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Gypsy moth

The gypsy moth (Lymantria dispar) is one of the most destructive insect pests threatening our forests, trees and shrubs.  It was introduced more than 100 years ago, and has slowly munched its way west and south from its original infestation point in Massachusetts.

The gypsy moth is native to Europe and Asia and is the major introduced pest of eastern United States hardwood forests. The gypsy moth is found mainly in the temperate regions of the world, including central and southern Europe, northern Africa, central and southern Asia, and Japan. The gypsy moth was originally introduced into Medford, Massachusetts in 1869 by Leopold Trouvelot, a French astronomer with an interest in insects.

Trouvelot wanted to develop a strain of silk moth that was resistant to disease as a part of an effort to begin a commercial silk industry. However, several gypsy moth caterpillars escaped from Trouvelot's home and established themselves in the surrounding areas. Surprisingly, it wasn't until 20 years later that the first outbreak occurred.

Despite all control efforts since its introduction, the gypsy moth has persisted and extended its range. In the United States, the gypsy moth has rapidly moved north to Canada, west to Wisconsin, and south to North Carolina. Gypsy moth caterpillars defoliate millions of acres of trees annually in the United States.

Gypsy moth life cycle

The gypsy moth develops in four stages in its life-cycle: Egg, Larva, Pupa, and Moth. The gypsy moth has only 1 generation per year.  It over winters in the egg stage in tan-colored masses.  Hatching generally occurs in late April or early May, just as tree leaves are emerging.  The newly hatched larvae are 1/8" long, hairy, and mostly dark brown to black.  They climb to the tops of the trees and feed on leaves.  The larva spins a thread and uses wind currents to balloon from tree to tree.  This is the main way gypsy moths disperse.

The gypsy moth survives the winter as eggs laid in masses of up to 1,000 eggs or more. Eggs hatch in April or early May into tiny (about 1/4" long), black, hairy caterpillars.

Newly hatched caterpillars climb into tree canopies and begin feeding. If their first tree is not to their liking, they will produce a silken thread, which carries them like a balloon on wind currents to more suitable hosts. The caterpillars continue feeding throughout the rest of the spring, undergoing five to six molts. The first three caterpillar instars have black heads and generally black bodies. By the fourth instar, the caterpillars are about one inch long, have mottled brown heads, bodies covered with black and brown hairs, and a series of five pairs of blue spots followed by five pairs of red spots on the tops of the bodies.

The greatest feeding damage is done by older caterpillars during the last two weeks of June, sometimes making it appear as if trees are stripped of leaves practically over night. After they have completed feeding in late June or early July, caterpillars enter the pupal stage from which adult moths emerge after 10 — 14 days.

Adult moths do not feed. The brownish male moth flies about during the day in search of females with which to mate. Whitish females do not fly, but attract males to them by means of a chemical 'perfume', or pheromone. Egg masses deposited during mid- to late July will hatch the following spring, completing the life cycle.

Controlling gypsy moth infestations

There are several ways to control gypsy moth. In small populations, it may be easiest to destroy egg masses that are found on buildings, trees, etc. To destroy the egg mass, either crush the eggs or place them in a bucket of kerosene or soapy water. Burning the egg mass will also kill them. Simply picking the egg masses off and dropping them on the ground will not kill them. Be careful when handling the egg masses because the hairs that cover the egg masses may cause an allergic reaction.

Various control measures are available for use against the gypsy moth larva; however 2 commonly used insecticides are Bt (Bacillus thuringiensis) and diflubenzuron or Dimilin. Bt is a naturally occurring disease that only kills caterpillars, and Dimilin is a chemical that interferes with gypsy moth growth and eventually kills the caterpillar.