The Lure of Sex Can Drive Roaches to Their Deaths

In the long and seemingly futile quest to build a better roach trap, researchers have finally identified the come-hither chemical of the female German cockroach and produced a synthetic version that makes males come running in less than nine seconds.

The search for the sex pheromone has been a top priority for cockroach scientists, but it has been an arduous process because the compound is emitted in very small quantities and is so fragile that it easily degrades during laboratory analysis.

The new synthetic version appears to work at least as well as the original, giving scientists hope that they may shift the balance of power in the age-old contest between humans and cockroaches -- creatures widely believed to be capable of surviving nuclear war.

“Chemists have been trying to get this pheromone for decades,” said Wendell Roelofs, a professor of insect biochemistry at Cornell University and one of the study’s authors.

The compound that lures males to their potential mates is so powerful that cockroaches near death from starvation will forgo peanut butter for a chance to copulate, said Coby Schal, a professor of entomology at North Carolina State University and coauthor of the study, published today in the journal Science.

“Invariably, the male will choose the sex pheromone over the food, even though he may die on the way,” Schal said.

German cockroaches -- half-inch long light brown bugs with dark brown stripes -- are the most prevalent roach species in the world.

Widely reviled, they are responsible for spreading food poisoning, dysentery, cholera and other disease and for triggering asthma in children.

U.S. consumers spend more than $1 billion each year to rid their homes of roaches and other pests, according to the Environmental Protection Agency. They barely make a dent in the cockroach population.

Fossil records indicate that cockroaches have inhabited Earth for at least 200 million years.

They are low-maintenance creatures and can survive in a wide range of environments. They can eat almost anything, including linens, cardboard, leather and bookbindings.

Almost any building will become infested after a certain amount of time.

“Whether it’s a restaurant or a warehouse or a farm, cockroaches will somehow find it,” Schal said.

“Once they do, it’s very difficult to get rid of them.”

With a single female roach capable of producing an average of 350,000 offspring in a single breeding season, pest-control experts know they have lifetime employment.

The best they can do to control the pests is to use food as bait to lure them into traps or to catch them on a glue board if they happened to wander onto it.

The pheromone approach promises to be far more effective, said Greg Baumann, technical director for the National Pest Management Assn., a trade group based in Fairfax, Va.

“We would be able to draw them right in, like the runway lights at night at the airport,” he said.

Pest control experts are eager to get their hands on the synthetic pheromone, according to Steve Burt, who runs the professional pest management business in the U.S. for Bayer Environmental Science, maker of the Maxforce line of roach-fighting products.

He said the compound could lure male roaches into a trap baited with poisoned food, some of which they would take back to their colonies. Whole nests could be destroyed as cockroaches ate one another’s feces and even their dead bodies.

“You want the bait to kill them, but you don’t want the bait to kill them too fast,” Burt said. “You want them to go back to their harborages and die there. Then you get a domino effect.”

Researchers have previously isolated pheromones for lesser roach species, but the version for German cockroaches has resisted easy analysis since its existence was confirmed in 1993.

First, scientists at North Carolina State methodically dissected female German cockroaches to find the gland that produces the pheromone.

“It’s like looking for a needle in a haystack,” Schal said.

They then extracted the gland from about 15,000 virgin females and sent them to the New York State Agricultural Experiment Station run by Cornell University.

There, scientists used a gas chromatograph to figure out which chemical in the pheromone compound appealed to male cockroaches.

The gas chromatograph isolated the chemicals one by one. Each was assessed by a disembodied cockroach antenna connected by wire to a detecting device.

When receptors on the antenna recognized the key pheromone ingredient, they fired off electrical signals that the contraption was able to register.

The mystery ingredient was delivered to the State University of New York in Syracuse, where mass spectrometry and nuclear magnetic resonance imaging revealed its chemical structure. A synthetic version of the new compound, named blattelaquinone, was made.

To test their creation, the scientists put male German cockroaches at the base of a 22-inch plexiglass tube with two branches on the other end.

When the synthetic pheromone was introduced into one of the branches, more than 60% of the cockroaches began to track it down.

Of those, nearly all ended up at the pheromone target.

A 100-nanogram dose drew roaches to the sample in an average of 8.9 seconds, the researchers said. When the sample was reduced to 10 nanograms, the roaches still found it in an average of 16.4 seconds.

The researchers aren’t sure why the fake pheromone didn’t affect about 40% of the males. As expected, it had no effect on female or juvenile roaches.

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Sizing up a pest

Size: About half an inch.

Color: Beige to light brown with two dark stripes on back.

Fertility: An average of 350,000 offspring per breeding season.

* One of three main cockroach species.

* Found in virtually every city on Earth.

* No. 1 pest in U.S. homes.

* Gather near food and moisture; infest bathrooms and kitchens.

* Potential carrier of salmonella, dysentery, typhoid, tuberculosis

and polio.

Sources: Science, National Pest Managment Assoc.