Sweet Scent Repels Mosquitoes

Mosquito-borne diseases kill more than one million people worldwide each year, with millions more sickened, according to the American Mosquito Control Association.

Now, researchers from the University of California, Riverside have discovered a potential way to reduce the transmission of diseases like malaria, dengue fever, and West Nile virus by turning the mosquitoes’ sense of smell against them.

Dual-Purpose Receptors Help Mosquitoes Find Meals

Female mosquitoes use two methods to track down tasty humans. From a distance, mosquitoes follow the trail of carbon dioxide released from the lungs each time we exhale.

Once mosquitoes are closer to their intended human target, however, the insects begin to pick up the alluring scent of body odor, a signal that the bare skin café is open for business.

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In a new study, published today in the journal Cell, researchers led by Anandasankar Ray, Ph.D., an associate professor of entomology, discovered that one of the olfactory receptors mosquitoes use to detect carbon dioxide is also sensitive to the odor of skin, even when no carbon dioxide is present.

"It was a real surprise when we found that the mosquito's carbon dioxide receptor neuron, designated cpA, is an extremely sensitive detector of several skin odorants as well,” said Ray in a press release, “and is, in fact, far more sensitive to some of these odor molecules as compared to carbon dioxide.”

Tasty Compounds Misdirect Mosquitoes

When the researchers chemically blocked this receptor, mosquitoes were less attracted to human foot odor.

Next, the researchers screened about half a million existing compounds to identify ones that could block or activate this particular receptor.

Based on smell, safety, cost, and whether or not they occur naturally, the research team narrowed the list of compounds down to 138 possibilities. Many of these are already approved and generally recognized as safe.

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The researchers finally settled on two potential substances. The first, ethyl pyruvate, is a fruity compound that is approved as a flavoring agent in food. When applied to a person’s arm, this compound deterred mosquitoes from biting by “masking” body odor.

The other compound, cyclopentanone, had the opposite effect on mosquitoes—luring them in like carbon dioxide. If effective, this minty compound could replace more costly carbon dioxide sources—such as burning fuel or evaporating dry ice—used in current traps to lure mosquitoes in.

Because they are natural, inexpensive, and pleasant-smelling, people may be more likely to use these fruity and minty compounds than traditional mosquito repellants. In addition, they could form a double barrier of protection against mosquitoes.

“These potentially affordable 'mask' and 'pull' strategies could be used in a complementary manner, offering an ideal solution and much needed relief to people in Africa, Asia, and South America—indeed wherever mosquito-borne diseases are endemic,” says Ray. “Further, these compounds could be developed into products that protect not just one individual at a time but larger areas, and need not have to be directly applied on the skin."

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