8,000 Dangerous Females

The white-trimmed brick building at Beltsville, Md., is swarming with frustrated maidens and looks like a young ladies' finishing school. But there are no students among the 8,000 carefully segregated females who live there. They all work for the U.S. Department of Agriculture, and they spend their lives in milk cans warmed by a gentle stream of air. Raised and cared for by Entomologist Robert T. Yamamoto, these sex-starved cockroaches are fed on dog meal, and their only job is to exude a sex lure that drives male cockroaches crazy.

Entomologists have long known that female cockroaches use perfume to advertise their nubility. Army chemists at Natick, Mass., once extracted a powerfully attractive substance from filter paper crawled over by virgin females, but it was mixed up with too many other materials to be analyzed successfully. The Beltsville system is better; the air passing through the cans carries the cockroach perfume to a flask cooled by Dry Ice. There the vapor condenses and is periodically collected. After an elaborate purification process, Dr. Yamamoto has saved up 12.2 milligrams (.0004 oz.) of pure attractant, equivalent to the perfume produced by 10,000 virgin females advertising themselves over a nine-month period.

Active Oil. The yellow liquid has only a faintly oily smell to human nostrils, but what it does to male cockroaches is a sight to behold. Only a bit more than one-third of a thousandth of a billionth of a billionth of an ounce wafted into their cage starts them running around madly, vibrating their wings and trying to mate with each other.

After Dr. Yamamoto collected a working amount of sex lure, his colleagues. Chemists Martin Jacobson and Morton Beroza, determined its chemical structure. This called for long and delicate procedures. At last, the chemists decided that the active attractant is 2.2-dimethyl-3-isopropylidene-cyclopropyl propionate. In spite of its formidable name, it is not very complicated for an organic compound, so Jacobson and Beroza are sure that it can be synthesized in quantity without much trouble.

Sneaky Scheme. When this is done, it may mean the end for at least one kind of cockroach, Periplaneta americana, the species bred by Dr. Yamamoto. The males cannot resist its attraction, so they can be lured easily into baited traps. But this simple scheme does not satisfy the anti-cockroach forces. The females will not be affected, they point out, and a few males attracted to them in the age-old way will work overtime to make them lay fertile eggs.

Much better, say the Beltsville entomologists, is the sneakier scheme of using synthetic sex lure to trick the males into crawling over a chemical that will sterilize them but do them no harm in any other way. They will mate normally with normal females whenever they get the opportunity.

Once the females have mated, they lose all their scented appeal. They lay about 14 eggs per week for the rest of their lives while the males take no further notice of them. But each female that has mated with a sterilized male lays only infertile eggs. If most of the males in a given locality have been sterilized, then most of the females will have no living offspring, and the cockroach population will plunge toward zero. The same unsporting trick, say the Beltsville scientists, should work on other insects that use sex perfumes, including bollworms, army worms and corn borers.

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