Catnip and Osage Orange Components Found to Repel German Cockroaches

Research in the lab of Dr. Joel Coats in the Department of Entomology at Iowa State University indicates that chemicals produced naturally by two plants, catnip and the osage orange (also known as hedgeapple) repel German cockroaches. Folklore includes numerous claims that catnip and osage orange are repellent to insects and spiders. Results presented at the American Chemical Society National Meeting in New Orleans, LA, August 22-26, show that when given a choice between a surface treated with these plant oils and an untreated surface, German cockroaches spent much more time on the untreated surface. Graduate research assistant Chris Peterson observed the responses of the cockroaches. He said that "the roaches will venture onto the treated surface, stop, turn around and walk off onto the untreated surface."

Catnip, well known for its intoxicating effect on cats, contains a chemical called nepetalactone. This compound is present in two isomers, which were isolated and tested individually for their repellency. The researchers reported that the minor isomer (the E,Z-isomer) was 5 to 10 times more repellent than the principal isomer (Z,E).

The essential oil of osage orange is also repellent to the German cockroach. Three of the compounds in the oil have been identified, while several others have not been. Identification of the repellent components is currently underway. Their individual and aggregate repellencies will be investigated on roaches, as well as other insect pests.

Potential applications include use as barrier strips to prevent cockroach entry into an area, or in packaging and shipping where treated containers may prevent accidental transportation of cockroaches with food items. Coats believes that there are sensitive areas in which natural roach repellents may be much preferable to spraying with conventional insecticides; such areas would include schools and daycare centers, hospitals, restaurants, kitchens, and bathrooms. "The essential oils of plants hold great potential for insect control, as natural insecticides and repellents," he says. Tests at Iowa State are currently being conducted to determine the activities of the catnip isomers and osage orange oil components against other insect other insect pests. "We're very interested to see if these compounds are active against mosquitoes, house flies, ticks, chiggers, black flies, pests of stored products, as well as other species of cockroaches," Peterson says.

In the current study, the osage oranges and catnip plants themselves have not been proven to repel insects in houses or other buildings. However, the extraction and confirmation of repellent compounds from these plants will hopefully lead to the development of effective natural repellents. Three years of research by Peterson and several other researchers in the Coats lab has culminated in the Iowa State University Research Foundation filing two patent applications on the repellents developed from the studies.