c t s of p l a n t s on i n s e c t growth and development. I propose that these d e l e t e r i o u s e f f e c t s are probably not confined j u s t t o non-hosts o r t o h i g h l y r e s i s t a n t crop v a r i e t i e s , but may be the r u l e ; i f a p l a n t were t r u l y undefended against h e r b i v o r e and pathogen a t t a c k , i t would i n a l l l i k e l i h o o d not s u r v i v e long enough t o reproduce o r produce a crop. Defense of S u s c e p t i b l e P l a n t s The very s u r v i v a l o f p l a n t s through e v o l u t i o n a r y time i s "... due l a r g e l y t o t h e i r own defensive s t r a t e g i e s ..." ( 4 ) . Most researchers probably accept t h i s concept, and yet the pref e r r e d host p l a n t o f an i n s e c t s p e c i e s , o r a crop that i s decimated by a p e s t , i s u s u a l l y thought of as being q u i t e s u s c e p t i b l e and r a t h e r poorly defended against i n s e c t a t t a c k . I have s t a r t e d t e s t i n g the hypothesis that even the most s u s c e p t i b l e p l a n t s are i n f a c t remarkably w e l l defended against i n s e c t a t t a c k when compared t o an a r t i f i c i a l d i e t c o n t a i n i n g low concentrations of defensive compounds, and having no morphological means of defense. A few species of i n s e c t s , i n f a c t , have already been observed t o have greater f e c u n d i t y and growth on a r t i f i c i a l d i e t s , than on p r e f e r r e d host p l a n t s 05, 6^, 7 ) . While working a t the USDA Western Regional Research Center i n C a l i f o r n i a w i t h A. C. Waiss, J r . , I placed H e l i o t h i s zea l a r v a e on a glanded c o t t o n v a r i e t y , a glandless v a r i e t y (presumably susc e p t i b l e t o bollworm l a r v a e ) , and on a r t i f i c i a l d i e t . Even the weight of the glandless cotton group of l a r v a e was only 25.1% o f the c o n t r o l s on a r t i f i c i a l d i e t , i n d i c a t i n g that even the supposedly s u s c e p t i b l e p l a n t was chemically and/or m o r p h o l o g i c a l l y q u i t e capable o f reducing i n s e c t growth. Black cutworms ( A g r o t i s i p s i l o n ) were fed Pioneer 3368A corn seedlings (not known t o be r e s i s t a n t ) and a r t i f i c i a l d i e t (8) (Table I ) . By the s i x t h day the weight g a i n of l a r v a e fed seedl i n g s was a s m a l l f r a c t i o n of that f o r l a r v a e reared on d i e t . Even though b l a c k cutworms can be severe pests of corn s e e d l i n g s , t h e i r growth i s d r a m a t i c a l l y reduced by them. The a r t i f i c i a l d i e t may have been a r i c h e r source o f n u t r i e n t s than corn s e e d l i n g s . Therefore, I had samples o f d i e t and s e e d l i n g s analyzed f o r n i t r o gen content (as one o v e r a l l measure of n u t r i t i o n a l q u a l i t y ) a t the U n i v e r s i t y of Delaware S o i l Chemistry Laboratory. The a r t i f i c i a l d i e t was a c t u a l l y much lower i n n i t r o g e n than the s e e d l i n g s . Amino a c i d a n a l y s i s showed no s i g n i f i c a n t d i f f e r e n c e s between corn s e e d l i n g s and the a r t i f i c i a l d i e t .
Hedin; Plant Resistance to Insects ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
13.
REESE
Table I .
Nutrient-Allelochemical
233
Interactions
E f f e c t s of Pioneer 3368A corn seedlings and a r t i f i c i a l d i e t (8) on mean weights of black cutworm l a r v a e . Mean L a r v a l Weights (mg) + SD
Downloaded by UNIV OF MASSACHUSETTS AMHERST on May 22, 2018 | https://pubs.acs.org Publication Date: January 20, 1983 | doi: 10.1021/bk-1983-0208.ch013
L a r v a l Age (Days)
Reared on P l a n t s
Reared on D i e t
% of C o n t r o l (Diet)
0.8 + 0.2
37.5% ***
2
0.3 + 0.1
3
0.4 + 0.2
2.4 + 1.2
16.7% ***
4
0.6 + 0.2
4.2 + 2.6
14.3% ***
5
1.0 + 0.5
11.7 + 5.3
8.5% ***
6
1.7 + 1.2
21.1 + 4.6
8.1% ***
*** i n d i c a t e s s t a t i s t i c a l s i g n i f i c a n c e between p l a n t - and d i e t reared l a r v a e a t P
