Predator presence versus predator cues: oviposition trade-offs in Aedes albopictus

Abstract

Predator presence can influence mosquito oviposition decisions through direct and indirect cues, yet most studies have examined indirect chemical cues alone. We evaluated the relative effects of live Gambusia affinis fish (direct cue) versus fish-conditioned water (indirect cue) on oviposition by container breeding mosquitoes (mostly Aedes albopictus) in a field experiment conducted at the University of North Carolina at Greensboro. Paired oviposition cups (treatment and control) were deployed along a transect during three replicate 1-wk sessions for each treatment. Egg numbers were analyzed using paired t-tests, and oviposition responses were quantified using the Oviposition Activity Index (OAI). Live fish significantly deterred oviposition. More eggs were laid in control cups (43.2 ± 5.7) compared to cups containing fish (25.9 ± 8.2; OAI = −0.45). When analyses were restricted to cups in which fish remained present throughout the experimental period, deterrence was even stronger (OAI = −0.63). In contrast, fish-conditioned water significantly increased oviposition relative to aged-water controls (47.5 ± 9.1 vs. 30.2 ± 6.0; OAI = 0.20). These contrasting responses suggest that gravid A. albopictus females discriminate between immediate predation risk and residual environmental cues associated with prior predator presence. We hypothesize that attraction to fish-conditioned water may be mediated by microbially derived volatiles stimulated by fish excretions, whereas avoidance of live fish likely involves visual or mechanical cues. Our findings suggest that oviposition site selection reflects a trade-off between cues indicating a high-quality habitat and offspring survival risk, highlighting the multimodal nature of predator detection in container-breeding mosquitoes.