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For Pesky Mosquitoes, the Latest Buzz Is Bad

Riverside, CA — For thousands of years, civilizations have dreaded the high-pitched whine and irritating welts of mosquitoes — and the deadly infections they carry.

undefinedNow UC Riverside researchers have made the reign of these supreme parasites less secure. They’ve solved the nearly 70-year-old mystery of how the repellent DEET deters mosquitoes and other bugs. Safer, cheaper and more effective repellents are now feasible.

The research team identified the precise areas in the antennas of mosquitoes that detect DEET, structures that have long eluded discovery. Using some clever reverse-engineering, they then identified three chemicals that also repel mosquitoes, but don’t dissolve plastics or pose toxicity risks, like DEET can.

Moreover, the chemicals are already approved for other uses, and so can be more quickly incorporated into repellents against mosquitoes and other bugs. They’re also cheaper than DEET, said Anandasankar “Anand” Ray, an associate professor of entomology, who led the research.

The all-UC Riverside study was published Wednesday in the scientific journal Nature.

There’s no way of knowing when the improved repellents will hit the market, Ray said. But now that they’re known to exist, he said the federal government, private industry and charitable organizations should make them a priority.

The study builds on earlier research by Ray and colleagues about blocking mosquitoes from sensing their prey. That study was published in 2011, also in Nature.

There’s a growing need for improved repellents to fight mosquito-borne diseases, said Emmanuel Theodorakis, a UC San Diego professor of chemistry and biochemistry, who has studied chemicals that repel the bloodsuckers and other pests. The research represents “a novel approach to the rational design of insect repellents,” Theodorakis said, referring to the reverse-engineering.

Malaria kills 1.2 million people worldwide each year, mostly in poor countries with inadequate health care systems. Dengue, West Nile virus and yellow fever are also major public health risks in many countries. West Nile virus from mosquitoes is a concern in the United States.

“Insect repellents such as DEET, a compound developed by the U.S. Army in 1946, are slowly becoming less effective as shields against these insects and, given their inherent limitations, they are likely to become obsolete in the near future,” Theodorakis said.

“The approach highlights the use of modern biological and computational techniques that, in synergy with synthetic and medicinal chemistry, provide the foundation for the identification of new and potent insect repellents.”

Ray and colleagues discovered the olfactory receptors that detect the presence of DEET. Called Ir40a receptors, they line the inside of a part of the antenna called the sacculus.

The team then screened 500,000 chemicals with a computer algorithm for predicted activity against the receptors. They found nearly 200 potential DEET substitutes, then tested 10 of the most promising for repellent activity.

Eight of these 10 strongly repelled flies, and four of those tested on Aedes mosquitoes, carriers of yellow fever and dengue fever, also repelled them, Ray said. Of the four, three are food additives already approved by the U.S. Food and Drug Administration. But before these could be sold as repellents, they must be certified by the U.S. Environmental Protection Agency, Ray said. And for widespread use in poor countries, low cost is vital.

Many more chemicals remain to be tested, Ray said, and some of those could repel mosquitoes far more strongly than DEET, he said.

Ray said the new research complements the 2011 Nature study on blocking mosquitoes from detecting prey. That study described how mosquitoes can be prevented from sensing carbon dioxide, which is a powerful lure. Every exhaled breath emits carbon dioxide that mosquitoes can follow upwind to the source.

While blocking that sensing doesn’t actually repel mosquitoes, Ray said it stops them from congregating around people. This greatly reduces the chances of being bitten. A company called Olfactor Laboratories in San Bernardino has brought the technology to market in a wearable patch.

Combining the technologies could create an even stronger repellent, Ray said.

Meanwhile, Ray’s lab continues to study what chemicals draw mosquitoes to their prey. Skin odors play a big role.

“While carbon dioxide is the primary cue that draws mosquitoes very close, it’s well known that dirty socks, for example, or houses where human beings are not present are attractive to mosquitoes,” Ray said. “In the presence of carbon dioxide it becomes super-attractive.”

More effective mosquito lures can be made using these chemicals, he said.

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