Geographic variation in host-selection behaviour in the Drosophila parasitoid Leptopilina clavipes

In parasitoid wasps, the process of locating and selecting suitable oviposition sites is under strong selection due to the direct linkage of successful host selection and female fitness. Leptopilina clavipes Hartig (Hymenoptera: Figitidae) is a parasitoid wasp of larvae of several Drosophila species that occurs over Western Europe, where it shows genetic differentiation between populations from northern and southern Europe. It is expected to experience differential selection pressures on both physiological (survival) and behavioural (host selection) components of foraging, because it occurs over a broad geographic range. We investigated whether the genetic differentiation in L. clavipes is linked to differentiation in both the physiological and behavioural components of foraging. We compared survival and host-selection behaviour of two L. clavipes strains, one originating from northwestern Europe and one from southern Europe. In a series of choice experiments, females were offered pairs of larvae from three host species that are present in both regions, but use different breeding substrates: Drosophila phalerata Meigen (fungi), Drosophila subobscura Collin (rotting plant material, fungi, and fermenting fruits), and Drosophila melanogaster Meigen (fermenting fruits) (all Diptera: Drosophilidae). Survival patterns across the three host species were similar for both L. clavipes strains. Host-selection behaviour did differ, where parasitoids from southern Europe accepted all hosts offered, while parasitoids from northwestern Europe were more specialists and accepted hosts breeding in fungi, but were reluctant towards D. melanogaster. This differentiation in host-selection behaviour reflects the genetic differentiation present in European L. clavipes and shows adaptation to local differences in host communities.