Seasonal variation of immature mosquitoes in rice fields and their association with water quality and crop growth stages in a peri‐urban area of Hanoi, Vietnam

Rice agroecosystems are among the most productive mosquito habitats in Asia, but the ways in which crop phenology and urbanisation‐driven environmental changes shape immature mosquito vector populations remain poorly understood. We quantified mosquito larvae and pupae dynamics across two crop seasons in a rice field located in a peri‐urban area of Hanoi, Vietnam, using generalised linear models with appropriate error distributions. A total of 3196 immature mosquitoes representing six species were collected. Overall mosquito abundance was significantly higher in spring than in autumn and peaked during the vegetative stage. Species richness did not vary between seasons but declined significantly at later crop stages. Larval‐stage structure varied with both season and crop phenology. Early instars were more prevalent in spring and during the reproductive stage, whereas late instars dominated in autumn and declined during the ripening stage. The proportion of pupae decreased during the reproductive stage. Among dominant taxa, Culex tritaeniorhynchus and Anopheles barbirostris showed strong seasonal responses, whereas Cx. quinquefasciatus exhibited no significant temporal variation. Environmental drivers differed among species. Culex tritaeniorhynchus was positively associated with water depth, pH and dissolved oxygen, but negatively associated with conductivity. In contrast, Cx. quinquefasciatus was strongly associated with higher conductivity, while An. barbirostris showed negative associations with temperature and conductivity. These findings indicate that mosquito development in rice fields is jointly structured by crop seasonality and agronomic water management, with early crop stages creating favourable conditions for larval proliferation. The dominance of vector species of epidemiological concern underscores the need to integrate phenology‐based habitat management into nuisance and mosquito vector control strategies in Hanoi and similar peri‐urban rice‐growing landscapes.