E. A. Goeldi (1905) Os Mosquitos no Pará.
Memorias do Museu Goeldi. Pará, Brazil.
Ithaca, NY—Flying around on a miniature leash made from a single strand of her human handler’s hair, a female Aedes aegypti mosquito gravitates toward the love song of a prospective mate. As she flies she calls to him by modulating the whine of her fluttering wings. But “he” is merely an iPod earbud playing mosquito tunes. By means of this strange, sterile courtship, Cornell University scientists hope to breed control of mosquito-borne disease.
“For a long time, people just studied how to kill the mosquitoes and not really anything about their mating behavior,” laments Cornell’s Lauren Cator, whose long, blond tresses supply the tethers for her team’s experiments. “But now more and more people are interested in learning about basic mosquito biology because, frankly, extermination is not working out so well in terms of disease control.” Cator and her colleagues are particularly interested in the painful and often fatal viruses carried by A. aegypti: yellow fever and dengue, also known as breakbone fever. Although vaccines have helped to block the spread of yellow fever, dengue has neither prevention nor cure and affects up to 100 million individuals every year in tropical regions around the world.
A. aegypti probably attract the opposite sex using several combined wiles, including the visual appeal they present to each other’s flylike compound eyes and the lure of various chemical signals they emit. But the astonishing acuity of their hearing, which has only just come to light in the Cornell studies, may play the most important role in their mate selection.
The flying female makes a noise, called a flight tone, well known to humans as the whining prelude to a mosquito bite. The sound comes from the beating of her wings and the sympathetic vibration of her thorax, buzzing at a frequency of 400 hertz (close to middle C). The male, being smaller, hums in flight at the higher frequency of 600 hertz. But in the close proximity of courtship on the wing, male and female respond to one another’s sound effects, raising their rates until they synchronize at 1,200 hertz. Researchers call it a “love song,” for when the couple converge on this shared harmonic frequency—far above what mosquitoes were thought capable of perceiving—the two of them copulate.
“There’s really a duet going on here between the male and female mosquitoes,” says Cornell neuroethologist Ron Hoy, widely known as the go-to person for any questions concerning bug ears. “The female is being choosy. And why not? She can up the ante—even check into the male’s physiological fitness by challenging him in this operatic duetting.” Hoy thinks that the speed of the male’s response may reveal his suitability as a father: “Not just ‘How high can he go?’ but also ‘How fast?’ It’s as though they’re singing that song from Annie Get Your Gun, ‘Anything you can do, I can do better.’”
To assess the importance of the love duet, Cator is saving hundreds of mosquito eggs (picture sprinkles of spilled pepper on pieces of paper) from various pairings in the lab. As the eggs hatch, she will try to determine the effect of their parents’ synchronized singing—whether truly harmonious matings produce unexpected benefits, such as offspring that have a longer life span or that lay an increased number of eggs.
Cator’s Cornell colony of A. aegypti live dormitory style, 100 or so together in several metal mesh enclosures, each about the size of an ordinary fish tank, inside a large incubator that maintains a tropical clime. On one side of every cage, the mesh has been exchanged for an expanse of knit fabric—what looks like half a white sweatshirt with one dangling long sleeve, loosely knotted to prevent insect escape. It is through this sleeve that the mosquitoes are fed.
“I don’t feel a thing,” says entomologist Laura Harrington, the senior member of the Cornell team, fitting her own practiced arm through a sleeve and watching a few dozen female A. aegypti alight to feast on her. (Only the females take blood meals, which they require for maturing their eggs; the males survive on flower nectar in the wild and sugar water in the lab.) Harrington could probably delegate this duty to Cator or to some other graduate student in her department, but she considers nurturing these disease-free research subjects part of her job.
