What cats love, roaches loathe; Catnip: Working from tips by interns, scientists find that the active ingredient in the herb is a powerful bug repellent.

The stuff in catnip that intoxicates tabbies repels cockroaches 100 times better than a powerful insect repellent, scientists said yesterday.

The discovery could lead to new nontoxic methods for curbing these tenacious insects, which are more than just a nuisance.


Roach infestations have been linked to rising rates of asthma among children in Baltimore and other inner cities.

"We've been chasing cockroach treatments for three years," says Dr. Peyton Eggleston, professor of pediatrics at Johns Hopkins Children's Center. "If you could do it with a repellent, that would be great."


Chris Peterson and Joel Coats of Iowa State University told a meeting of the American Chemical Society in New Orleans yesterday that they had isolated a chemical that even the loathsome roach finds repulsive.

Now the scientists hope that a chemical manufacturer will use their findings.

"There are plenty of things that kill cockroaches," Peterson said in a telephone interview. "But currently there are no cockroach repellents on the market."

Peterson and Coats began studying catnip a few years ago, when a summer intern told them the plant was resistant to insects.

"We decided to look at the chemical basis of that resistance," he said.

So they boiled catnip leaves and distilled the active ingredient, a chemical called nepetalactone. Then they teased the most abundant form of nepetalactone from another, more elusive form with a slightly different atomic structure.

"The chemistry of catnip has been known for a while, but we're the first to separate the different forms of the same chemical," Peterson said.

They discovered that this rare, more potent form of nepetalactone killed flies. But the work might have ended there if another intern, Leah Nemetz, hadn't told Peterson and Coats that some people put catnip in planter boxes to keep insects away.


She decided to study it as a repellent.

Nemetz soaked half of a piece of filter paper in the chemical and left the other side dry. Then she put the paper and some German cockroaches -- a common species of the insect -- in a dish and watched them scuttle away from the treated side.

Scientists tested their discovery against a widely used repellent, called DEET. Their catnip-derived chemical worked at doses only 1 percent as high.

Iowa researchers have not tested the effectiveness of simply spreading natural catnip leaves around the house. It might require so much of the stuff as to be impractical, Peterson said. And, of course, it might attract a lot of cats.

The two scientists, both entomologists, have also tested the osage orange or "hedge apple," an inedible fruit common in the Midwest, long believed to repel any number of pests. They have not yet isolated the active ingredients.

Of course, when it comes to roaches, most people would prefer to wipe them out.


"The current products available to bait and kill cockroach populations work extremely well, and they work even in situations where you don't have ideal sanitary conditions," said Nancy L. Breisch, an entomologist with the University of Maryland.

But Eggleston, who is engaged in a study of the relationship between roach infestations and asthma, thinks a repellent could fill an important role.

Even after the exterminators leave, residents of infested apartment buildings must be constantly vigilant. They should get rid of houseplants, which attract the bugs.

They have to seal cracks in the walls and be sure to take the garbage out every evening. Food not kept in the refrigerator has to be sealed in containers.

"Insecticides work, but beyond that you have to change your lifestyle," Eggleston says. "It's not easy for people to do that. If we could say, here's some stuff, spray it around each night and it will keep the cockroaches out, that would be easier."

Allergy to roach excrement is thought to be a major cause of asthma in children. Asthma is the most commonly diagnosed pediatric illness in Maryland, and the No. 1 reason why children miss school.


The problem is worse in poor neighborhoods, where roaches thrive. Between 8 percent and 17 percent of school-age children in Baltimore suffer from the disease -- the latter figure more than double the national average.

Nationwide, asthma rates rose 75 percent in all groups, and by 160 percent among infants to 4-year-olds, between 1980 and 1994.

The rate of illness among African-American children is estimated to be 40 percent to 50 percent higher than among whites. Black children are hospitalized with the disease three to five times more frequently than whites, and their death rates are three times higher.