Science: Synthetic Siren Song

The gypsy moth, a European immigrant that defoliates forests in New England and is threatening the Middle West from a beachhead near Detroit, may soon be undone by synthetic sex. Martin Jacobson, Morton Beroza and William A. Jones, all of the U.S. Agricultural Research Service, tell in Science how they have isolated and synthesized the powerful chemical lure with which female gypsy moths attract their males.

Entomologists have known since 1913 that an essence extracted from the abdomen tips of female gypsy moths would bring excited males from as far as half a mile away. For years they used this natural extract as bait in traps set out to locate colonies of the destructive moths, but the stuff was much too scarce for more than small-scale use.

In 1957 Dr. Jacobson started the delicate job of identifying the moths’ chemical siren song. He began with 500,000 female gypsy pupae collected in Spain and Connecticut. When the virgin moths (female gypsy moths lose their siren scent at the same time as their virginity) emerged, the tips of their abdomens were snipped off, dropped into benzene.

The crude extract from this first step was purified and separated into fractions by treatment with various chemicals, and each fraction was tested for sex attractiveness. A slender glass rod was touched to the sample and brought near the antennae of a male moth held in wing clips. If he fluttered and made mating motions, the sample was adjudged to contain the sexual lure of the 500,000 martyred virgins.

At last the chemists isolated a small drop (20 mg.) of colorless, oily stuff, odorless to humans but with an enormous attraction for male gypsy moths. It could be diluted almost endlessly. Less than one ten-thousandth of a billionth of a gram (10 -7 microgram) of it was enough to bring eager males fluttering out of the woods. When the potent oil was analyzed, it proved to be a surprisingly simple chemical (10-acetoxy-1-hydroxy-cis-7-hexadecene) that can be synthesized for $5 per Ib. Dr. Jacobson has about 1 Ib. on hand. If it were diluted and used to bait traps at the present rate, it would last for 300 years, but the Department of Agriculture has bigger ideas. By liberally sprinkling an infested area with synthetic sex lure mixed with poison, it hopes to exterminate the gypsy moth males, dooming the females to chastity. If this tactic works, the next step will be to synthesize the lures of other pestiferous insects.