The gypsy moth, Lymantria dispar, is one of North America's most devastating forest pests. The gypsy moth is known to feed on on the foliage of hundreds of species of plants in North America but its most common hosts are oaks and aspen. Gypsy moth hosts are located through most of the coterminous US but the highest concentrations of host trees are in the southern Appalachian Mtns., the Ozark Mtns., and in the northern Lake States.

Gypsy moth populations are typically eruptive in North America; in any forest stand densities may fluctuate from near 1 egg mass per ha to over 1,000 per ha. When densities reach very high levels, trees may become completely defoliated. Several successive years of defoliation , along with contributions by other biotic and abiotic stress factors, may ultimately result in tree mortality. In most northeastern forests, less than 20% of the trees in a forest will die but occasionally tree mortality may be very heavy.