Sugar intake interacts with temperature to influence reproduction and immunity in adult Culex pipiens mosquitoes

Abstract

Disease transmission by insect vectors will depend on integrated physiological responses to interacting environmental variables. We explored how interactions between temperature and sucrose concentration affected immunity and fecundity, two variables that contribute to vectorial capacity, in Culex pipiens Linnaeus, 1758 mosquitoes. We provided female C. pipiens with either 2% or 20% sucrose and exposed them to low (22 °C), moderate (25 °C), or high (30 °C) temperatures for 8 days. We then measured the strength of the melanization response in one subpopulation of females and the number of eggs laid as a measure of fecundity in another subpopulation. Temperature interacted with diet to weaken immunity under 2% sucrose at 22 and 25 °C. This effect disappeared at 30 °C, suggesting that high temperatures allowed mosquitoes to compensate for the effects of decreased sucrose. Conversely, increasing temperature increased egg production on a diet of 20% sucrose, but heat exposure on a diet of 2% sucrose decreased fecundity. Overall, we suggest that heat exposure requires investment in thermal protection, which may prompt reconfiguration of the immune system and (or) decreased investment in reproduction. Thus, our understanding of the effects of climate change rest on which physiological system we measure and under which combinations of stressors.

Nutritional stress compromises mosquito fitness and antiviral immunity, while enhancing dengue virus infection susceptibility

“…Conceivably, the diminished reserves available under nutritional stress conditions could constrain immune gene expression in our study. This observation resonates with previous research where sugar feeding or higher sugar solution concentrations enhanced mosquito immune responses compared to non-sugar feeding 33 , 71 , 72 . Beyond immune gene expression, inadequate carbohydrate supplies may also translate into a decreased expression of reactive oxygen species (ROS) genes 34 , integral to mosquito pathogen defense 26 .…”

Sugar restriction and blood ingestion shape divergent immune defense trajectories in the mosquito Aedes aegypti

“…Alternatively, but not mutually exclusively, a lower concentration of dietary sucrose may directly or indirectly affect signaling of the mosquito’s immune pathways, thereby inhibiting resistance mechanisms such as melanization, AMP production, and/or hemocyte activity. Higher dietary sugar levels are associated with a stronger melanization response in mosquitoes 31 – 33 , which may initially appear antithetical to our results. However, E. coli is preferentially phagocytized rather than melanized by mosquitoes 34 – 36 , suggesting that any reduction in melanization that may have occurred in the 1% sucrose treatment is unlikely to impact infection outcomes in our system.…”

Sugar restriction and blood ingestion shape divergent immune defense trajectories in the mosquitoAedes aegypti

“…Alternatively, but not mutually exclusively, a lower concentration of dietary sucrose may directly or indirectly affect signaling of the mosquito's immune pathways, thereby inhibiting resistance mechanisms such as melanization, AMP production, and/or hemocyte activity. Higher dietary sugar levels are associated with a stronger melanization response in mosquitoes (32)(33)(34), which may initially appear antithetical to our results. However, E. coli is preferentially phagocytized rather than melanized by mosquitoes (35)(36)(37), suggesting that any reduction in melanization that may have occurred in the 1% sucrose treatment is unlikely to impact infection outcomes in our system.…”