Avoid the light to avoid the heat? Thermal and light preferences of Aedes aegypti mosquito larvae

Mosquito-borne pathogens continue to pose a significant health threat worldwide. Efforts to combat mosquito-borne diseases mainly focus on the elimination of either adult mosquitoes or their breeding habitats. A comprehensive understanding of larval physiology and behaviour, particularly in response to light and temperature conditions, might advance the efforts of breeding habitat elimination. This study aimed to investigate the behavioural responses of mosquito larvae to temperature, light and the interaction between these two. The research was performed with Aedes aegypti mosquito larvae, which were tracked for 31 min with an infrared camera in water-filled aluminium trays that were subjected to different temperature and lighting conditions. The larvae exhibited a preference for cooler temperatures in all three gradients (10–20 °C, 20–30 °C, 30–40 °C) under light conditions, aligning with the behaviour of adult mosquitoes. This preference is believed to be an adaptive response to avoid heat stress in their natural breeding habitats. However, in the 20–30 °C gradient without light, the larvae displayed a more even distribution around the point of release. Furthermore, when both temperature and light gradients were present, the larvae initially (until minute 15) demonstrated negative phototaxis. Only later (after 15 min) did they prefer the cooler side. This suggests that Ae. aegypti larvae eventually prioritize thermotaxis. Movement analysis revealed that larval velocity was higher at the initial release site and at higher temperatures. Intriguingly, the larvae were more active during the dark phase, possibly to enhance their exploration and foraging abilities when visual predators are less active. These results highlight the complex interplay of the environmental cues temperature and light in shaping the behaviour of mosquito larvae. • Aedes aegypti larvae prefer low temperatures in permanent light. • In constant dark, larvae prefer a temperature of around 24 °C. • Larvae first show a negative phototaxis but then show a preference for cold. • Larvae move more quickly in the dark than in the light.