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

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 D. 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.