Physiological and environmental factors affecting thermal tolerance in the major malaria vector Anopheles arabiensis (Diptera: Culicidae).

Thermal tolerance is a key determinant of mosquito survival and vectorial capacity under rising global temperatures. Understanding how physiological and environmental factors influence heat tolerance is therefore essential for predicting the impacts of climate change on malaria transmission. Anopheles arabiensis is a major malaria vector in Southern Africa. This species is difficult to control due to its plastic behaviour. This species is typically found in hot, arid areas, and its thermal tolerance may play a role in its capacity to invade new regions, particularly in the context of climate change. This study investigated the effects of humidity, blood-feeding status, age, sex, and strain on the thermal tolerance of Anopheles arabiensis. Temperature knockdown assays were conducted in which adult male and female mosquitoes of different strains and ages were exposed to a sublethal heat stress at 41 °C for 5 hours under controlled-humidity conditions. This is a proxy for resilience under stressful conditions. Females from all strains were more heat-tolerant than males in the 5-hour heat shock assays. In adult females, heat tolerance decreases with age, but this can be rescued by the provision of multiple blood meals. Crucially, insecticide resistant An. arabiensis had a distinct advantage under these conditions. These findings suggest that An. arabiensis is remarkably adaptable to heat stressed conditions with insecticide resistant females being particularly suited for conditions of current climatic conditions. This could have important implications for mosquito population dynamics and malaria risk in a warming climate.