The Gypsy Moth (Lymantria dispar dispar) was introduced to North America from France by E.L Trouvelot in 1869 who had hopes of breeding a silk-spinning caterpillar that was more resistant to disease than the domesticated silkworm. Unfortunately, the caterpillars escaped into his backyard. About 10 years later, they began to appear in large swarms, and by the late 1880s they were causing severe defoliation in the area. Since then the Gypsy Moth has become one of the most destructive pests of hardwood trees in the eastern U.S.
The adult female moths emerged from their pupae this summer. With a life span of one week, the adults do not feed; they do, however, mate and lay eggs. Although the female moth has fully formed wings, she cannot fly. She emits pheromones that attract males, mates and then lays a cluster of 75-1,000 eggs close to where she pupated. She then covers them with buff-colored, hairlike setae from her abdomen, which serve as protection from predators and parasites. The eggs overwinter and hatch in the spring. The larvae have a voracious appetite and feed on more than 300 species of trees and shrubs.
Gypsy Moth egg masses appear to be prolific this fall, perhaps because there has been no significant wet weather to fuel the fungus (Entomophaga maimaiga) that feeds on the Gypsy Moth. While there are other natural controls for Gypsy Moths (birds, squirrels, mice, etc.) they don’t prevent infestations. If you wish to rid your woodlot of these caterpillars, you can remove the egg masses and pour boiling water over them. Scraping the eggs onto the ground is less effective as they can survive temperatures of 20°- 30°F. degrees below zero.
The Gypsy Moth was introduced into the United States in 1869 by a French scientist living in Massachusetts. Since then its range has expanded to include the entire Northeast south to North Carolina and as far west as Minnesota and Iowa. The consequence of the introduction of this insect is staggering. According to the U.S. Dept. of Agriculture, since 1980, the Gypsy Moth has defoliated close to a million or more forested acres each year. In 1981, a record 12.9 million acres were defoliated. This is an area larger than Rhode Island, Massachusetts, and Connecticut combined.
The Gypsy Moth females lay their eggs, usually on host tree trunks, in late summer. The eggs overwinter and hatch in the spring. Gypsy Moth caterpillars feed on a variety of species of shrubs and trees, with White Oak being their preferred host, metamorphose, mate and repeat this process. Usually their numbers are not overwhelming, but due to the weather conditions we’ve been experiencing, the caterpillar population has skyrocketed in some areas, especially in southern New England.
Conditions were very dry in parts of New England in May 2014 and May 2015, which impeded the growth of a certain kind of Japanese fungus (Entomophaga maimaiga) that keeps the Gypsy Moth caterpillar population under control. Without this fungus present to keep their numbers in check, Gypsy Moths have flourished. Although there was some rain this spring, there were many areas that did not get enough to benefit the fungus, and in these areas, trees are now stripped of their leaves. It is possible in places in southern New England to track the pattern of rainfall simply by looking at where trees are still in full leaf. Fortunately, the time has come for Gypsy Moth caterpillars to pupate, so most of this year’s destruction has already occurred. Here’s hoping for a rainy May next year.