D3366: Thermal immune performance in juveniles and adults of the mosquitoes, Aedes aegypti and Culex pipiens

Temperature creates many physiological challenges and opportunities that can suppress or enhance immune activity in ectotherms. Therefore, climate change is likely to have disparate impacts on immune activity within and among species. We currently know little of immune variation in response to temperature in insects, inhibiting our ability to understand the impact of changing temperatures on the outcome of infection.

To determine if variation in the immune response occurs and whether it may arise from variation in thermal environments and life histories, I compared the thermal performance of the insect immune system between juvenile and adult life stages of Aedes aegypti. I measured melanization intensity and encapsulation layers, as well as the mosquitoes’ ability to clear bacteria and survive fungal exposure over temperatures of 10, 18, 26, and 32°C.

Larval immunity in Ae. aegypti was more constrained at higher temperatures compared to adults. Aedes aegypti larvae exhibited their greatest melanization and encapsulation responses at 26°C and declined thereafter; in contrast, adults melanization plateaued from 26°C to 32°C, and encapsulation plateaued from 18°C to 32°C. Both larvae and adults exhibited the weakest immune responses at 10°C, but larval immunity melanization was strong at 10°C relative to the adults. Adults relied more heavily on encapsulation, whereas larvae produced stronger melanization responses. Overall, this suggests that the immune system responds to the environment in different ways depending on life stage. Understanding this variation will be essential for predicting how insects will survive infection under changing thermal environments.