The realized host specificity of Leptopilina japonica and Ganaspis kimorum, adventive larval parasitoids of the invasive Drosophila suzukii in Western Canada

Abstract

The non-native larval parasitoid wasps Leptopilina japonica and Ganaspis kimorum (Hymenoptera: Figitidae), which attack larvae of the invasive pest Drosophila suzukii (Matsumura) (Diptera: Drosophilidae), were unintentionally introduced to the Pacific Northwest of North America between 10 and 15 years ago, and are now well established. Previous laboratory studies conducted to assess the ecological risk of classical biological control introductions suggested that G. kimorum is highly host-specific, whereas L. japonica can develop in several other drosophilid species. Information on realized host use of the parasitoids under field conditions in the context of host-parasitoid food webs in their non-native range is limited. A two-year field study in coastal British Columbia, Canada was conducted, using complementary sampling methods to document host–parasitoid associations and quantify parasitoid specificity with respect to drosophilid communities inhabiting ripe and rotting fruit. Consistent with the previous laboratory findings, G. kimorum was reared exclusively from D. suzukii, while L. japonica emerged primarily from D. suzukii but also from D. melanogaster and, less frequently, from members of the D. obscura species group. Leptopilina japonica shared some host species with the resident parasitoid species L. heterotoma and Asobara cf. rufescens. A particularly striking result was the extent to which almost all drosophilid and parasitoid taxa in this study’s host–parasitoid trophic webs were non-native, complicating the interpretation of ‘nontarget’ ecological effects of L. japonica. These results provide field-based evidence of realized host use by these two non-native larval parasitoids of D. suzukii that can inform their future use in classical and augmentative biological control programs.