Native predators may reduce the impact or success of invasive species when native prey are adapted to predation and competing invasive species, lacking history with the predator, lack these adaptations. Container mosquitoes are ideal for testing for these effects of native predators. Water-filled containers are colonized by aquatic invertebrates and dominated by larval mosquitoes. In Midwestern forests, larvae of the native mosquito Aedes triseriatus often co-occur with predatory larvae of another mosquito, Toxorhynchites rutilus. Aedes triseriatus larvae reduce predation risk by reducing movement in response to feeding T. rutilus. Aedes japonicus is an increasingly common invasive container mosquito that competes with A. triseriatus and is prey for T. rutilus. We tested the hypothesis that native A. triseriatus are better adapted to this predator than are invasive A. japonicus. At a forested site, we filled two sizes of experimental containers with water and leaf detritus. After 7 weeks of colonization, we removed all T. rutilus from containers and stocked half with second instar T. rutilus at a density of 1/3.5 L and left half as predator-free controls. Every 3 d we removed eggs and extra larvae of T. rutilus. We sampled larvae, pupae, and Aedes oviposition every 12 days.
Results/Conclusions
Stocking and removal of T. rutilus established significantly different levels of predation. Repeated measures ANOVA on abundance/L of A. triseriatus yielded significant effects of size and size-sample period, but not of predation or its interactions. In contrast, abundance/L of A. japonicus was significantly affected by predation, sample, and predation-sample. Aedes triseriatus abundance/L was greater in small containers and decreased over three sample periods. Aedes japonicus abundance/L was greater in the absence of predation, and this difference increased in later samples. Thus, predation shaped this community by reducing A. japonicus while having no effect on A. triseriatus. Pupation success of both species was reduced by predation, but this effect was greater for A. japonicus. Predator effects on abundances were not products of predator avoidance by ovipositing females, as there were no predator effects on eggs laid for either Aedes. Observed effects of predation result from differential success of developing larvae due to the greater lethal effect of T. rutilus on A. japonicus than on A. triseriatus. Thus the native species is better adapted to cooccur with this predator and, more generally, native predators have the potential to limit success and impact of invasive species.