Warmer temperature accelerates the aging-dependent decrease of hemocytes in mosquitoes

Mosquitoes acquire pathogens through blood meals, and upon encounter, mosquitoes mount an immune response to eliminate these pathogens. The strength of this response is mediated by immune cells called hemocytes, which exist attached to tissues (sessile hemocytes) or in circulation with the hemolymph (circulating hemocytes). Immune efficacy is reliant on many factors, including environmental temperature and the age of the mosquito. Temperature impacts immunity because mosquitoes are poikilothermic ectotherms, so the environmental temperature predicates their body temperature, which determines immune response intensity. Aging impacts immunity because senescence results in weakened immune prowess. However, the effects of the interaction between temperature and aging are not well characterized. Thus, we aim to uncover the individual and interactive effects of warmer temperatures and aging on the mosquito’s cellular immune response. We hypothesize that warmer temperatures accelerate the rate of immune senescence. To test this, we reared the African malaria mosquito, Anopheles gambiae, at 27℃, 30℃, and 32℃, and quantified the number of hemocytes at 1, 5, 10, and 15 days post-eclosion. We discovered that the number of sessile hemocytes increased with infection and warmer temperature but decreased with aging. Meanwhile, circulating hemocytes decreased with warmer temperature and aging but did not change with infection. Importantly, warmer temperature accelerated the aging-dependent decline in both hemocyte classes, suggesting that immune senescence occurs at a younger age when the temperature is warmer. These findings shed light on the complex interaction between temperature and aging and have direct implications on how mosquitoes fight infection.