Mosquito hearing is the most sensitive among arthropods—But is the sound level of a male swarm loud enough to be picked up by the female’s particle-velocity sensor?

Males of many mosquito species aggregate in station-keeping swarms, waiting for the arrival of conspecific females to mate with. We test whether audition could be used by a female to locate male swarms and to assess whether the males are conspecific. The sound level resulting from thousands of wing flaps could be loud enough to be heard at a long range (~1 m) via the antennal flagellum (particle velocity sensor, primarily designed for close-range communication). A mosquito hears a conspecific by adjusting its own wing-beat frequency so that the difference tone between its own and the opposite-sex frequencies falls into a narrow band to which the auditory organ is tuned. Indeed, the antennal flagella produce distortion products resulting in difference tones of the nearby soundscape. Swarmsof males were recorded and played-back to females in a 2-m-sided flight chamber. The natural sounds of the males of two species (Anopheles coluzzii and A. gambiae) and related synthetic sounds were played at different sound levels to individual free-flying A. coluzzii females. The mosquitoes’ responses were investigated by analysing changes in three-dimensional-tracked flight trajectories and wing-beat frequencies. The results show that (1) females do respond to the sound of swarming males, (2) a qualitative difference between female and male behaviour, (3) a quantitative effect of the sound stimulus of conspecific males, and (4) verification of previous results suggesting the importance of the first harmonic of their wing beats in mosquito acoustic communication.