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Better Mosquito, Tick Repellents in the Wind?

By Judy McBride
January 3, 2002

Slap, slap . . . scratch, scratch. It’s a familiar aggravation for billions of people who live with mosquitos. But effective repellents to keep those pests from biting--and possibly transmitting serious diseases--have been few and far between.

Now, the Agricultural Research Service is seeking a patent on a method for selecting the most effective version of a repellent discovered by ARS researchers more than 20 years ago. Using the method, ARS entomologist Jerome Klun recently identified one version that is three to four times more effective at preventing yellow-fever-transmitting mosquitos from biting than the original repellent. It’s also the optimal version against the species that transmits West Nile virus.

The original repellent, called 220 for short, is based on piperidine, a hexagonally- shaped molecule found in trace amounts in black pepper. Two other chemical groups are attached to this hexagon, but each can attach at two different angles. So the repellent can appear in four different versions, known as optical isomers, that can be identified by the way they bend light rays.

The number of potential repellents is not limited to these four optical isomers. Other chemical groups can attach to the piperidine scaffold at various locations and angles, yielding dozens of candidates for testing, according to Klun, at ARS’ Chemicals Affecting Insect Behavior Laboratory in Beltsville, Md.

Interested companies could license the new method to select the most effective piperidine-based isomers against ticks and other disease-transmitting arthropods, as well as mosquitos. Unlike DEET--the principal mosquito repellent for half a century-- piperidine-based repellents don’t dissolve plastics, such as sunglass lenses or auto paint. And early reports from an interested company suggest they easily formulate into creams.

The original piperidine-based repellent has undergone toxicological testing in a U.S. Army laboratory and passed muster for experimental use on people. Also, a related repellent is being sold overseas by the pharmaceutical company Bayer. However, products intended for commercial sale in the United States would have to undergo additional toxicological testing required by the Environmental Protection Agency.

ARS is the chief scientific research agency of the U.S. Department of Agriculture.

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