Parasitoid Foraging from
a Multitrophic Perspective:
Significance for Biological Control
W. Joe Lewis and William Sheehan
The occurrence of a pest within a crop system is an ecological phenomenon that should be treated in an ecological manner. Managed cropping systems, like any other ecological community, are living ecosystems within and among which physical and biological processes are dynamic and interactive. Despite artificialities created by management procedures, many plants, herbivores, predators, pathogens, and weeds that exist within a particular crop have been molded and tightly woven together by natural selection over evolutionary time. This web of relationships is dynamic: each member of a relationship has a repertoire of offensive and defensive maneuvers and countermoves that it can make in response to other members.
An ecologically based approach to pest management recognizes that any external intervention within this system of relationships causes ripples through the system, the net effect of which must be considered in achieving effective control. Further, it recognizes the importance of natural defenses inherent within the cropping system and seeks to harness them as the foundation upon which to add, in a complementary way, other technologies for managing pest problems. Natural enemies of pests and inherent defenses of plants are two of the key components upon which we should build such strategies.
In this chapter, we examine some of what is known about foraging behavior within one group on natural enemies (insect parasitoids) from a multitrophic perspective. We emphasize interactions between the first trophic level (plants) and the third trophic level (parasitoids) because plants provide the context for other interactions and because we believe these interactions have the greatest potential for manipulation in biological control. Interactions within the third trophic level (e.g.,