January 8, 2009

Mosquitoes Sync Wing Movements as Mating Signal

New research from Cornell University finds that Aedes aegypti mosquitoes, the kind that spread diseases such as dengue and yellow fever, change their wing vibrations as a mating symbol.

Ronald R. Hoy, who authored a report about the study, said the discovery could pave the way to better methods of controlling mosquitoes.  

Indeed, one such way to control mosquitoes is by releasing sterile males to prevent reproduction.  By monitoring their mating signals, researchers would have a way to determine if the sterile males can carry out courtship with females, Hoy explained.

"We don't want to be releasing duds out there, we want to release sterile studs," Hoy, who studies hearing in insects, said during an interview with the Associated Press.

This is because once mated, female mosquitoes are less likely to mate again.   Therefore, if the initial mating is with a sterile male, no offspring would be produced.

"By studying these flight tone signals, we may be able to determine what kind of information males and females consider important when choosing a mate," said Cornell graduate student Lauren Cator, a co-author of the report.

Hoy said scientists knew the buzzing helped males identify female mosquitoes, but the researchers wondered precisely what the insects could hear.   Some mosquitoes match their wing beats when courting, so the researchers decided to see whether this held true for the Aedes aegypti by exposing tethered males and females to one another, he said.

They discovered that while the mosquitoes did indeed alter their wing beats, they did not change them to match one another.  Female mosquitoes typically have a frequency of about 400 beats per second, or hertz, whereas the males use a frequency of roughly 600 hertz, Hoy said.
Once the male and female mosquitoes encountered one another, they both adjusted their frequency until there was a harmonic of about 1200 vibrations per second -- an overtone of both frequencies.

The researchers were surprised that the insects could even sense that overtone.

"Who knew they could sense 1200 hertz," Hoy remarked.

It turns out the insects interact at frequencies they were not previously believed to be capable of hearing.   In fact, until now there was a broad consensus that female mosquitoes were deaf.

To confirm their results, the team implanted electrodes in mosquitoes' Johnston organ, used for hearing, and found the insects could detect frequencies of up to 2000 hertz.

It turns out that even people can hear the mosquitoes' mating song.

"It sounds like the worst ever case of ringing in the ears," said Hoy.




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