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Gypsy Moth: Mating Disruption and Trapping

July 16, 2003

During this time of year, gypsy moths are in the adult stage, with the males flying around looking for females to mate with so that they will lay viable eggs. It is during this time that management strategies are implemented to prevent mating and determine the extent of infestation. This effort includes the distribution of pheromone flakes and placing traps in selected locations in front of a gypsy moth infestation.

Pheromone flakes. Use of pheromone flakes is a pest management strategy, mating disruption, in which the goal is to prevent adult male gypsy moths from mating with females. Pheromone flakes are typically applied after the caterpillars enter cocoons and emerge as adults. Flakes are applied by aircraft flying about 50 feet above the tree canopy- under the supervision of local authorities, the Illinois Department of Agriculture, and the United States Department of Agriculture.

Each flake is an elongated piece of plastic, about 1/8 inch long. They are applied at such a low rate that most people do not notice them. The flakes won’t remove the finish from automobiles or vinyl siding. The flakes release a synthetic version of the pheromone (disparlure) that the adult female gypsy moth releases to attract males. When the flakes are applied, so much pheromone is detected by the male gypsy moths, and coming from so many directions, that the male moths become confused. They typically sit, flutter their wings, and do not fly or mate. As a result, unmated females lay infertile eggs that do not hatch.

Pheromone flakes are only effective on relatively small populations (30 moths per trap or fewer than 10 eggs per acre), where chance encounters are unlikely. If populations are large, then females are present in numbers that males will find and mate with enough of them to keep the infestation high.

Traps. To determine the spread of gypsy moth, both federal and state regulatory agencies conduct comprehensive trapping programs. Pheromone traps are used in monitoring moth males (as males fly and females do not). These delta, or milk-carton, traps are cardboard, triangular-shaped, and 6 to 10 inches long and 3 to 4 inches wide per side. They may be lime green, orange-red, or brown. Traps are open at each end and sticky inside to capture any moth that enters. They are placed about 5 to 6 feet off the ground on tree trunks, poles, and other surfaces.

Traps are distributed in areas known to have gypsy moth and at the leading edge of an infestation to track the rate of spread. Traps are placed gridwise, depending on the likelihood of gypsy moths’ being present. In many areas, the traps may be placed more than a mile apart, such as in rural areas with few host trees. Where few gypsy moths are known to occur, traps are placed much closer to assist in locating infestations.

Traps are baited with a synthetic lure that mimics the pheromone released by the female gypsy moth to attract the male. Males enter the trap looking for a female producing the pheromone and get stuck. Collecting males makes it possible to determine if gypsy moths are present and provides a rough estimate of how numerous they are. In September, the male moths in traps are counted to determine the extent of the problem. 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 insecticide.

Do not disturb or move gypsy moth traps, and do not put out your own traps unless the area is generally infested. Capture of gypsy moths in traps does not necessarily mean that gypsy moths have become established. When many gypsy moths are detected in traps, an area may be quarantined. Moths other than gypsy moths may inadvertently enter the trap.

Gypsy moth is a federally quarantined pest, and the detection program involves trap tenders and other official personnel that have the right to trespass on any property. If the trap needs to be removed, call the phone number on the trap. Traps are generally removed in July or early August.

Author: Raymond A. Cloyd


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