WASHINGTON – Scientists have identified the "come hither" scent that female German cockroaches (search) use to lure males, a discovery that may help control one of the world's most troublesome and resistant household pests.
Female cockroaches emit a pheromone (search), or chemical attractant, to let males know they are ready to mate. Researchers earlier identified the courtship chemicals used by other cockroach species, but the romance scent of the German cockroach remained elusive.
"The German cockroach is the one we wanted because it is a worldwide pest that gives all the other cockroaches a bad name," said Wendell L. Roelofs (search), a Cornell University entomologist and senior author of a study appearing this week in the journal Science.
Roelofs said scientists for years could not even identify the gland the female German cockroach used to store and secrete the pheromone. And when the bug did send her mating signal, the chemical was in such a small quantity that it could not be detected and isolated by researchers.
In 1993, Coby Schal of North Carolina State University, Raleigh, a co-author of the study, identified the bug's pheromone gland and sent cells to the Cornell lab. But Roelofs said his team found that the chemical compound in the gland was too heat-sensitive to analyze using gas chromatography, a technique in which the specimen is heated and the compounds are collected and sequenced as they evaporate.
Roelofs said a graduate student in his lab, Satoshi Nojima, developed a low-temperature technique that allowed the chemicals in the mating lure to separate into compounds and then let the male bug show them which compound was the actual fragrance of insect love.
The researchers removed an antenna from a male German cockroach and attached two electrodes to it. The antenna was then exposed to the flow coming from the low-temperature chromatograph loaded with pheromone.
"The male antenna is the only detector in the world that could tell us which compound is active for that species," said Roelofs.
Roelofs said the antenna, which remains alive for hours after removal from the insect, reacted only to a specific chemical compound in the pheromone, thus allowing the researchers to isolate and identify the attractant.
"When a compound elicited a big response from the antenna, then we knew we had it," he said.
The researchers named the pheromone "blatellaquinone." While not very romantic, the name incorporates the formal name of the German cockroach — Blatella germanica.
Roelofs said the pheromone has now been synthesized and tested on male cockroaches. The male bugs love it, he said.
The discovery may lead to a new weapon to control the German cockroach, an insect that is a resistant and tenacious pest in virtually every city on Earth.
Roelofs said the pheromone could be used to attract males to sticky traps or to poisoned baits that the insect would then carry back to other cockroaches. He said Cornell has patented the chemical and would receive money if the pheromone is used by pest control companies.
Michael K. Rust, a cockroach expert at the University of California, Riverside, said the research by Roelofs and his co-authors was "an excellent study" but he is uncertain that a male-attractant would control cockroaches.
"Most of the cockroaches you see running around, about 80 percent, are nymphs (sexually immature cockroaches) that wouldn't be affected by the pheromone," said Rust. As a result, he said, an attractant that improved the efficiency of traps would not have an immediate effect on a typical infestation.
"It might be effective eventually by controlling the males, but I don't think that has been demonstrated yet," said Rust.
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