Harmonic Convergence in the Love Songs of the Dengue Vector Mosquito

Abstract

The familiar buzz of flying mosquitoes is an important mating signal, with the fundamental frequency of the female's flight tone signalling her presence. In the yellow fever and dengue vector, Aedes aegypti, both sexes interact acoustically by shifting their flight tones to match, resulting in a courtship duet. Surprisingly, matching is made not at the fundamental frequency of 400 Hz (female) or 600 Hz (male), but at a shared harmonic of 1200 Hz, which exceeds the previously known upper limit of hearing in mosquitoes. Physiological recordings from Johnston's organ (the mosquito's "ear") reveal sensitivity up to 2000 Hz, consistent with our observed courtship behavior. These findings revise widely accepted limits of acoustic behavior in mosquitoes.Mosquito-borne diseases such as malaria, yellow fever, and dengue continue to afflict millions, even after decades of work to control vector populations. Despite this effort, basic aspects of mosquito biology are not fully understood, including mating behavior, an important target for vector control. We now describe investigations in A. aegypti that require revision of the current understanding of mosquito mating behavior. Since Johnston(1) first suggested in 1855 that mosquitoes could perceive sound, over 14 studies have been published on sound production and hearing in A. aegypti (2-17)( Table S1). The buzz of a flying female mosquito acts as a mating signal, attracting males. Typically, the behaviourally salient frequency component of flight tone is the fundamental frequency of wing beat, between 300-600 Hz depending on species (8). However, mate attraction is not simply a matter of a male passively hearing and homing in on a 400 Hz tone. For example, males and females of the non-blood feeding mosquito, Toxorhynchites brevipalpis, modulate their 300-500 Hz wing beat frequencies to match each other (18). Thus, acoustically-mediated mate attraction involves active modulation by both sexes, creating a duet.We show here that males and females of the dengue and yellow fever vector A. aegypti also modulate their flight tones when brought within a few centimeters of each other. This modulation, however, does not match the fundamental wing beat frequency of around 400 Hz (female) or around 600 Hz (male), but a shared harmonic of around 1200 Hz (Fig 1). Consistent with this, a neurophysiological examination of the ears of A. aegypti, shows response in both males and females up to 2000 Hz (Fig 2). These results are surprising, since over decades of behavioral and physiological studies had concluded that male mosquito ears (antennae and associated Johnston's organ) are tuned to 300-800 Hz and deaf to frequencies above 800 Hz (8,19). The present study also directly addresses the issue of auditory competence in female †To whom correspondence should be addressed. * These authors contributed equally to this workBehavioral and physiological experiments demonstrate intersexual acoustic interactions by the yellow fever and dengue vector mosquito, Aedes aegypti, that call for ...

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