Better Bug Spray

As the researchers described in the journal Proceedings Of The National Academy Of Sciences, the collaborative effort looked at the more than 40,000 chemicals examined by USDA, since 1942, as mosquito repellents.

They used molecular modeling software that compared the chemicals’ structure with their function as repellents to predict new chemicals might fend off mosquitoes. Then, they synthesized the compounds and tested them out in a tank of bugs.

Bernier says, "In looking at about 34 different compounds, we found about one third of them that lasted at least as long as DEET and some of them, up to three times as long as DEET." For Bernier, these long-lasting compounds hold particular promise because they one-up DEET. He says, "The exciting news behind the research that we've been working on is the discovery of new repellents that last many times longer than the current gold standard repellent DEET."

But for your next few camping trips, you should still plan on packing DEET repellent. With the new compounds, Bernier says, "It's going to be a lengthy process of making sure they're safe for use on the skin."

Why We Need a Better Bug Spray

In 2007, DEET lovers celebrated the chemical’s fiftieth year of consumer use. Now the most widely used repellent in the United States, DEET has many proponents. The Center for Disease Control and Protection recommends that people traveling to areas with yellow fever and malaria use DEET-containing repellents, and the Environmental Protection Agency says that with proper use, DEET is safe for the general population. Bernier too sings DEET’s praise. "It's been one of our best repellents… On the market today, most of the repellent products that are sold contain DEET," he says.

So by synthesizing new repellent compounds, are scientists reinventing the wheel? DEET has helped prevent countless bug bites, but Bernier says it has a number of drawbacks.

"What we're looking for is some replacements for DEET that might have a little bit friendlier characteristics in terms of people using them. One of the main problems with DEET and the application on certain surfaces, for example plastics—they tend to melt plastics. It tends to also have a sticky feel on the skin, and some people find the odor of DEET offensive," says Bernier. "We're trying to come up with some different chemicals that might solve some of these problems as well as last much longer than DEET does."

Bug repellents aren’t just good for making your picnic pleasant. Bernier says, "on a worldwide scale, mosquito-borne illnesses are probably the number one cause of death and debilitation among humans and other animals." Mosquitoes in the United States also carry diseases such as West Nile Virus, and Bernier says that his team’s research "has a direct impact and potential for use for protecting people from these diseases here in America."

Bernier says the collaboration between chemists and entomologists is key to developing new repellents. "These teams of people got together and we figured out what makes a good repellent, based upon the chemical structure," he explains.

The effort was also a marriage of sophisticated new software and a USDA database built up over decades of testing potential repellents. "We're going back and looking at these chemicals in a new way, using modeling approaches based upon their structure to try to devise and figure out what makes a good repellent," he explains.

"The compounds that we're looking at are similar in structure to DEET," says Bernier, but the chemists made some tweaks.

After using computer models to identify potential repellents, the scientists synthesized the chemicals and then tested them out on muslin strips. A volunteer wearing protective gloves would use his or her arm to lure the mosquitoes. After being dipped into a known concentration of the trial chemical, then allowed to dry, the muslin strip was taped to the volunteer’s arm. The volunteer would hold an arm in a bug-filled cage for one minute, and after researchers had counted the number of bugs attempting to feast, the volunteer was allowed to shake the mosquitoes away.

Each day, the volunteer would suit up again to see if the compound kept repelling mosquitoes, or whether its efficacy flagged. In their paper, Bernier and colleagues describe the results as "astonishing," because, as he explains, "it was not expected that we would have so many good repellents out of this class that would last so much longer than DEET did."

Although some of these compounds may turn out not to be safe for use on human skin, Bernier says "there’s still some opportunity for use, for example, in the clothing repellent market where we might be able to bind these into clothing and use them to protect people."

However, Bernier says "it may be many years" before we know how safe it is to apply these new repellents directly to skin.

This research was published in the Proceedings Of The National Academy Of Sciences and received funding from the U.S. Department of Defense’s Deployed War-Fighter Protection Research Program.