Geographic variation in reproductive success of the parasitoid Asobara tabida in larvae of several Drosophila species

Abstract. Asobara tabida is a parasitoid of Drosophila larvae in fermenting substrates. Because it is a widespread species, it may encounter different biotic and abiotic circumstances in various parts of its range. The species composition of the host population varies over the parasitoid's range: D.obscura‐group species (especially D.subobscura) are the main hosts for northwestern and central European parasitoids; D.melanogaster is the main host for southern European parasitoids. D.melanogaster larvae can defend themselves against A.tabida by encapsulating the parasitoid egg, and survival in D.melanogaster is always lower than in D.subobscura. Parasitoids from southern European populations are much better able to survive in D.melanogaster than their northwestern and central European conspecifics; parasitoids from different populations are equally well able to survive in D.subobscura. The lower survival in D.melanogaster may be partly compensated for by the larger size of parasitoids emerging from this host species compared to parasitoids emerging from D.subobscura. Within population groups, larger A.tabida females have more eggs in their ovarioles. Additionally, southern European females have more eggs and less fat than northern and western/central European females. The relationship between size and longevity is ambiguous. It is concluded that parasitoids from different populations are adapted to region‐specific circumstances.