Asymmetric oviposition behaviour between Drosophila suzukii and Drosophila subpulchrella suggests competition for the shared niche in their native range

Abstract Release from competitors is one of the mechanisms ascribed to the ecological success of invasive species outside their native range (competitive release hypothesis). However, studies describing the natural competitors of invasive species in their homeland are limited. Drosophila suzukii , the spotted‐wing drosophila, is an invasive pest of small fruits expanding its range worldwide, whereas Drosophila subpulchrella , the most closely related species to D. suzukii , remains endemic to the native range of D. suzukii . D. subpulchrella is inferior to D. suzukii in terms of the host usage capability, and it has not been considered as a major competitor of D. suzukii . This study examined the interaction between the two species in egg‐laying behaviour. A field survey revealed that 11% of wild berries were co‐infected by both species. In the laboratory experiments, D. suzukii avoided oviposition substrates that had already been oviposited by either conspecific or D. subpulchrella females, whereas D. subpulchrella did not show any preference/avoidance toward the substrates oviposited by either species. This asymmetric interaction indicates that D. subpulchrella may have a negative effect on the D. suzukii propagation as a niche‐sharing competitor in their homeland, raising a possibility that the release from competition with D. subpulchrella helped the expansion of D. suzukii populations in invaded areas.