Thermal fertility limits reveal underestimated climatic suitability for Aedes aegypti in temperate regions

Predicting species distributions under climate change typically relies on thermal limits for survival. However, recent evidence suggests that sublethal temperatures that reduce fertility can constrain distributions more strongly than temperatures causing mortality alone. Despite the importance of mosquitoes as vectors of human disease, thermal fertility limits remain largely uncharacterized in these insects. Here, we show that fertility in Aedes aegypti is highly sensitive to thermal stress and exhibits distinct sex-specific responses. Adult males were more vulnerable to both heat and cold exposure than females. At 38{degrees}C, survival remained high in both sexes despite significant reproductive impairment, indicating that sterility can occur independently of mortality. Similarly, exposure to 2{degrees}C induced male sterility whereas females maintained reproductive function. Morphological analyses of reproductive organs showed temperature-associated damage consistent with the observed fertility loss. Incorporating these fertility thresholds into ecological niche models generated different predictions of climatic suitability compared with models based solely on lethal temperature limits. Our findings demonstrate that sublethal effects on reproduction can substantially influence estimates of mosquito climatic suitability and highlight the importance of incorporating fertility based thermal limits into projections of vector distributions and disease risk under future climate change.