Catnip Repels Mosquitoes More Effectively Than DEET

Sometimes scientific discoveries come in the form of all new compounds—perhaps not attainable before technology stepped in. Other times, research into the habits of earlier civilizations leads to equally important findings. Such appears to be the case in the study of plant essential oils for insect repellents. Entomologist and toxicologist Joel Coats was following the folklore that surrounds insects and catnip when he made a very important discovery.

Last September, entomologist Chris Peterson, Ph.D., with Joel Coats, Ph.D., chair of Iowa State University’s Entomology Department, released their research findings that nepetalactone, the essential oil in catnip that gives the plant its characteristic odor, is about ten times more effective at repelling mosquitoes than DEET — the compound used in most commercial insect repellents.

Peterson put groups of 20 mosquitoes in a two-foot glass tube, half of which was treated with a 1.0 percent 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 same tests with DEET (diethyl-m-toluamide) resulted in 55 to 60 percent of the insects moving away from the treated side.

Peterson says nepetalactone is about 10 times more effective than DEET because it takes about one-tenth as much nepetalactone as DEET to have the same effect. Most commercial insect repellents contain about 5 percent to 25 percent DEET. Presumably, much less catnip oil would be needed in a formulation to have the same level of repellency as a DEET-based repellent.

Many people do not realize that DEET is a pesticide, and it is absorbed through the skin. Excessive use of DEET can also pose health risks and young children are at the greatest risk. A Duke University Medical Center pharmacologist warns people to be cautious when using the insecticide DEET after his animal studies found the chemical causes brain cell death and behavioral changes in rats after frequent and prolonged use.

A safe and natural alternative to DEET is certainly desirable and Peterson thinks it would not be too difficult to produce an insect repellent using catnip oil. Extracting nepetalactone oil from catnip is fairly easy, he says. "Any high school science lab would have the equipment to distill this, and on the industrial scale it’s quite easy."

Why catnip repels mosquitoes is still a mystery, says Peterson. "It might simply be acting as an irritant or they don’t like the smell. But nobody really knows why insect repellents work."

A patent application for the use of catnip compounds as insect repellents was submitted by the Iowa State University Research Foundation.

Catnip is a perennial herb belonging to the mint family, is native to Europe and was introduced to this country in the late 18th century. It is primarily known for the stimulating effect it has on cats, although some people use the leaves in tea, as a meat tenderizer and even as a folk treatment for fevers, colds, cramps and migraines.

At Log House Plants, we have experimented with fresh catnip leaves and catnip oil and found them to be very effective and easy to use. Simply rubbing fresh catnip leaves over bare skin allows us venture into the garden even at dusk when the mosquitoes can be vicious.

Sources: Florida Environment Radio, American Chemical Society, CBC News

Copyright Log House Plants 2002