perhaps, very selective insecticides? Scientists at Cornell University and els ewhere are trying to
find ans wers to s ome of thes e ques tions , s tudying the defens e mecha nis ms by which many
ins ects protect the ms elves from attack by predators , worki ng out the chemical s tructure of
insect secretions. Other scientists are working on the s o-called ‘juvenile hormone’, a powerf ul
s ubs tance which prevents metamorphos is of the larval ins ect until the proper s tage of growth
has been reached.
Perhaps the mos t i mme diately us eful res ult of this exploration of ins ect s ecretion is the
development of lures , or attractants. Here again, nature has pointed the way. The gyps y moth
is an especially intriguing example. The female moth is too heavy-bodied to fly. She lives on or
near the ground, fluttering about among low vegetation or creeping up tree trunks. The male,
on the contra ry, is a s trong flier and is attracted eve n from cons iderable dis tances by a s cent
released by the female from special glands. Entomologists have taken advantage of this fact for
a good many years, laboriously preparing this s ex attractant from the bodies of the female
moths. It was then us ed in traps s et for the males in cens us operations along the fringe of the
insect’s range. But this was an extremely expensive procedure. Despite the muc h publicized
infes tations in the northeas tern s tates , there were not enough gyps y moths to provide the
material, and handcollected female pupae had to be imported f rom Europe, s ome times at a
cost of half a dollar per tip. It was a tremendous breakthrough, theref ore, whe n, after years of
effort, chemists of the Agriculture Department recently succeeded in isolating the attractant.
Following upon this discovery was the successful preparation of a closely related synthetic
material from a constituent of castor oil; this not only deceives the male moths but is
apparently fully as attractive as the natural substance.
As little as one microgram (1/1,000,000 gram) in a trap is an effective lure. All this is of much
more than academic interes t, for the new and economical ‘gyplure’ might be us ed not me rely in
census operations but in control work. Several of the more attractive possibilities are now being
tes ted. In what might be termed an experiment in psychological warfare, the attractant is
combine d with a granular material and dis tributed by planes. The aim is to confus e the male
moth and alter the normal behavior so that, in the welter of attractive scents, he cannot find
the true scent trail leading to the female. This line of attack is being carried even further in
experiments aimed at deceiving the male into attempting to mate with a spurious female. In
the laboratory, male gypsy moths have attempted copulation with chips of wood, vermiculite,
and other small, inanimate objects, so long as they were suitably impregnated with gyplure.
Whethe r s uch divers ion of the mati ng ins tinct into nonproductive channels would actually s erve
to red uce the population remains to be tes ted, but it is an interes ting poss ibility.
The gyps y moth lure was the firs t ins ect s ex attractant to be s ynthes ized, but probably there
will s oon be others. A number of agricultural insects are being studied for possible attractants
that man could imitate. Encouraging results have been obtained with the Hessian fly and the
tobacco hornworm. Combinations of attractants and pois ons are being tried against several
insect species. Government scientists have developed an attractant called methyl-eugenol,
which males of the oriental fruit fly and the melon fly find irresistible. This has been combined
with a pois on in tes ts in the Bonin Is lands 450 miles south of Japan. Small pieces of fiberboard
were impregnated with the two chemicals and were dis tributed by air ove r the enti re is land
chain to attract and kill the male flies. This program of ‘male annihilation’ was begun in 1960: a
year later the Agriculture Departme nt es timated that more than 99 per cent of the population
backadmin
(backadmin)
#1