It’s the time of year when many parents are wondering which is worse: mosquitoes, or mosquito repellents. Since mosquitoes can cause dangerous diseases like West Nile virus, experts recommend wearing bug repellents when spending time outdoors—even though the most effective repellents are also toxic to people.

But as this ScienCentral News video reports, scientists searching for safer repellents are finding a lot of promise in something most of us consider a cat’s toy.

A natural repellent?

Joel Coats and his colleagues in Iowa State University’s Department of Entomology report that the oil distilled from the common catnip plant effectively repels mosquitoes in laboratory experiments. The group has presented its research at the 2002 annual meeting of the North Central Branch of the Entomological Society of America.

The scientists have been investigating the insect-repellent properties of catnip and other folkloric herbs for years, but catnip is the first essential oil they’ve tested on a species of mosquitoes.

"The mosquitoes we tested were Aedes aegypti, known as the yellow fever mosquito," says Coats. "It occurs somewhat in the Southern United States and lots of Latin America, and has been the cause of dengue fever as well as yellow fever there. We think it responds in a fairly typical way and other mosquitoes would be repelled as well."

Coats says the point of the research is to seek natural alternatives to chemical sprays. "I think our most important contribution probably is to show there are natural alternatives and that the synthetic compounds like DEET aren’t the only way we can repel mosquitoes," he says.

What is DEET?

DEET is the name for the chemical, invented in 1946, that is generally considered the most effective active ingredient in commercial mosquito repellents. Although its safety record led the US Environmental Protection Agency’s Office of Pesticide Programs to re-approve its use in 1998, serious concerns about its safety are behind the growing popularity of botanical alternatives.

The problem with currently available alternatives, such as products containing citronella oil or the active ingredient in eucalyptus is, they just aren’t as effective as DEET. That’s what makes Coats’ evidence that catnip oil and its active ingredient nepetelactone are even more effective than DEET so exciting.

How does it work?

They’re working on that question. Coats says how insect repellents work isn’t well-understood, nor is how catnip works on cats!

According to the Purdue University School of Veterinary Medicine’s Index of Plants Poisonous to Livestock and Pets, catnip’s intoxicating effect on cats qualifies as low toxicity.

But Coats thinks nepetelactone’s insect repellency is somehow olfactory. The group’s earlier work with cockroaches contributes a clue: when they gave some cockroaches "antennectomies," which is to say, they snipped off their antennae, the roaches no longer responded to catnip oil. "We found that the ones with antennae were quite repelled while the ones that had been antennectomized did not sense the repellent and they were responding behaviorally in a very random way," says Coats.

Catnip is not considered toxic to humans and catnip oils are widely sold as herbal medicinals. But Coats says before it could be used as an active ingredient in commercial mosquito repellents, it would have to be tested on animals and people. "Most of the repellents like citronella or DEET are in a solution that’s not 100-percent oil," he says. "So I wouldn’t try it on yourself personally." Iowa State University reports its Research Foundation has filed patent applications based on Coat’s repellent research.