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MELISSA BLOCK, HOST:

From NPR News, this is ALL THINGS CONSIDERED. I'm Melissa Block.

AUDIE CORNISH, HOST:

And I'm Audie Cornish. Now for an update on the epic struggle between man and mosquito. The most effective way to avoid mosquito bites, short of staying inside, is by using a repellant called DEET. But no one really understood how the pesky insects detected DEET until now. NPR's Jon Hamilton reports.

JON HAMILTON, BYLINE: The discovery comes from a team lead by Anandasankar Ray at the University of California Riverside. Ray grew up in India and says he knows a lot about the damage caused by blood-sucking insects, especially mosquitoes.

ANANDASANKAR RAY: I have suffered from malaria in my youth. My wife was in hospital with dengue for nearly a week. And so, I have a personal score to settle with them.

HAMILTON: Ray says DEET does keep mosquitoes at bay, but it's too expensive for many people in the countries where mosquito-borne diseases are most common. Also, it isn't recommended for newborns and people have to be careful how they use it. And it can dissolve plastics, including nylon. Even so, Ray says DEET has been the gold standard bug repellent since the U.S. Army developed it in the 1940s, despite many efforts to find something better.

RAY: The main reason why scientists haven't been able to improve upon DEET is because they just didn't know how DEET is detected by the insects.

HAMILTON: Ray decided to find out using genetically modified fruit flies. These custom-made flies have special nerve cells in their antennae that glow a fluorescent green when they react to DEET. Researchers in Ray's lab exposed the flies to the repellent. Then, Ray says, a scientist named Picky Kain examined the flies' antennae under a microscope.

RAY: When Pinky found the neurons that were fluorescing green, she came running into the lab in joy, saying that finally we think we have a candidate class of neuron that is being activated by DEET.

HAMILTON: Ray says more tests showed that they really had found the specific part of a nerve cell that detects DEET and tells a bug to find a meal somewhere else.

RAY: However, we were faced with a second challenge, which is how can we leverage this finding and use it for the good of humanity?

HAMILTON: Another researcher in the lab had an answer. He used the new information about DEET detection to screen a half million chemical compounds. Of those, a couple hundred appeared likely to repel insects. And from this group, Ray and his team picked three that are already approved by the FDA as food additives.

RAY: One of them is present in plum. The other is present in orange and jasmine oil. Some of them are present in grapes. And as you can imagine, they smell really nice.

HAMILTON: Ray says the compounds are cheap, safe enough to eat and don't dissolve plastic the way DEET does. But do they keep away mosquitoes? To find out, researchers put on a special glove and placed their arms in a cage filled with hungry insects. Ray says the glove has a window in it that is covered with netting.

RAY: When we offer our arm, mosquitoes are really excited. They sit on the netting and try their level best to probe. However, when we treat the net with one of these repellent compounds, the mosquitoes are no longer attracted.

HAMILTON: And that's pretty big news in the insect world. Craig Montell at the University of California Santa Barbara also has studied how bugs react to DEET. He says he's impressed by the new research and thinks the world could use some new repellants.

CRAIG MONTELL: Although DEET is not highly toxic, it's not completely safe either and the particular repellants that they found seem like they're safer than DEET.

HAMILTON: Montell says the finding could make a dramatic difference in developing countries where millions of people suffer from malaria and dengue. But he thinks people in the U.S. would benefit, too.

MONTELL: We certainly would love to have better, more effective insect repellents than DEET so that we can have a pleasant picnic on a pleasant summer afternoon in our backyards without getting eaten alive by mosquitoes.

HAMILTON: The new research appears in the journal Nature. Jon Hamilton, NPR News.

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