Gypsy Moth
The gypsy moth originally evolved in Europe and Asia and has existed there for thousands of years. In either 1868 or 1869, the gypsy moth was accidentally introduced near Boston, MA by E. Leopold Trouvelot, a French naturalist who was experimenting with silkworms. It is now found throughout all northeastern states and bordering areas of eastern Canada. Spot infestations have been found in the Midwest. Every year, isolated populations are discovered beyond the contiguous range of the gypsy moth but these populations are eradicated or they disappear without intervention. It is inevitable that the gypsy moth will continue to expand its range in the future.
Gypsy moths prefer oaks (white, chestnut, red), apple, basswood, gray birch, hawthorn, poplar, beech, and willow, but they may attack hardwoods and conifers as well. Older larvae will feed on conifers. In outbreaks, gypsy moths will feed on almost anything including many ornamentals, vegetables and even houseplants.
Description and Life Cycle
The heavy, flightless 2-inch long female moth is white with a yellow to buff abdomen and irregular blackish bands on the forewings. The male is smaller than the female and is mottled brown and black. The male is active during the day, searching for females. Fully-grown caterpillars are 1½ to 2½ inches long, hairy, and vary from slate gray to a sooty or dusky color. They have five pairs of blue spots followed by six pairs of red spots along the back, which distinguish the gypsy moth caterpillar from other defoliating caterpillars. The head capsule is black and gold.
The female lays egg masses on trees, stones, or fences, under loose bark, and in other protected places in mid- to late summer. The eggs overwinter, hatching in early May. The newly-hatched caterpillars spin silken threads on which they may be wind borne for long distances. In mid-summer, mature caterpillars spin a few strands of silk and pupate within a dark brown pupal case. The moths emerge in one to three weeks. There is one generation a year.
Damage
Despite over 150 years of presence in North America, researchers are still at a loss to explain and predict the extent of the changes in forest vegetation likely to takeplace through gypsy moth disturbance. A major concern is the potential loss of economically critical and ecologically dominant oak species. Most studies of forest compositional changes with gypsy moth defoliation indicate that less susceptible species will dominate the forest, so forests may have fewer gypsy mothproblems in the future.
Vigorous hardwoods can usually survive one complete defoliation, but a similar attack may be fatal to conifers. Repeated defoliation of hardwoods will reduce tree vigor to a point where other factors or pests may cause death. Tree losses have been noted after one to two years of complete defoliation during drought periods, particularly on poor sites. The aesthetic, recreational, and watershed values of forest, park, and ornamental trees can be seriously threatened by the gypsy moth. The hairs of the young larvae often cause a skin rash on humans.
Management
Natural: A variety of natural agents are known to kill gypsy moths in nature. These agents include over 20 insect parasitoids and predators that were introduced over the last 100 years from Asia and Europe. Small mammals are perhaps the most important gypsy moth predator, especially at low population densities. Birds are also known to prey on gypsy moths but at least in North America this does not substantially affect populations. A virus usually causes the collapse of outbreak populations and an entomopathogenic fungus species has caused considerable mortality of populations in North America. Gypsy moth infestations are also regulated by other factors, most important of which is stand composition (i.e., hosts). Gray birch and chestnut/white oak stands are favored for initial buildup. Persistently low winter temperatures (-20oF) may cause egg mortality in unprotected situations.
Cultural Control: Stressed trees are more vulnerable to damage from defoliation. Keep trees in good health and vigor. Maintain good soil nutrient and moisture relationships by mulching, watering, judicious green wood pruning, and fertilizing when needed. Replace susceptible species with resistant species. Create mixed plantings with species that are not generally hosts.
Quarantine: It is very important that gypsy moths not be spread to areas outside of the northeastern states. Gypsy moths are commonly transported in the egg or pupal stage on home and yard objects, mobile homes, trailers, etc. There is a USDA-APHIS regulation prohibiting the transportation of gypsy moth-infested items.
Chemical: Over the last 25 years, several millions of acres of forest land have been aerially sprayed with pesticides in order to suppress outbreak gypsy moth populations. Though some areas are treated by private companies under contract with land owners, most areas are sprayed under joint programs of state governments and the USDA Forest Service.
Adapted from G.R. Nielson, University of Vermont Extension, 1999; USDA Forest Service, 2003
