Superparasitism acceptance and patch-leaving mechanisms in parasitoids: a comparison between two sympatric wasps

Parasitoids often exploit hosts that have a clumped distribution. To divide their foraging effort between patches, females use encounters with unparasitized hosts as a source of information regarding local host density. Theory predicts that depending on host distribution, ovipositions should either increase (if the distribution is aggregated) or decrease (if the distribution is regular) the females' tendency to remain on the patch. However, patch time allocation theories usually ignore the possibility of superparasitism, even though it can change the predictions. We compared patch exploitation strategies of two related and sympatric Drosophila parasitoids. We investigated, with the Cox model, how females divide their foraging effort between patches of different densities and what proximal leaving mechanism they use. The species differed in the information input they used to adjust their patch time. Ovipositions decreased the patch-leaving tendency of Leptopilina heterotoma, which seldom superparasitized; this is consistent with previous results and with the aggregated distribution of Drosophila larvae. In contrast, no effect of oviposition was found on L. boulardi, which accepted most already parasitized hosts. Rejection of parasitized hosts increased the leaving tendency of L. heterotoma, but had no effect on L. boulardi. These wasps have thus evolved very different patch-leaving rules, possibly in response to differences in their superparasitism behaviour.