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The scent of a woman female cockroach

BIOCHEMISTRY: Irresistible Lure for Cockroaches Determined -- Pennisi 307 (5712): 1029b -- Science

Just like many other animals, cockroaches also make their own pheromones. After years of research, chemical formula of the male-luring scent emitted by female cockroaches is discovered. This was a result of painstaking research. The chemical broke down when it was being isolated. Each female cockroach makes so little of it that they had to dissect 15,000 (yes, fifteen thousand) cockroaches to extract enough material to study.

The researchers have been successful in making this chemical synthetically and it has shown to attract male cockroaches. This will be used in the next generation of cockroach control methods.

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In search of mates, frogs croak, birds sing, and cockroaches wear their own special perfume. For almost 10 years, researchers have tried to decipher the chemical formula of the male-luring scent emitted by female German cockroaches. Now that formula is finally in hand. As a result, city dwellers may one day be less squeamish about turning on the light at night: The chemical may result in a "very powerful system" for pest control, says Walter Leal, a chemical ecologist at the University of California, Davis.

On page 1104, Satoshi Nojima, a chemist now at the Shin-Etsu Chemical Co. in Tokyo, Japan, and his colleagues describe the arduous path they took to characterize this chemical, one of several pheromones produced by cockroaches. They also show that a synthetic version of it is a potent attractant for the insects. "It was very difficult to do, very time-consuming," says Robert Kopanic Jr., an entomologist at S. C. Johnson and Son Inc. in Racine, Wisconsin.

German cockroaches are the bane of urban residents. As many as 100,000 can live in a single apartment or house; baits and sticky traps are only moderately effective, and insecticides are not environmental friendly.

So it was exciting news when Coby Schal, an urban entomologist at North Carolina State University in Raleigh, and Dangsheng Laing, now at Atex Bait Co. in Santa Clara, California, reported in 1993 that female cockroaches gave off a volatile compound, or pheromone, that attracts males from meters away. But taking the next step, identifying the pheromone, proved almost impossible. "Every time [we] tried to isolate it, it fell apart," recalls Wendell Roelofs, a biochemist at the New York State Agricultural Experiment Station in Geneva.

Figure 1 Love is blind. A synthetic version of the female scent that attracts males (on female's back) may help with cockroach control.

CREDIT: NOJIMA ET AL., SCIENCE

Adding to the challenge, females produce so little pheromone that researchers needed to dissect 15,000 of them, removing the pheromone-producing gland from each, to extract enough material for analysis. And Nojima--who was working with Roelofs at the time--had to come up with new ways to pin down the attractant among the many compounds in the extracts.

Nojima joined a single detached cockroach antenna to electrodes and exposed it to the chemicals exiting a gas chromatograph, which had separated the roach extract into discrete components. If the antenna sent a signal to the electrodes, he knew he had a good candidate pheromone. The night before he flew back to Japan--his postdoc was ending--Nojima struck cockroach gold when his system recorded a hit. "After 10 years of work, it came down to one night," says Schal.

Fran Webster of Syracuse University in New York found that the newly isolated compound, called blattellaquinone after the cockroach's Latin name Blattella, has a novel structure. But it is similar enough to a commercial product that it is relatively inexpensive to synthesize. The compound clearly attracts male roaches: They prefer the dissolved synthetic pheromone over a control solvent about 93% of the time, on par with their preferences for the natural pheromone. Moreover, field tests at a cockroach-infested pig farm indicate that many males can't resist the synthetic version.

If the compound proves to be effective over long periods, it could be quite useful for pest control, says Kopanic. Even though blattellaquinone only attracts males, they are the wanderers among the two sexes. The new pheromone should lure males into traps or to poison laced with the compound. In the latter case, they would then transfer the poison, through their feces, to females and their young, suggests Schal. If so, for male roaches, the female scent may one day lead to poison, not procreation.