Beyond DEET

Researchers have identified several new substances that appear to ward off mosquitoes for at least three times as long as DEET, a substance widely used in insect repellents, according to a study published recently in the Proceedings of the National Academy of Sciences, the New York Times reports.

DEET has been used for 50 years and is the "gold standard" in mosquito repellents, but new products are needed because of the increasing incidence of malaria and other diseases transmitted by the insects, according to the Times. For the study, scientists from the University of Florida and the US

Department of Agriculture examined the efficacy of acylpiperidines, which are related to the active ingredient in pepper (McNeil, New York Times, 5/27).

Alan Katritzky, the study's lead researcher from the University of Florida, and colleagues rated chemicals on their ability to repel insects based on USDA data of hundreds of chemicals collected over 50 years. The researchers identified the most effective substances and found that they shared the N-acylpiperidines chemical. The researchers then narrowed the study down to 34 molecules - 23 of which had never been tested before, and 11 of which had undergone testing. From those, the researchers narrowed the 10 most effective chemicals down to seven based on toxicity levels and concerns about high costs (Schmid, AP/Google.com, 5/26).

The researchers found that some acylpiperidines could repel mosquitoes for up to 73 days, while DEET typically lasts for about 17 days. The tests were conducted on cloth treated with the chemicals and placed on volunteers' arms. The volunteers placed their arms into cages of mosquitoes for one minute, which is not representative of typical exposure (New York Times, 5/27).

Ulrich Bernier, a research chemist at USDA's mosquito and fly research unit, said he was "surprised" by the results (AP/Google.com, 5/26). He added that it is "neat to see a situation, and this is unique, that things beat out DEET as a repellent. That's just not normal." The findings could help to develop longer-lasting protection against mosquitoes and other insects, especially in developing countries, according to the study authors (Hall, Toronto Star, 5/27).

Additional tests are required to further investigate whether acylpiperidines irritate skin, evaporate, dissolve in sweat or have other negative effects (New York Times, 5/27). Researchers are planning to begin tests on seven of the compounds this summer to ensure that they are safe to use on skin, Bernier said. The study was funded by the Department of Defence (AP/Google.com, 5/26)