Diurnal and nocturnal mosquitoes escape looming threats using distinct flight strategies

Flying insects have evolved the ability to evade looming objects such as predators and swatting hands. This is particularly relevant for blood-feeding insects like mosquitoes that routinely need to evade defensive actions of their blood-hosts. To minimize the chance of being swatted, a mosquito can use two distinct strategies: continuously exhibit an unpredictable flight path or maximize its escape manoeuvrability. We studied how baseline flight unpredictability and escape manoeuvrability affects the escape performance of day-active and night-active mosquitoes (Aedes aegypti and Anopheles coluzzii, respectively). We used a multi-camera high-speed videography system to track how freely flying mosquitoes respond to an event-triggered rapidly approaching mechanical swatter, in four light conditions ranging from pitch darkness to overcast daylight. Results show that both species exhibit enhanced escape performance in their respective natural light condition (daylight for Aedes and dark for Anopheles). To achieve this, they show strikingly different behaviours. The enhanced escape performance of Anopheles at night is explained by their baseline unpredictable erratic flight behaviour, whereas the increased escape performance of Aedes in overcast daylight is due to their enhanced escape manoeuvres. This shows that both day and night active mosquitoes modify their flight behaviour in function of light intensity such that their escape performance is maximum in their natural blood-feeding light conditions, when these defensive actions by their blood-hosts occur most. Because Aedes and Anopheles mosquitoes are major vectors of several deadly human diseases, this knowledge can be used to optimize vector control methods for these specific species.