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Catnip drives mosquitos away

AMES, Iowa - Although it drives cats wild, catnip appears to be a big turn-off for mosquitoes. In research conducted at Iowa State University, catnip was ten times more effective at repelling mosquitoes than the compound used in most commercial bug repellents. The finding was reported at the 222nd national meeting of the American Chemical Society in Chicago.

Chris Peterson, US Forest Service, and Joel Coats, Iowa State University, studied the effect of nepetalactone on mosquitoes. Nepetalactone is an essential oil in catnip that gives the plant its odor. In past studies, the researchers had found that catnip oils could repel cockroaches.

The researchers placed groups of 20 mosquitoes in a glass tube treated on one side with a high dose of nepetalactone. After 10 minutes, an average of 80 percent of the mosquitoes had moved to the untreated side of the tube. In a low-dose test, an average of 75 percent moved to the untreated side.

The researchers conducted similar tests with DEET (diethyl-meta-toluamide), the compound used in many commercial repellents. In those tests, 55 to 60 percent of the insects moved away from the treated side.

In the laboratory, repellency is measured on a scale from 100 percent (all mosquitoes repelled) to -100 percent (all mosquitoes attracted). In the ISU tests, catnip ratings ranged from 49 to 59 percent at high doses, and 39 to 53 percent at low doses.

Peterson said it took about a tenth as much nepetalactone to have the same repellency as DEET. "In other words, nepetalactone is about 10 times more effective than DEET," he said. "Most commercial insect repellents contain about 5 to 25 percent DEET. Presumably, much less catnip oil would be needed to achieve the same repellency as a DEET-based repellent."

Why catnip repels mosquitoes remains a mystery. "It might simply be an irritant," said Peterson, "or they just don't like the smell."

No animal or human tests are scheduled for nepetalactone, although Peterson is hopeful that will take place in the future. Iowa State has submitted a patent application for the use of catnip compounds as insect repellents. The project was funded by the Iowa Agriculture and Home Economics Experiment Station.

Catnip is a perennial herb in the mint family and grows wild in most parts of the United States. It also is cultivated for commercial use. It's primarily known for its stimulating effect on cats, although some people use the leaves in tea, as a meat tenderizer and as a folk treatment for fevers, colds, cramps and migraines. The plant also is used to make light yellow dye.

For further information, contact Brian Meyer, Agriculture Communications, Iowa State University at (515) 294-0706 or http://www.aginfo.iastate.edu/.