Mosquito War: New Chemicals May Beat DEET

A new study in the Proceedings of the National Academy of Sciences has found several chemicals that may be more effective mosquito repellents than DEET.

DEET has been the gold standard for discouraging mosquitoes for more than five decades — even though until a couple of months ago, scientists didn't know how DEET affects the insects.

The study looks at another approach to find something more potent, but with less worrisome side effects, than DEET. The compound is notorious for having a strong odor, an oily feel — and an ability to melt plastic.

A recent call to Ulrich R. Bernier, found that the U. S. Department of Agriculture chemist couldn't talk — he was too busy being bitten by mosquitoes.

"I probably had on the order of 300 to 400 on my left arm," Bernier later said.

Bernier, who works in Florida, routinely sticks his arm in the box, tightly covered except for one small window of inviting flesh. That little window is protected by a thin cloth that the mosquitoes can bite right through. In tests, the cloth gets coated with candidate repellents.

"If the mosquitoes fly away, then we know it's repellant," Bernier said. "They land on the cloth and walk around, we know we're at the threshold level of repellency."

And when the insects start biting, the repellent is failing.

Bernier recently used the test to look at some interesting new chemicals sent over by researchers at the University of Florida. The scientists had systematically searched through a long list of possible repellents tested over the past 50 years.

It turned out that some of the best belonged to one class of chemicals. By carefully analyzing this class of chemicals, they came up with clues that let them synthesize new repellents that they thought would work.

"I was surprised to see just how good these things were," Bernier said. In his tests, some of the compounds repelled insect attack for far longer than DEET. If you put DEET on a cloth, it works for only around 17 days. Some of the new compounds lasted over three times as long, up to 73 days.

"After trying so many different repellents that people have submitted over the years, it was nice to see some that actually were better than DEET," Bernier said.

The scientist says he likes something else, too — in the past, most repellents were discovered just by testing random chemicals. Not by designing them.

"The biggest implication from this particular study is that we were able to actually predict repellency based on models, synthesize compounds, test them in the laboratory, and get good agreement," Bernier said.

Leslie Vosshall, a scientist at The Rockefeller University in New York, is also on a mission to beat DEET.

"Any efforts to use any approach to improve on DEET should be commended," Vosshall said.

She just recently discovered how DEET works its magic on bugs — something that's long been a mystery. She found that DEET blocks the action of odor receptors.

"Which means," Vosshall said, "that when you're spraying DEET on your skin or your clothes you're creating a microenvironment" that is effectively "blind" to odors.

And if mosquitoes are blind to your odor, then to them, it's as if you were invisible.

Vosshall is now trying to find other chemicals that block the odor receptors. Because her lab's working with cells and proteins rather than mosquitoes and people, she can quickly and cheaply screen massive numbers of chemicals, even hundreds of thousands.

"And we're finding lots of interesting things that look nothing like DEET that are much more potent, at least in the lab," Vosshall said.

But the big question is how they'll work if they're smeared on people's skin. There's a lot more testing to do before any of these candidates could show up on your local stores' shelves.

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