Prevalence of exotic frugivorous Drosophila species, D. simulans and D. immigrans (Diptera: Drosophilidae), and its effects on local parasitoids in Sapporo, northern Japan

Abstract

The prevalence of exotic species has a variety of effects on native biological communities. To understand the effect of exotic species on a local Drosophila–parasitoid community, I investigated associations of native and exotic frugivorous Drosophila species (Diptera: Drosophilidae) with local parasitoids in Sapporo, northern Japan. In this survey, two exotic species, D. simulans Sturtevant and D. immigrans Sturtevant, accounted for approximately 88 % of Drosophila individuals that emerged from banana bait; two native species, D. auraria Peng and D. biauraria Bock & Wheeler, accounted for approximately 10 %. Seven larval parasitoid species were recorded as emerging from Drosophila larvae occurring in banana bait; six of these were examined for host use in laboratory experiments. Drosophila simulans was favored as host by four larval parasitoids, but D. immigrans was not favored by most of the larval parasitoids. Nevertheless, more than one-third of parasitoid individuals emerged from D. immigrans in the field study, probably because of its high abundance. Thus, exotic species are assumed to affect the abundance and distributions of native parasitoid species. In this study it was not clear whether the parasitoid species mediate the effects of exotic Drosophila species on native Drosophila species, because the incidence of parasitism was usually low.