Fluctuating warm and humid conditions differentially impact immunity and development in the malaria vector Anopheles stephensi

A variety of environmental factors including temperature and humidity influence mosquito physiology and behavior. However, their direct impact on innate immunity, the core mosquito defense system against pathogen infection, remains insufficiently understood. This is particularly important as climate change is likely already altering mosquito distribution. A key limitation in most mosquito studies is the use of unrealistic static temperature and humidity settings which fail to reflect natural environmental changes. To address this, we employed a novel approach, exposing Anopheles stephensi from egg to adult to diurnal fluctuations (+4°C and +10% relative humidity above the baseline). We then investigated the impact of these elevated fluctuating conditions on innate immune gene expression, development, and adult longevity. We show that realistic elevated temperature and humidity fluctuations prime basal immune responses and accelerate pre-adult development without reducing adult lifespan. Bacterial infections under these elevated fluctuating conditions lead to a complex reprogramming of mosquito innate immunity and enhanced survival of both larvae and adults. Furthermore, fluctuating elevated temperature and humidity alter the transcriptional activity of key promoters widely used to express transgenes in genetically modified mosquitoes, highlighting the potential environmental sensitivity of these malaria control strategies. These results suggest that while elevated conditions-driven immune priming could initially decrease A. stephensi's vectorial capacity, the observed post-bacterial challenge immune suppression could enhance susceptibility to Plasmodium, with potential significant implications for vector competence and malaria transmission. Our study findings highlight the need to incorporate realistic environmental variability in mosquito research to accurately predict the impact of climate on disease transmission.