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Gypsy Moth: Part Two

July 3, 2002

This is the second article of a series in this newsletter on gypsy moth. The first article appeared in issue no. 3, published on May 8. Gypsy moth, Lymantria dispar, larvae are full-grown, and they are leaving the trees in northeastern Illinois to pupate. The pupae are dark brown, shell-like cases about 1 inch long, covered with hairs. They are primarily located in sheltered areas, such as tree bark crevices or leaf litter. Adult gypsy moth emergence generally begins the first week in July and continues into August. Males appear 4 to 5 days before the females. Following emergence, adult females locate themselves on tree trunks and release a sex pheromone or odor that attracts males. (In general, a pheromone is a chemical produced by one individual to affect the behavior of another.) Males fly around until they contact the pheromone, odor, which they can detect from a mile away. They then fly upward or upwind in a zigzag pattern to locate females and begin mating. After mating is complete, the females begin to lay eggs. Both sexes live only for about 7 to 10 days in the adult stages. Females in Illinois are unable to fly because they are heavily laden with eggs.

Eggs are normally laid from July through August. The egg mass is found close to where the mature female pupates, such as on tree trunks, on the undersides of branches, under bark or rocks, on buildings, on vehicles, or in debris. Females have white- to cream-colored wings, a tan body, and a 2-inch wingspan. Males, which are smaller than females, with a 1-1/2-inch wingspan, are dark brown and have feathery antennae. Both the adult female and male can be identified by the inverted V-shape that points to a dot on the wings.

In order to determine the spread of gypsy moth, both federal and state regulatory agencies conduct comprehensive gypsy moth trapping programs. Delta or milk carton traps (6 inches by 3 inches), which vary in color (green, orange, or brown), are placed about 5 to 6 feet off the ground on tree trunks or poles. They are distributed in areas that are known to have gypsy moth and at the leading edge of an infestation to track its spread. The traps are baited with a synthetic lure that attracts the male gypsy moth. Males enter the trap looking for a female producing the pheromone (scent), and they get stuck on its sticky interior. Each September, the number of male moths in traps is counted to determine the extent of the gypsy moth program. This provides a means to determine the potential infestation of an area and to decide if a quarantine should be implemented. The traps do not contain an insecticide. Do not disturb or move gypsy moth traps, and do not put out your own gypsy moth traps unless the area is generally infested. The capture of male gypsy moths in traps does not necessarily mean that gypsy moths have become established. When large numbers of gypsy moths are detected in traps, then an area may be designated as quarantined. Moths other than gypsy moths may inadvertently enter the trap; therefore, not all moths in the traps will be gypsy moths. Traps are generally removed in July or early August.

In some areas of northeastern Illinois, gypsy moth pheromone flakes have recently been applied. These are applied under the supervision of local authorities, Illinois Department of Agriculture, and the USDA. Each flake is elongate and about 1/8 inch long. These flakes are applied at such a low rate that most people do not notice them. The flakes release a synthetic version of the pheromone that the female gypsy moth releases to attract males to her for mating. When pheromone flakes are applied, so much pheromone is detected by the male gypsy moths coming from so many directions that the male moths become confused. They typically will sit and cower, flutter their wings, and do not fly or mate. As a result, the unmated females lay infertile eggs that do not hatch the following spring. Pheromone flakes are only effective on relatively small populations. If populations are large, females will be numerous enough that males will find and mate with enough of them to keep the infestation high.

Author: Donna Danielson of The Morton Arboretum Phil Nixon Raymond A. Cloyd


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