One form of the chemical in catnip repels cockroaches 100 times better than DEET, the basis for commercial bug repellents, Iowa State University scientists told a meeting of the American Chemical Society on Monday.
Chris Peterson and Joel Coats said they began studying catnip a few years ago when a summer intern told them it was resistant to insects. The pair boiled catnip leaves and distilled the active ingredient, a chemical called nepetalactone.
Peterson also has found roach-repellant compounds in an inedible softball-sized fruit called the Osage orange or hedgeapple, but doesn't know which specific chemical creates the roaches' "yuck" response.
The Osage orange is sometimes sold in groceries because of folk wisdom that putting the fruit in cupboards or basements will repel just about any bug, they said. The fruits are filled with a sticky substance that turns rubbery when exposed to air, they said.
The discovery could lead to new nontoxic methods for curbing the tenacious insects, which are more than just an annoyance around the house. The rate of asthma among children, particularly in cities, is rising. Scientists say the reason is an allergic reaction to roach excrement.
"We've been chasing cockroach treatments for three years," Dr. Peyton Eggleston, a pediatrics professor at Johns Hopkins University Children's Center, told the Baltimore Sun. "If you could do it with a repellent, that would be great."
The researchers tested repellent power by flooring a cage with treated and untreated filter paper, and measuring how much time the roach spends on each side during a five-minute test.
Although most people would prefer to kill roaches outright, a repellent might be an effective way to keep them out of the house after the exterminators have left.
So far, they have only studied the small brown German cockroaches, rather than their thumb-sized American cousins. They are just beginning to look at mosquitoes.
Roaches have sense organs on their antennae, feet and mouths. The "feelers" seem to be the spot affected by both catnip and osage oranges, the researchers said.
They have not tested the effectiveness of spreading catnip leaves around the house. While it might help turn away a swarm of cockroaches, it could lead to a new infestation -- writhing, blissed-out cats.