The effect of competition on oviposition decisions of Leptopilina heterotoma (Hymenoptera: Eucoilidae)
1995
Visser, M.E.
Prey selection models in which a patch is depleted by a number of foragers predict that the less profitable prey are rejected early in the foraging bout, but accepted later on. Such behaviour would lead to partial preferences: certain prey types are sometimes rejected and sometimes accepted (eaten), even within the same foraging bout. In the absence of competition, however, parasitoids should show no such switch in behaviour. This prediction was tested using the insect parasitoid Leptopilina heterotoma (Hymenoptera: Eucoilidae) searching a patch containing unparasitized and parasitized (less profitable) hosts. In the experiments, the degree of competition was varied by (1) having either a single parasitoid or two parasitoids simultaneously searching on the patch, and (2) keeping parasitoids either alone or together with conspecifics before the experiment. For a given patch quality (expressed as the average quality of the five previously encountered hosts), parasitoids accepted parasitized hosts more often when they searched a patch alone than when there were competitors present. Competition clearly influenced oviposition decisions. The predicted switch in behaviour was observed in the presence of competition, and a much less pronounced change in the absence of it. Keeping parasitoids alone or together before the experiment did influence the oviposition decisions but in the opposite way to that predicted: the latter accepted parasitized hosts more readily at high patch quality than the former. Finally, it was shown that the parasitoids are able to distinguish between the four types of host (unparasitized, once parasitized by a conspecific, once parasitized by the female herself and twice parasitized).
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