The Moth's Allure

One of nature's most baffling phenomena has been the extraordinary power of female moths to attract mates over long distances. In one experiment, a female emperor in a gauze cage collected 127 males of her species in seven hours; male Chinese silkworm moths have been known to home in on intended mates from as far away as seven miles. Since a female under a bell jar will stir nothing in males on the outside only inches away, biologists have concluded that the secret of her charm must be an odor--from a substance so strong that a few molecules send males fluttering into the wind, and so selective that only males of her own species are attracted.

In a massive experiment conducted by Adolf Butenandt, 56, who was co-winner of the 1939 Nobel Prize in Chemistry (for isolating the male sex hormone, androsterone), a research team at Munich's Max Planck Institute for Biochemistry imported 1,000,000 silkworm cocoons from Italy and Japan, opened them up with razor blades, separated the pupae of 310,000 females from the males. What followed, in the words of one researcher, was "a mass slaughter, and not for the fainthearted." Each tiny pupa was disemboweled, the scent glands carefully cut out. Male moths served as lab assistants: when they were placed near fractions into which the gland material had been divided, their fluttering wings told the scientists which parts contained the magic substance.

Finally isolated, it turned out to be a yellowish, fatty substance with a subtle, not unpleasant odor of leather. Study of its chemical structure revealed a relatively simple formula: C10H30O-- technically an alcohol. The million cocoons had yielded only a barely visible 1.6 mg.

Most moths are not pests in themselves, but their larvae are--e.g., the larvae of the gypsy moth destroy thousands of trees every year. Butenandt's discovery opens the way to a new attack on such pests. Insecticides kill off useful insects along with the pests. But if the sex attractant for one particular species can be isolated and synthesized, its males can be attracted, trapped, and killed without harming useful insects.

"The males will come flocking," said a Munich researcher. "Females, of course, will continue to lay their eggs, but they will be unfertilized. The main advantage over DDT is that no resistant strains are likely to emerge. Whoever heard of a male animal becoming immune to sex?"

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