Just as gypsy moth damage to Northeast woodlands has reached record-breaking heights (5.1 million acres in 1980), a light has appeared at the end of the control tunnel. A "breakthrough" is how the US Department of Agriculture DA has described the development of a timed-release sex attractant that, once applied, will efectively disrupt mating all summer long.
Four years of field testing by the USDA suggests that an application of a little as 12 grams of the pheromone (sex attractant) to the acre reduces mating in moderately infested areas by 90 to 98 percent (94 percent in closely monitored tests in Maryland last year).
Back in 1970 US scientists isolated the sex attractant of the female gypsy moth and reproduced a synthetic duplicate. But the hoped-for breakthrough in moth control did not occur because of a lack of a suitable way to apply the pheromone. It readily biodegraded when exposed to air and rain, so that to be successful it would have to be applied regularly throughout the season at costs too prohibitive to contemplate. Now, however, a sandwich type of material has been developed that protects the pheromone while allowing a steady release of the scent over several months.
The time-release material, applied as a trap (in home gardens), as a tape around tree trunks, or sprayed in minuscule flakes over large areas, confuses the male moth.In effect the forest becomes saturated with the attractant so that the male, which can pick up the female's scent from a quarter of a mile away, receives no clear directions. In this case, only the accidental sighting of the female makes mating possible.
In the Maryland tests, female moths were placed in cardboard shields, freely accessible to the male moth. Where none of the confusing attractant was placed in the area, the males readily flew to the females; when it was present, only "dumb luck," as some researchers expressed it, enabled the male to find the female. The gypsy moth pheromone is harmless to all other insects, birds, or animals.
In heavily infested areas it has been found that the visual sighting of female moths by males reduces the effectiveness of the synthetic pheromone. In this insance the USDA recommends the application of a spray (biological or chemical) in the larval stage, after which the confusion technique can be used when surviving caterpillars emerge as adults in June.
Meanwhile, the extremely cold winter in much of the Northeast may boost the effectiveness of the pheromone treatment by reducing the number of surviving egg clusters. Heavy infestations would then become moderate infestations, thereby reducing the number of accidental sightings during the mating season.
Absurd as it now sees, it was an attempt to develop a hardy strain of silkworm that brought the gypsy moth to New England. One day in 1869 a package of eggs of a particularly winter-hardy French moth arrived at the home of a naturalist, M. Leopold Trouvelot, in Medford, Mass. A wind blew them off the windowsill where they were being warmed in the sun, and the rest is rather unfortunate history. With no natural enemies, like the Japanese beetle here in the United states and rabbits in Australia, the gypsy moth proliferated. The federal government has since spent more money to control the moth's damage than it has on any other insect-control program.
Whether they mate or not, the female moths lay their eggs between mid-June and early September on tree trunks or in leaf litter. The buff-colored mounds of eggs remain dormant through winter and fertile eggs hatch in late April and early May. At this time the tiny caterpillars, only 1/16th of an inch long, are readily airborne. This, in fact, is their principal means of migration. Moderate breezes transport them up to four miles distant, while hurricanes have transported the little worms for 20 miles.
The caterpillars grow to about 2 inches long, at which stage they are a fuzzy brown and black, with three light stripes transversing the back and five pairs of blue dots running along their backs, followed by six pairs of red dots. When the caterpillar stops feeding, it seeks a protected place in which to pupate. By mid-June the moths begin to emerge, the males first, followed a few days later by the females. While the male flies around, the female remains close to her pupation site, signaling her readiness to mate by giving off the scented sex attractant. It is at this stage that the moth's reproduction is disrupted by the synthetic pheromone.
Health-Chem Corporation has begun the manufacture of "Disrupt" pheromone flakes, for aerial application, and "Luretape," in two-inch-wide strips that can be fastened to the trunks of trees.
For further information on the USDA pheromone testing program contact: Dr. Ralph Webb, USDA, Building 470, Barc-East, Beltsville, Md. 20705, (301) 344-2269 ); or Dr. Agis Kydonieus or Dr. Alberto Quisumbing, Health-Chem Corporation, 1107 Broadway, New York, N.Y. 10010, (212) 691-7550.