UNREWARDING EXPERIENCES AND THEIR EFFECT ON FORAGING IN THE PARASITICWASP LEPTOPILINA-HETEROTOMA (HYMENOPTERA, EUCOILIDAE)

The host-foraging behavior of female entomophagous parasitoids is comm only modified by positive associative learning. Typically, a rewarding experience (e.g., successful oviposition in a host) increases a femal e's foraging effort in a host microhabitat of the type associated with that experience. Less well understood are the effects of unrewarding experiences (i.e., unsuccessful foraging). The influence of unrewardin g experience on microhabitat choice and residence time within a microh abitat was examined for the eucoilid parasitoid, Leptopilina heterotom a, in laboratory and greenhouse assays. As determined previously, fema les which oviposited successfully in either of two microhabitat types (fermenting apple or decaying mushroom) strongly preferred to forage s ubsequently on that microhabitat type. However, failure to find hosts in the formerly rewarding microhabitat caused females to reverse their preference in favor of a novel microhabitat type. The effect, though striking, was transient: within 1-2 h, the original learned preference was nearly fully restored. Similar effects of unrewarding experiences were observed with respect to the length of time spent foraging in a microhabitat. As determined previously, oviposition experience in a pa rticular microhabitat type increased the time spent foraging in a patc h of that microhabitat type. However, failure to find hosts in the pat ch caused the time a wasp spent in the next unoccupied patch of that t ype to decrease to almost nothing. In addition, there was a tendency f or an unrewarding experience on a formerly rewarding microhabitat type to extend the time spent in a patch of a novel type. The function of the observed effects of unrewarding experiences is discussed.