To our ears, the buzz of a mosquito is intensely irritating and a sign of itchiness to come, but to theirs, it’s a lover’s serenade. The high-pitched drone of a female is a siren’s song that attracts male mosquitoes. And a new study shows that when the two love-bugs meet, they perform a duet, matching each other’s buzzing frequency with careful precision.
The female Aedes aegypti mosquito (the carrier of both dengue and yellow fever) beats her wings with a fundamental frequency of about 400Hz, producing a pitch just slightly lower than concert A. Males on the other hand, have a fundamental frequency of around 600Hz, about one D above middle C.
Lauren Cator and colleagues from Cornell University discovered the sonic secrets of courting mosquitoes by tethering individuals to pins and moving the females past the males. On two-thirds of these fly-bys, the amorous mosquitoes harmonised. Neither took the lead – instead, both buzzers shifted their flight tones so that the male’s second harmonic (the second multiple of his fundamental frequency) and the female’s third had a mutual frequency of about 1,200 Hz. They synchronised in this way for about 10 seconds.
Lacking ears like ours, mosquitoes hear with their antennae and structures called Johnston’s organs. But for decades, the wisdom of textbooks has said that males are deaf to any frequency over 800Hz and females are completely deaf. Cator disproved that by using miniature electrodes to show that the Johnston’s organs of both sexes produced electrical signals in response to frequencies as high as 2000 Hz.
The duets depended on one partner hearing the other. If they were deafened by removing their antennae, or by gluing the antennae to the Johnston’s organs, nothing happened. But seeing another mosquito wasn’t necessary – individuals were all too happy to match the frequency of an electronically produced tone, even one that is set below or above the insect’s natural flight tone.
Cator suggests that a male mosquito’s ability to match the tone of his partner is the result of sexual selection. Perhaps females can judge the best mates by selecting those who can match their frequencies with the greatest skill. That will need to be tested in future studies but for now, one thing is clear – falling for one song makes the female less likely to fall for another.
Cator found virgin females were about three times more likely to match an electronic tone than those who had already mated. That backs up other research which suggests that Aedes aegypti females aren’t keen to mate again for a fair while after they’ve done it once. Cator even suggests that releasing sterile males could be a way of controlling mosquito populations in the wild – it would lead to fruitless matings that would prevent females from engaging in productive ones later.
Reference: L. J. Cator, B. J. Arthur, L. C. Harrington, R. R. Hoy (2009). Harmonic Convergence in the Love Songs of the Dengue Vector Mosquito Science DOI: 10.1126/science.1166541
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