Instead, with the escape of these insects from his home, North American forests acquired a major insect problem that has grown in significance. Damage to U.S. forests is measured in productivity, use, and aesthetic value losses. The insect has spread from the northeast coast to as far west as Wisconsin and as far south as North Carolina. Egg masses are often transported by cars or on other outdoor equipment that, when moved from one location to another, result in the invasion of new areas by the gypsy moth.
High winds can also blow the newly hatched larvae long distances.
Gypsy moths can defoliate large areas of forest, preferring oak and aspen stands. If populations are large enough, and trees are defoliated in several successive years, the stress of defoliation in combination with other environmental stresses may kill the trees. European gypsy moths were introduced into the United States without their normal compliment of predators, parasites, or pathogens. Some of these natural enemies, including a virus and a fungus, were introduced later and have had important suppressive effects on the gypsy moth. We are looking at a group of protozoan pathogens called microsporidia.