Ecology of Infochemical Use by Natural Enemies in a Tritrophic Context

Parasitoids and predators of herbivores have evolved and function within a multitrophic context.Consequently, their physiology and behavior are influenced by elements from other trophic levels such as their herbivore victim (second trophic level) and its plant food (first trophic level) (126).Natural enemies base their foraging decisions on information from these different trophic levels, and chemical information plays an important role.This review is restricted to the ecology of chemical information from the first and second trophic levels.The importance of so-called infochemicals, a subcategory of semiochemicals, in foraging by parasitoids and predators has been well documented (e.g.reviewed in 31, 78, 111,183,185), and we do not intend repeat the details.But because of a lack of testable hypotheses, all this research is conducted rather haphazardly: the total puzzle of infochemical use has not been solved for any natural enemy species.Here we approach the use of infochemicals by natural enemies from an evolutionary and ecological standpoint.Our basic concept is that information from the first and second trophic levels differs in availability and in reliability, a difference that shapes the way infochemicals are used by a species.We generate hypotheses on (a)