General Info

General Information About the Gypsy Moth

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 caterpillars hatch from eggs during bud-breaking which occurs in mid-spring. Although the caterpillars are capable of feeding on over 300 species of trees and shrubs they prefer oaks. The male and female caterpillars typically pass through five and six instars (stages), respectively, before they enter the pupal (resting) stage in early to mid-summer (June-July). They remain in the pupal stage for approximately 2 weeks and the male moths emerge one or two days before the females. The adult male and female gypsy moths are easily distinguished from one another; the males are brownish-gray, whereas the females are white with black markings and slightly larger. Unlike the males, the females are incapable of flight. Note that the newly introduced Asian gypsy moth females can fly!

After emerging from the pupal stage, female moths emit a pheromone (chemical) which attracts males from moderate distances and mating then occurs. The females then lay oval-shaped egg masses which are covered with hairs from her body. The buff-colored egg masses contain 100 to 1,500 eggs and are laid on the underside of tree limbs, bark, rocks, and structures including buildings, campers, mobile homes, etc. Long distance spread of the gypsy moth occurs when egg masses are unknowingly transported from infested areas on vehicles. Short distance spread results when small caterpillars are blown by the wind, a process known as "ballooning".

Repeated defoliation stresses trees and can lead to death. During outbreaks in residential areas gypsy moth caterpillars are an extreme nuisance. Trees lose their foliage, caterpillars crawl everywhere, and their droppings rain from the trees. When disease kills large numbers of caterpillars, as often occurs, the stench is overwhelming. In some cases, people develop an allergy to the hairs of the gypsy moth caterpillars.

Various control measures are available for use against the gypsy moth; however two 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.