In the northern part of the USA and in Canada, the caterpillars of Bruce spanworm, Operophtera bruceata(Hulst), attack a variety of hardwood trees, but sugar maple,aspen, and beech are the favored host trees. In areas where these favored host trees are numerous, moderate to severe defoliation will occur. For the past two years, the insect has caused widespread defoliation in the New England States. Several hundred thousand acres have been defoliated in 1982/1983 with 330,000 acres in Maine alone. Usually, outbreaks last about two years before the population collapses.