Attracted to the enemy: Aedes aegypti prefers oviposition sites with predator-killed conspecifics

Some mosquito species avoid oviposition in sites harboring aquatic predators. Evolution of this trait may depend on selection via predator-induced mortality. In Brazil larvae of the predator Toxorhynchites theobaldi and Aedes aegypti do not co-occur naturally. Because of this, we predicted that under laboratory conditions, A. aegypti would not avoid oviposition in cups with predator cues (predator alone) and predator-induced mortality cues (predator feeding on prey). To create chemical cues, larvae were held in water and removed after 48h. A single gravid A. aegypti female was added to each bioassay cage and left to oviposit for 48h. Consistent with our prediction, A. aegypti females did not avoid oviposition in predator-cues cups. In contrast, oviposition was significantly greater in predator-induced-mortality-cues cups than in control cups. We hypothesized that predators leave prey partially uneaten, increasing abundances of bacteria upon which Aedes larvae feed, and rendering these containers more attractive for oviposition. We tested this in an experiment using crushed A. aegypti larvae. Significantly more eggs were laid in treatment cups compared to control, but adding antibiotics eliminated this effect. This suggests A. aegypti cannot assess larval predation risk from Toxorhynchites, and because of their attraction to high microbial abundances, are likely to oviposit in containers with Toxorhynchites. Toxorhynchites effects on microbial abundances may enhance biological control by making containers with predators more attractive for A. aegypti oviposition, and increasing the impact of Toxorhynchites on A. aegypti populations.