Sweet smell of success

A Yale lab team found that its research subjects were annoying pests. So instead of asking mosquitoes to share the secrets for tracking human prey, the scientists coaxed some potentially lifesaving answers from a more docile insect: the fruit fly.

Not just any fruit flies. These were genetically engineered to incorporate odor receptors from a type of mosquito that transmits malaria—a disease that kills more than a million people a year and infects hundreds of millions more. The scientists tested 50 receptors against 110 odor compounds—one at a time—to see which ones caused the insects’ olfactory neurons to fire most rapidly.

After examining all of the insects’ scent receptors, the team found 24 receptors that responded strongly to compounds in human sweat. The discovery, published in Nature, could eventually lead to mosquito repellents and traps to stem the spread of malaria and save millions of lives.

“We know that mosquitoes find humans through olfaction, but we really don’t know much about how they do it,” says John Carlson, the Eugene Higgins Professor of Molecular, Cellular, and Developmental Biology, who has been working on the problem for nearly a decade. (For more on his malaria work, see “Serial Killer,” March/April 2006.)

The study’s lead author was Allison Carey ’10MD/PhD. Her job was to immobilize a fruit fly, “force it into a little tube so that just its antennae are sticking out, put it under a microscope, and put electrodes in its antennae,” she explains. “Then we can puff in a half-second pulse of odorant, and record the electrical activity before, during, and after.” Carey recorded 27,000 such measurements—what Carlson calls “a heroic amount of work.”

While it will be “several years” before his lab’s work could lead to usable products, Carlson hopes a smart repellent-based approach will have two advantages over traditional insecticides: “it should be much more environmentally friendly,” and “it’s hard for a mosquito to develop resistance to a whole mixture of compounds.”