Destructive gypsy moths (Lymantria dispar) were accidentally introduced into the United States in the 1860s in Boston, Massachusetts. They have been spreading westward ever since. Female adult gypsy moths will lay eggs under the bark of a tree, where they will overwinter. The grayish-brown caterpillars that emerge eat the leaves of many forest tree species, especially oaks and aspens.
Newly hatched caterpillars hang from the trees on threads of silk. The blowing wind easily transports them to nearby trees where their feeding continues. The larvae are nocturnal, feeding at night and hiding under bark during the day. When they eat, they will nearly defoliate a tree. Healthy trees will produce new leaves but run the risk of being attacked again. If a tree is defoliated two years in a row, the tree will almost always die. Their populations are quickly growing and they are spreading across the oak-hickory forests of eastern and southeastern Ohio.
Because of increasing gypsy moth populations in northeastern Ohio, the State and Federal Departments of Agriculture placed a quarantine on the area in 1987 to limit the spread of the insect. They reached defoliating levels in 1993. In 1994, one hundred acres had been affected. In 1996, fifty thousand acres of Ohio forests had been damaged by gypsy moths. The USDA Forest Service estimates that gypsy moths are spreading in deciduous hardwood forests at a rate of approximately thirteen miles per year.
In addition to aerial applications of an insecticide derived from the naturally-occurring bacterium, Bacillus thuringiensis, commonly know as BT, researchers have recently discovered a natural gypsy moth fighter. It is a fungus called Entomophaga maimaiga, or Em. This fungus first appeared in Trumbull County, Ohio in 1993. In Ohio, and other eastern states, Em has proven effective in killing gypsy moth caterpillars when they come in contact with its spores in the spring. Once infected, the gypsy moth caterpillars die within seven to ten days. A benefit to using the fungus is that it appears to affect only the gypsy moth and not other butterfly or moth species. Research is still being done on Em and gypsy moths. Other predators of the gypsy moth larvae include deer mice and shrews.
Over the last twenty years, federal and state agencies have sprayed millions of acres in the United States with pesticides and practiced many other methods of control in hopes of killing, or at least controlling the devastation level, of the gypsy moth.