Neural bases of mosquitoes' responses to visual threats

Despite the associated risks, female mosquitoes have no other choice but to feed on mobile and defensive hosts to acquire proteins and nutrients required to produce progeny. During the time they search and drink our blood, located under the surface of our skin, these female mosquitoes are exposed to the risk of being detected and either hurt or killed by our swats. Their ability to detect and avoid these threats is thus directly related to their fitness and reproductive success. While visually guided escape responses have been extensively analyzed in classical model species such as Drosophila melanogaster, how mosquitoes detect and respond to visual threats has only started to be unraveled. In this context, we combined behavioral, immunohistochemical, and electrophysiological methods to determine how Aedes aegypti females respond to visual threats in both free and tethered flight. Using LED arenas and LCD displays to introduce looming stimuli designed to mimic a swatting hand, we observed that visual threats do not prevent in-flight mosquitoes from landing on a host mimic but trigger an oriented escape response in landed mosquitoes engaged in blood feeding. Investigations into the neural basis of these responses revealed the presence of large descending neurons comparable to the Giant Fiber Neuron system identified in fruit flies. These results will be discussed in the context of mosquitoes’ adaptations to feeding on live and defensive hosts.