Microbes increase thermal sensitivity in the mosquito Aedes aegypti, with the potential to change disease distributions

The mosquito <i>Aedes aegypti</i> is the primary vector of many disease-causing viruses, including dengue (DENV), Zika, chikungunya, and yellow fever. As consequences of climate change, we expect an increase in both global mean temperatures and extreme climatic events. When temperatures fluctuate, mosquito vectors will be increasingly exposed to temperatures beyond their upper thermal limits. Here, we examine how DENV infection alters <i>Ae. aegypti</i> thermotolerance by using a high-throughput physiological ‘knockdown’ assay modeled on studies in <i>Drosophila</i>. Such laboratory measures of thermal tolerance have previously been shown to accurately predict an insect’s distribution in the field. We show that DENV infection increases thermal sensitivity, an effect that may ultimately limit the geographic range of the virus. We also show that the endosymbiotic bacterium <i>Wolbachia pipientis</i>, which is currently being released globally as a biological control agent, has a similar impact on thermal sensitivity in <i>Ae. aegypti</i>. Surprisingly, in the coinfected state, <i>Wolbachia</i> did not provide protection against DENV-associated effects on thermal tolerance, nor were the effects of the two infections additive. The latter suggests that the microbes may act by similar means, potentially through activation of shared immune pathways or energetic tradeoffs. Models predicting future ranges of both virus transmission and <i>Wolbachia’s</i> efficacy following field release may wish to consider the effects these microbes have on host survival.