An introduced parasitoid enables host range expansion of a resident parasitoid

Native consumers can behave maladaptively towards invasive species, with evolution of behavioural or physiological traits thought to be the main way out of these 'evolutionary traps'. However, shorter term ecological processes resulting from biological invasions could provide other ways to escape evolutionary traps. Asobara cf. rufescens, a resident (i.e. possibly native or previously introduced) parasitoid of drosophilid fly larvae in North America, can rarely produce offspring on the invasive fruit pest Drosophila suzukii in the laboratory, but often emerges from field-collected D. suzukii. We hypothesized that the successful development of the resident parasitoid in the invasive host in the field is made possible by Leptopilina japonica, a recently introduced parasitoid of D. suzukii. In laboratory experiments, we found that the resident parasitoid had more than 30-fold higher offspring emergence in the invasive host when the recently introduced parasitoid was also present. The resident parasitoid was only able to develop when it parasitized the host after the introduced parasitoid, possibly because the introduced parasitoid destroyed the hosts' cellular immunity. The introduced consumer thus enabled a resident consumer to expand its host range to include the invasive host species, rescuing it from an evolutionary trap.