It is a tree defoliating insect and was introduced to the United States in 1860 by E. Leopold Trouvelot    
Gypsy moth is capable of defoliating millions of acres of forest in a single year.
The larva or caterpillar is the damaging stage as it eats the leaves of trees in the spring.Gypsy moth larvae can consume as much as one square foot of leaves per day.. Consistent or repeated defoliation over several years can have devastating effects, often leading to tree stress and death.
The gypsy moth is affecting north america the most right now laying their eggs on the leaves of the apple, speckled alder, basswood, gray and river birch, hawthorn oak, poplar, and willow. Less desired but still attacked are black, yellow, and paper birch, cherry, cottonwood, elm, black gum,hickory, horn beam, larch, maple and sassafras

• In wooded backyards, or in yards where lawns and forests meet, an attempt should be made to keep the forest floor surface as natural as possible (fig. 41). Because oaks thrive under acid soil conditions, removal of their organic acid-rich leaf litter can be harmful. Layers of natural leaf litter help prevent drying out surface soil layers that contain the bulk of the tree’s feeder roots and provide a natural habitat for predators such as mice and shrews that prey upon gypsy moth larvae and pupae.

• Growth conditions for isolated trees planted on lawns can be enhanced by encircling them with mulch or ground cover plants (when practical) out to an area delimited by the outer branches. A dense grass layer over feeder roots causes severe competition for moisture and nutrients. Applications of lime or weed killers around forest trees can seriously damage shallow tree roots.

• In times of drought, stressed individual trees can also benefit from watering, fertilizing, and judicious pruning to thin the tree tops and reduce moisture demands on the roots.