When a mosquito ingests blood, the phagocytic activity of hemocytes increases with warmer environmental temperature and aging.

Most female mosquitoes feed on blood to gain the nutrients needed for oogenesis, but the process of blood feeding often exposes mosquitoes to pathogens. Blood feeding and infection both activate the hemocytes that drive cellular immune responses, and the efficacy of immune responses like phagocytosis varies with environmental temperature, aging, and their interaction. Here, we quantified the hemocyte-mediated phagocytosis response in the hemocoel of adult female mosquitoes during the digestion of a blood meal and thereafter, focusing on mosquitoes that had been reared at 27 °C, 30 °C or 32 °C, and were 3, 5 or 10 days old at the time of blood feeding. We discovered that, in blood-fed mosquitoes, phagocytic activity generally increases when the temperature is warmer and when the mosquito is older. Moreover, within the first three days after a blood meal, warmer temperature does not accelerate the senescence of the phagocytosis response. Altogether, these findings demonstrate that ingesting blood changes how warmer temperature, aging, and their interaction alters the phagocytic response of hemocytes, which has implications for how mosquitoes respond to infection and survive in their environment.