Emergent acoustic order in arrays of mosquitoes.

The yellow fever mosquito Aedes aegypti forms aerial swarms that serve as mating aggregations [1]. Despite lacking the remarkable collective order of other animal ensembles, such as fish and birds [2], the kinematic properties of these swarms bear the hallmarks of local interaction and global cohesion [3,4]. However, the mechanisms responsible for collective behaviour in mosquitoes are not well understood. Mosquitoes use their antennae as hearing organs to locate and interact with one another via the frequencies of sounds generated by their beating wings [5]. Acoustic detection and recognition are known to mediate copula formation in opposite-sex pairs [6], but have not been investigated in larger groups. By recording the flight tones of multiple, tethered, male Ae. aegypti, we test the hypothesis that acoustic signalling is a determinant of swarm morphology and present the first compelling evidence that flight tone interactions between males drive observed group coherence in the frequency domain. We find that group size critically affects collective and individual acoustic traits: cohesive acoustic behaviours emerge in groups of more than six male mosquitoes, occurring to a greater degree than predicted in the absence of interaction. Importantly, acoustic interactions between multiple males differ from those reported previously for same-sex pairs [7,8]. Our findings enable future research targeting key behavioural and reproductive aspects of the biology of mosquitoes of epidemiological importance.