20 JULY 2006
If there's a noise less romantic than the whine of a mosquito, we don't want to hear it. Fingernails screeching on blackboards, car alarms, even a crooked politician's stump speech have nothing on an earful of flying, whining vampires.
But it's all in your point of view: That whine may make us slap-happy, but we
just learned that it can put a mosquito in the mood for love. In a new study,
two British scientists explored how mosquitoes respond to each other, and found
that opposite sex pairs change their wingbeat to match each other. Because
the whine matches the wingbeat frequency, mosquitoes making the same whine
may well be flying at the same speed.
Guys 'n Dolls: A female flies alone. After about 5 seconds, the male is released (higher pitch). Within one second they adjust to almost perfect synchrony (press button to listen). Courtesy Ian Russell and Gabriella Gibson
Same-sex
pairs, on the other hand, may briefly beat in unison, but they then veer off,
making independent whines, 
and probably flying at different speeds.
Dirty Rotten Scoundrels: Male 1 flies alone. After about five seconds, male 2 is released (hear that brief high-frequency tone?). Male 1 changes his frequency for six seconds, then both frequencies diverge, making one nasty skeeter-symphony (press button to listen). Mosquito-phobes: Crank the volume down! Courtesy Ian Russell and Gabriella Gibson
Let's drop that can of bug repellent and get down to some basics. For 150 years, scientists have known that sound waves vibrate a mosquito's antenna, which activates an attached neuronal gadget called Johnston's organ. The pitch of the whine tells us how fast those flapping wings are driving the little bloodsucker toward that unscratchable patch on the middle of your back...
A Drosophila melanogaster fruit fly shows off Johnston's
organ. Both mosquitoes and fruit flies hear sound with Johnston's organ, which
picks up vibrations from the antenna. Mosquitoes have keen hearing, for bugs. Courtesy
Andrew Jarman, University of Edinburgh
Scientists have long known that males would respond to the whine of another mosquito, but almost nothing was known about the acoustic behavior of females, even though they are almost as sensitive to sound as males. To fill in the blanks, mosquito expert Gabriella Gibson of the Natural Resources Institute at the University of Greenwich at Medway, and University of Sussex neuroscientist Ian Russell eavesdropped on same-sex and opposite-sex pairs of mosquitoes.
When one sex was flying, and heard the other sex, they started to synchronize their "music." When it was the female who started flying, as normally happens in the wild, the man on the make matched her frequency within one second. Some swift suitor! But when the lad flew first, the lass needed about six seconds to match his wingbeat. In both cases, the identical wingbeats lasted at least 15 seconds, presumably long enough for mid-air mating.
A male Toxorhynchites brevipalpis mosquito, flying on a
tether, next to a microphone for recording wing beats. Courtesy
Ian Russell
Making a joyful noise!
Many birds, insects and mammals recognize the opposite sex by sound, but this is the first report of insects responding to each other by changing their tune, said Russell, who studies how animals perceive and respond to sound. The behavior differs from typical animal mating behavior, where a male acts up to impress a female, 
Russell says. "Although
the male may be the one to make the effort to home in on the 'singing' female,
the synchronized sound produced is a dual effort. Each tries to match the frequency
of the other. They both enter into a kind of courtship duet."
Questions remain. First, does the change in wingbeat frequency help amorous mosquitoes fly at the same speed, thus facilitating mating? That tantalizing suggestion remains to be proven, Russell said, as does the exact mechanism of recognition (the change in wingbeat noise signals that recognition has taken place, but it's still unclear how the sexes recognize each other, Russell said).
Second, can this new understanding become a weapon against mosquito-borne diseases like malaria? Russell suggests that mutants could be bred with an auditory processing deficit that interferes with mating, but that is years off.
The next step, he says, is to go to Africa, where these mosquitoes normally live, and see if they behave as they do in the lab.
Slap!
— David Tenenbaum
Bibliography
• Flying in Tune: Sexual Recognition
in the Mosquito, Gabriella Gibson and Ian Russell, Current Biology 16,
1311-1316, July 11, 2006
Related Why Files
• Mosquitoes
• Malaria
• Courtship