Scientists have never fully understood how mosquitoes distinguish the smell of human breath and sweat from other odors in nature. To learn more, molecular biologist John Carlson at Yale University and colleagues relied on a mutant strain of fruit fly. Each of a series of mosquito genes that code for smell receptors was transplanted, individually, into the fruit flies, which have an "empty" smell-detecting neuron lacking smell receptors.

Each gene caused the neuron to produce a single kind of mosquito receptor, which binds to odor molecules that have a particular shape. Carlson's team then presented one kind of odor molecule at a time to the flies. If a receptor grabbed that odorant, the neuron sent a signal to the brain indicating the odor's presence, and an electrode implanted next to the neuron revealed the response.

In this way Carlson's lab tested 50 different mosquito smell detectors against 110 odorants. The experiments showed that a small set of smell detectors are highly tuned to sense just a handful of telltale human scents. Identifying chemicals that can fool or block the tuned receptors could lead to improved traps and repellents that can help reduce malaria's spread.

Colleagues of Carlson have taken highly detailed images of the malaria mosquito's smell organs, presented here.

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Note: Images courtesy of R. Jason Pitts and Laurence J. Zwiebel, Vanderbilt University, as published in "Antenna Sensilla of Two Female Anopheline Sibling Species with Different Host Ranges," Malaria Journal, 5:26, March 30, 2006.