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Love song of the dengue vector mosquito

Male and female mosquitoes match pitch when in the mood

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3:18pm, January 8, 2009
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Mosquitoes use their own kind of eHarmony to find a compatible mate. New research shows that male and female mosquitoes sing duets of matching love songs by vibrating their wings. The annoying recordings of mosquito duets aren’t likely to go platinum, but they give researchers some interesting new ways to think about courtship behavior in insects.

The study, published online January 8 in Science, finds that male and female Aedes aegypti — carriers of dengue and yellow fever — change the pitch of their buzzing to match each other’s harmonics. The results go “way beyond the accepted dogma on hearing in mosquitoes and perhaps indeed in other organisms,” comments Daniel Robert, an expert on insect hearing at the University of Bristol in England. 

A female mosquito’s come-hither buzz, produced by vibrating her wings at a certain rate, is irresistible to males. Scientists have long thought that male mosquitoes could hear just enough sound to locate and home in on a female, says coauthor of the new study Ronald Hoy, of Cornell University.

What’s more, females were thought to be totally deaf. The importance of female behavior in animals has been overlooked until the last few decades, says Hoy. “The assumption was that it’s all about the guys,” he says.

Understanding how mosquitoes really woo one another may lead to new ways to stop their reproduction, which in turn could halt the spread of diseases mosquitoes carry.

A single female mosquito flying through the air produces a complex sound made up of a fundamental tone — which hovers around 400 hertz — and a stack of harmonics. Sometimes called overtones, harmonics are multiples of the fundamental tone. A female mosquito therefore can produce tones of around 400, 800 and 1200 hertz, says Hoy.

In the new experiments, researchers delicately tethered live mosquitoes to the ends of flexible wires, and recorded the tones made by the wings as a male and female mosquito came within a few centimeters of each other. Although the fundamental tones for each mosquito didn’t change very much during a “fly by”— females still produced a fundamental 400-hertz tone and males a 600-hertz tone — each mosquito produced a faint harmonic note, right around 1200 hertz, that was closely in sync.

That these sweet nothings are matched means that the female hears and responds to the presence of the male, and vice versa, shattering the notion that female mosquitoes are inactive bystanders in courtship behavior, the team suggests.  At the same time, 1200 hertz far exceeds the accepted range of male mosquito hearing.

“You’re not going to hear the harmonic until you’re really close. It’s like whispering sweet nothings,” says Hoy. Picking out these loving murmurs is an acoustic feat. “I doubt that humans — except for a few musicians with great, and trained, ears — could do that,” he says.

A 2006 study first suggested that females may have an active role in courtship. That study showed that females of the nonblood feeding mosquito Toxorhynchites brevipalpis match fundamental notes with males, a feat that would be impossible if females were deaf.

This “acoustical interactivity,” as Hoy and colleagues call it, may be an important step for mosquito reproduction.

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