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Some grape-scented compounds repel mosquitoes

Molecules drive bugs away as well as DEET does

A screen coated with the compound MDA (methyl N,N-dimethyl anthranilate), bottom, keeps female mosquitoes at bay. The chemical smells like grapes and is deemed safe for humans.

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A newly discovered batch of safe bug repellents works just as well as DEET, scientists report October 2 in Nature. As an added bonus, these new bug dopes smell faintly of grapes.

In addition to finding the new bug-repelling compounds, the scientists also uncovered the elusive cells and proteins that let mosquitoes detect and avoid DEET. This knowledge “gives you another whole set of tools” in the search for new insect repellents, says neuroscientist Mark Stopfer of the National Institutes of Health in Bethesda, Md.

DEET has been around for more than 60 years without scientists knowing how insects detect the molecule. “It’s remained a mystery for so long,” says entomologist Anandasankar Ray of the University of California, Riverside. Using a genetic trick, Ray and his colleagues engineered fruit flies — a proxy for mosquitoes — so that neurons would glow when active.

After exposing the flies to DEET, the team identified neurons that responded in a pit in the antenna called the sacculus. These cells harbor a protein called Ir40a, a receptor present in many other insects. When the scientists silenced these Ir40a neurons, the flies grew impervious to DEET.

Knowing which cells make insects abhor DEET allows scientists to test other possible bug repellents by applying them to those neurons, Ray says.

He and his colleagues tested candidates after using a computer algorithm to comb through thousands of compounds, looking for those that had chemical features similar to DEET and other known repellents. To restrict their search to molecules that were likely to be safe to humans, the scientists looked for chemicals that either originate from plants or animals, or are already approved as fragrances, cosmetics or flavors.

Three molecules suggested by the algorithm — chemicals known as anthranilates — activated these Ir40a cells and repelled mosquitoes. What’s more, these compounds, which occur naturally in grapes, plums or orange flowers, are approved for human consumption or oral inhalation by the Food and Drug Administration. Unlike DEET, these compounds don’t dissolve plastics.

With further testing these compounds or others that emerge from the project might be useful in regions that struggle with mosquito-borne illnesses such as malaria, Ray says. DEET is difficult to use, may harm health and is expensive.  “Cost stops it from being used in the areas of the world where it is most needed,” he says.  

Because many insects have the Ir40a receptor, the new repellents might prove noxious to other insects, such as bedbugs, cockroaches, ants and agricultural pests. The team plans to test the compounds on more insects, and Ray may start a company to develop and distribute these new repellents.

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