Gypsy Moth

Lymantria dispar

Identification

Gypsy moth outbreaks occur in cycles, and when populations rise, they are serious defoliators of hardwood trees and shrubs. Otherwise healthy trees can generally survive several years of defoliation, and to track population outbreaks, Vermont Department of Forests, Parks, and Recreation conducts egg mass surveys across Vermont.

Older larvae (caterpillars) are brownish-gray, with tufts of hair on each segment and a double row of five pairs of blue spots, followed by six pairs of red spots, on the back. Mature larvae are from 1 1/2 to 2 1/2 inches long.

Adult male moths have light tan to brown wings marked with dark, wavy bands, and a 1.5 inch wingspread. Female moths are larger than males and generally white, with a wingspread of about 2.5 inches.

Signs and Symptoms

  • Young larvae chew small holes in leaves.
  • Older larvae feed on leaf edges, consuming entire leaves except for the larger veins and the midribs. The entire tree is often defoliated.

Biology

Origin

The gypsy moth accidentally escaped from the home and lab of Dr. Trouvelot, who brought the moths to Medford, MA to see if they could be developed into an alternative to the silk moth. Since then, gypsy moth has spread throughout the Northeast and well beyond.

Habitat

Gypsy moth is known to feed on over 300 trees and shrubs. Favored hosts include oak, apple, alder, basswood, birch, poplar, sweet gum, willow, and hawthorn. Less favored host species include hickory, maple, cherry, cottonwood, elm, black gum, larch, sassafras, and hornbeam. Some mortality even occurs in white pine. Many other plants may be fed upon.

Life Cycle

The gypsy moth goes through four stages of development—egg, larva (caterpillar), pupae (cocoon), and adult (moth). This species produces one generation per year.

Eggs: egg mass are laid in the fall and will typically contain between 500 and 1,000 eggs per mass. Egg masses are covered with buff or yellowish “hairs” from the abdomen of the female. The velvety egg masses vary in size but average about 1.5 inches long and .75 inches wide. Eggs start to hatch around early May in the northernmost United States.

Larvae: Older larvae (caterpillars) are brownish-gray, with tufts of hair on each segment and a double row of five pairs of blue spots, followed by six pairs of red spots, on the back. Mature larvae are from 1 1/2 to 2 1/2 inches long.

Caterpillars may remain in the lower forest canopy or, when in high populations, migrate upwards to the tree tops, where each one then spins down on a long silken thread. The caterpillars use a process of dispersal is known as “ballooning” and is somewhat common in species where the adult females do not fly. The caterpillars hang in the air, waiting for a strong wind to break the thread and carry them to a new location. This type of dispersal helps young larvae relocate to more favorable hosts. The caterpillars are voracious eaters, tend to feed at night, and gather in protected areas during the day. They may even gather in nests of the eastern tent caterpillar. Caterpillars stop feeding when they enter the pupal or cocoon stage. Gypsy moth caterpillars do not make silken webs or tents.

Pupae: Larva pupate in June-early July. Pupae are reddish dark brown, cylinder-shaped, and sparsely covered in hairs. Pupae are between 3/4 to 1 1/2 inches long and are attached to protected surfaces such as bark or rock crevices. Adults emerge in 10-14 days.

Adults: Adult male moths have light tan to brown wings marked with dark, wavy bands, and a 1.5 inch wingspread. Female moths are larger than males and generally white, with a wingspread of about 2.5 inches. Despite having larger wings, the female moths cannot fly. Neither sex feeds in the moth stage. Adults mate and lay eggs in August to September.

Ecological Threat

Young larvae chew small holes in leaves, while older larvae consume entire leaves except for the larger veins and midribs. The whole tree may be defoliated, resulting in reduced growth and loss of vigor, as well as reduced aesthetic, recreational, and wildlife values. If total defoliation is experienced over several years, mortality may result.

Management Options

Gypsy moth outbreaks occur periodically. Natural controls, including introduced insect parasites and predators, virus and fungal diseases, and adverse weather conditions, help control this pest.

Hand Removal: Egg masses can be removed from trees between August and May to reduce infestations in forthcoming years. Use a scraper to carefully remove the masses and submerge them into a container with soapy water or alcohol so that they can be destroyed (not onto the ground where they may still hatch).

Chemical Control:  Btk (Bacillus thuringiensis kurstaki) is a biopesticide can be applied by a registered pesticide application company or by homeowners who have carefully read application instructions. Btk is a product that affects the digestive system of caterpillars and should only be applied between May and early June, when gypsy moths are still in the larval stage and are are small (1/2 to 3/4 inch). Two spray applications are usually required for effective control. Application of Btk after mid-June is not an effective way to manage this pest.

Trapping: Caterpillars can be trapped using burlap. Start by wrapping an 18-inch wide strip around the tree at chest height. Tie a string around the center and fold the top portion down to form a skirt, with the string acting as a belt. Pick off the caterpillars daily and dispose of them by submerging them into a container with soapy water or alcohol.

Gypsy Moth Quarantine

If you are moving from a gypsy moth quarantine area to a non-quarantine area, you must inspect your outdoor house-hold items for the gypsy moth and remove all life stages of this destructive insect before you move.

Vermont Distribution

Gypsy moth is established in Vermont.

How You Can Help

Monitor for defoliation and egg masses throughout the season on high-risk trees. Inspect outdoor equipment, trailers, and vehicles before moving from a regulated area to an uninfested area and always buy and burn local firewood

Citations

Information

UMass Extension Fact Sheet

UNH Extension Fact Sheet

Forestry Images/Bugwood

Ontario's Invading Species Awareness Program Fact Sheet

University of Kentucky

USDA APHIS PPQ Fact Sheet

A Field Guide to Common Insect Pests of Urban Trees in the Northeast,  Vermont FPR

Images

John Ghent, Bugwood.org (488026, 0488025)

Tim Tigner, Virginia Department of Forestry, Bugwood.org (0886003, 0886002, 0886006)

Daniela Lupastean, University of Suceava, Bugwood.org (1121035)

Steven Katovich, Bugwood.org (1398103)

Karla Salp, Washington State Department of Agriculture, Bugwood.org (5562147)

William M. Ciesla, Forest Health Management International, Bugwood.org (5493133, 5493132)

Lacy L. Hyche, Auburn University, Bugwood.org (1430001)