No longer at Ease: Priority effects and niche modification in larval interactions of Aedes albopictus, Aedes aegypti, and Culex pipiens.

Mosquito larvae may compete for resources or space in shared habitats with limited nutrients by resource exploitation or defence or both. In container habitats, the sequence of colonization often dictates community assembly. We examined how arrival order and temporal lags (3 and 7 days) influence the competitive outcomes between invasive Aedes aegypti, Ae. albopictus, and resident Culex pipiens. Studies on the magnitude of priority effects in these systems are lacking. Larvae were added simultaneously and sequentially (after 3 and 7 days) to the dynamics between these mosquito species. Results indicate that simultaneous introduction maximizes competitive stress, resulting in significant mortality and reduced wing length across all species. Conversely, early colonizers gained a distinct fitness advantage; a 3-7-day head start significantly enhanced survival and growth, while late-arriving cohorts were severely suppressed. While Ae. aegypti typically maintained competitive dominance, this advantage diminished when Culex established priority. Results from conditioned-water treatments mirrored live-larval interactions, suggesting that chemical and microbial modifications are primary drivers of these priority effects. Adult behavioural responses of adult mosquitoes to competition was also assessed to determine whether females avoid exposing their offspring to competitive environments when possible. Gravid females exhibited clear discrimination when presented with conspecific-conditioned, heterospecific-conditioned, and dechlorinated water. The general avoidance of heterospecific-conditioned water suggests that chemical cues guide oviposition decisions, potentially functioning as a mechanism to bypass competitive pressures in natural habitats. Understanding these mechanisms is essential for predicting invasion outcomes and for designing vector control strategies that exploit natural competitive asymmetries.