Will the real Asian roach please stand up?

Will the real Asian roach please stand up?

Possibly the only redeeming value ofroaches is that they scatter when the light's turned on.

Ah, but wait. Enter the Asian cockroach,Blattella asahinai. Unlike its cousins it's liable to just stand there and get in the way of the mustard jar when you get up for a midnight snack. And if that's not bad enough, it's likely to take wing and follow you to the next place you flick on the light switch.

To the novice, the Asian roach--firstfound in Florida just three years ago--is easily mistaken for North America's most prevalent household variety, the German cockroach. In fact, even the experts have a hard time telling the difference. But researchers at the U.S. Department of Agriculture in Gainesville, Fla., have recently developed a detection technique using a chemical assay that distinguishes the Asian roach from the German variety 100 percent of the time, says organic chemist David A. Carlson. The technique will allow other researchers to monitor the spread of the Asian cockroach, says Carlson, who developed it with Richard J. Brenner. Carlson will present his findings later this year at the annual meeting of the Entomological Society of America in Boston.

Carlson's technique is an adaptation ofone he developed to differentiate Africanized bees from their European cousins (SN: 4/4/87, p.218). To identify the Asian roach, researchers experimented with roaches using an assay for cuticular hydrocarbons, the chemicals found in the outer waxy layer that covers the roach's whole body. The technique involves washing the roach, or any part of it, in hexane to remove the wax. The solution is then injected into a gas chromatograph, which measures the quantity of different hydrocarbons. Readings from the chromatograph show distinct peaks corresponding to the different molecular weights of chemicals in the wax of each species.

Currently, U.S. scientists have only confirmedthe Asian roach in Florida, where it has taken up residence in 800 square miles near the Tampa area and can occur in concentrations of 100,000 per acre, says entomologist Philip G. Koehler of the University of Florida in Gainesville. Mostly an outdoor roach, it will infest an entire yard, showing frenzied activity each day shortly after sunset, crawling to the top of grasses and leaves and possibly getting into the house. It then begins calming down and mates at about 2 a.m., only to become active again just before dawn to return to the leaf mulch. Three weeks after mating, the female develops a capsule filled with about 40 eggs, which develop into adults some seven weeks after birth, Koehler says.

Some entomologists believe the roachcould reach into the Gulf states, up the East Coast to Maryland and New Jersey, and up the West Coast as far as Washington state.

Photo: The female and male German cockroaches,left, show a striking resemblance to their Asian counterparts, right.