Mosquitoes hate the aroma of common garden catnip, new research shows. And not only are the extracts safe, they are more effective than Diethyl-m-toluamide, or DEET, the chemical used in most commercial insect repellents.
Catnip is one of several plants used in folk medicine to ward off insects, but most people turn to DEET when they want serious deterrence. Now researchers at Iowa State University, Ames, have shown that a relatively weak solution of catnip extract repels mosquitoes as effectively as a DEET solution ten times more concentrated.
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To test the effect, they put groups of 20 mosquitoes in a glass tube which had filter paper in one end treated with either a catnip extract or DEET. Ten minutes later, just over half the insects remained at the end containing DEET-treated paper. In contrast, an average of only 25 per cent remained closer to paper treated with the most potent catnip compound, a monoterpene called nepetalactone.
鈥淓ssential oils of plants have huge potential for insect control鈥�, according to entomologist Joel Coats, who was part of the Iowa team. 鈥淎nd they are very safe for mammalian use.鈥�
The team has previously shown that nepetalactone repels flies and cockroaches. They are applying to patent the compound as a repellant, and hope to register it as a biopesticide with the US Environmental Protection Agency (EPA).
Highly volatile
鈥淲e haven鈥檛 yet tested whether it will work against mosquitoes when on human skin,鈥� says Coats. 鈥淏ut our results are directly relevant to repellency on things like clothing and tents.鈥�
However, the duration of the effect is crucial, according to Jose Ribeiro, a medical entomologist of the US National Institute of 91色情片, Bethesda. 鈥淭o have a smell things have to vaporise, but if they vaporise too fast the effect is lost鈥�, he explains.
DEET is known to have a long-lasting effect and Coats admits that nepetalactone is more volatile than DEET. 鈥淭hat is something that can be worked on in a slow-release formula鈥�, he says.
鈥淎nything that is as good or better than DEET is welcome, because DEET has some side effects鈥�, says Ribeiro. DEET is classified as 鈥渕oderately toxic鈥� by the EPA and can harm birds, fish and aquatic invertebrates. However, the EPA believes it does not present a health concern to the general US population.