Mechanisms of tritrophic effects of plant chemistry on a parasitoid

North Dakota State University Fargo, Fargo ND

Investigators

Abstract

Mechanisms of tritrophic effects of plant chemistry on a parasitoid Paul Ode1 and May Berenbaum2 1North Dakota State University 2University of Illinois at Urbana-Champaign Plant chemistry is well known to have impacts not only on herbivores, but also on natural enemies of these herbivores. While the effects of plant chemistry on host finding and acceptance behavior of natural enemies is well studied in many systems, comparatively little is known about effects of plant chemistry on other fitness correlates and how natural enemies are able to cope with negative effects of plant chemistry. The parasitic wasp, Copidosoma sosares, is the predominant natural enemy in a system where the selective interactions between plant and herbivore have been particularly well studied. Furanocoumarin production by wild parsnip plants, Pastinaca sativa, selects for detoxification capabilities of the parsnip webworm, Depressaria pastinacella, a specialist herbivore of the wild parsnip. In turn, herbivory by the webworms selects for furanocoumarin-based resistance by wild parsnips. This tritrophic system is native to Europe and has been introduced to western North America; wild parsnips and parsnip webworms are found throughout Midwestern North America, but are effectively parasitoid-free. The central goal of this project is to examine the impacts of wild parsnip furanocoumarins on growth and reproduction of Copidosoma sosares. Furanocoumarin profiles of parsnip plants and their correlation with C. sosares fitness measures in western US populations will be documented. Laboratory studies, manipulating xanthotoxin concentrations in artificial diets, will directly examine the effect of furanocoumarins on C. sosares fitness measures. Other experiments will examine levels of furanocoumarins encountered by C. sosares in their webworm hosts as well as their ability to detoxify any encountered furanocoumarins. Finally, the effects of furanocoumarin variation on reproductive decisions made by C. sosares will be examined. The existence of relatively parasitoid free populations in the Midwestern US and heavily parasitized European and western US populations allows comparison of parasitoid effects on webworm detoxification abilities as well as plant chemistry. Studying the physiological effects of host plant chemistry on natural enemies will allow for a more complete understanding of how trophic relationships function.