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.