Jan. 8, 2009 -- The soft duet of lovers crooning to each other in perfect harmony is partly responsible for the scourges of dengue and yellow fever, according to new research, which finds that mosquitoes sing to each other to determine mating.
"We think that females could use harmonic matching as a fitness measure for the males," said Ron Hoy, a professor at Cornell University and co-author of the study that appears today in Science. The new research opens a new avenue for public health officials to control disease-spreading populations of mosquitoes.
It's no secret the mosquitoes have a characteristic buzz. It's one of the few warning signs humans have that a winged bloodsucker is about feast on them. For years scientists thought that the buzz was merely an artifact of a mosquito's beating wings, and didn't even think that mosquitoes could hear it.
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Each sex has its own distinctive range. Heavier females beat their wings at about 400 hertz. Lighter weight males beat their wings at about 600 hertz. To humans, it all sounds like a steady buzz. To mosquitoes however, the notes inside that buzz can range all the way up to 1,800 hertz.
Mosquitoes can hear each other from roughly one meter (3.3 feet) away. As a male approaches a female they begin a flying musical number, as the female singes a diddy and then waits for the male to replicate it in harmony. If he fails to accurately reproduce the sound, the female flies away. If she is satisfied with his love song, she mates with him.
To discover this, scientists super-glued male mosquitoes to a pin and listened as females flew around them. The Cornell University scientists used Aedes aegypti, the mosquito that transmits diseases such as yellow fever and dengue fever.
Each species of mosquito has its own song, explained Gabriella Gibson, a mosquito expert at the University of Greenwich who studies the love songs of the Anopheles mosquito, which can transmit malaria and other diseases. By listening in on the songs that mosquitoes sing to each other scientists could determine which species of mosquitoes are in a storm.
"The discovery of this new form of auditory-motor interaction is so novel, it will open up a whole new area of basic research, covering the range of disciplines from neurophysiology to the behavioral ecology of mating strategies," said Gibson.
The research could also help control mosquito populations. One big hope for scientists and public health officials is to create sterile males in the lab, which would then be released into the wild to mate with disease-carrying females.
The problem with that plan is that in making the males impotent, something else might be broken in the males that would make females not want to mate with them, thus defeating the purpose of the experiment. But now scientists could listen to mosquito songs and readily tell if the engineered males were as successful as their wild counterparts at mating with females.
"This could be a great way to assess the sexiness of transgenic mosquitoes," said Laura Harrington of Cornell University, a co-author on the study.
Once a female mosquito mates she shows little interest in mating again. If she mated with a male that doesn't have viable sperm, the population of mosquitoes would drop.
One method that would not likely work, say the authors, is broadcasting the sounds of mate-ready mosquitoes to deter natural mating. Plus, the buzz of artificial mosquito love songs would likely annoy any humans in the area, since the auditory range of mosquito love songs is well within human hearing range.
All of this research is based on super-glued mosquitoes in the laboratory. Before any sterilized males are tested and released, Gibson points out that more research is needed to confirm that the same principles will work with free-flying mosquitoes.
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