In the January 9, 2009, issue of the journal Cell, Vosshall reported further evidence that insects have their own way of smelling. In search of signaling proteins that help relay olfactory messages to the brain, she and postdoctoral fellow Richard Benton mined the genomes of various organisms in search of genes present in fruit flies and mosquitoes but absent in noninsects. They found a new kind of odor-detecting molecule: receptors that are structurally and functionally distinct from odorant receptors.

It was well known that odorant receptors are found on only about 70 percent of a fruit fly's olfactory neurons. The remaining neurons also send signals to the brain in response to specific odors, but how they did it was “a big, dark secret,” Vosshall says.

She and Benton discovered a family of genes that were turned on in olfactory neurons that lacked odorant receptors. The genes' protein products, which they call ionotropic receptors, gave cells the ability to detect specific odors. The researchers had stumbled on a new way that insects detect odors.

Those experiments were done in fruit flies, but the pathway is likely to be common among insects, Vosshall says. It's too soon to say whether targeting that pathway could help them devise a better insect repellent—but it fills in a major gap in knowledge about olfaction and brings Vosshall closer to the complete understanding she is striving for.

Her next step is to find out how identical odors trigger different responses under different conditions. Why, for example, do the cues that signal a human source of blood attract a female mosquito only when she is preparing to lay her eggs? And why does she stop seeking blood once she's had enough?

It's easy to see the practical implications of figuring out how a mosquito's attraction to humans can be switched on and off. In trying to understand the basic biology of olfaction, Vosshall hopes to satisfy her own curiosity about genes and behavior and help conquer some major public health challenges.

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