Functional response to host density in a parasitic wasp,with reference to population regulation

1. The functional response to, and preference for, the host density in a parasite were examined experimentally using an icheumon wasp, Exidechthis canescens, and its host Cadra cautella under controlled conditions.
2. Wasps were more active in host-searching at higher than lower host densities. Percent parasitism increased rapidly with initial increments in host density and then tended to increase more slowly at higher host densities. A sigmoid functional response curve is indicated, which implies that the parasite is able to control its host even at low densities.
3. Wasps actively selected areas of high host density in which to concentrate host-searching behavior.
4. Host-searching by E. canescens is stimulated by the odor of the host when present, and by food in which hosts have developed but have been removed.
5. Both the functional response and the host-density preference of the parasite are mediated by its host-searching behavior. This relationship is discussed in the context of population regulation.