Calling all (brownbanded) cockroaches.

For every cockroach that scurries across the kitchen floor late at night, countless more may hang out behind walls. To determine just how many lurk unseen - or in some cases, to know whether cockroaches are there at all - entomologists are hoping to harness one of these insects' own chemicals.

The chemical is a sex pheromone, a volatile substance used by females to attract males. Placed in a trap, this chemical lures in any nearby males. "There's nothing more sensitive than a pheromone trap," says Coby Schal, an entomologist at Rutgers University in New Brunswick, N.J.

Several kinds of cockroaches use these chemicals, but until now, scientists had only identified and made the one belonging to the American cockroach.

Schal and his colleagues have now isolated and synthesized the sex pheromone of the brownbanded cockroach, a widespread pest that tends to show up in hospitals, research laboratories, and other places where pesticides are not heavily used.

To track down this pheromone, Schal and his Rutgers lab group began about seven years ago to test the response of males to various female body parts. They pinpointed the richest source of this compound: the small porous plates covering two of the segments at the tip of the abdomen, says Schal. The researchers removed these plates from 10,000 cockroaches.

Then, at the New York State Agricultural Experiment Station in Geneva, Wendell Roelofs and Ralph Charlton of Cornell University purified the component of the extracted plates that lures the male. After analyzing the structure and makeup of this compound, Francis Webster and Aijun Zhang from the State University of New York at Syracuse finally synthesized the pheromone.

Even with just 300 molecules on a small filter paper, this synthetic pheromone can attract male brownbanded cockroaches into sticky traps, says Schal, who has begun isolating and identifying the German cockroach's pheromone. The researchers have filed for a patent on the brownbanded pheromone.