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liage eaten, the number of successive annual defoliations, the occurrence of refoliation, weather, and subsequent attacks by other insects or disease-causing organisms.
Usually a tree can lose up to half its leaves without losing much vigor, but heavier or repeated defoliations and the refoliation which follows, deplete food reserves significantly. Trees stressed by defoliation become more susceptible to damage from adverse weather, insects, fungi and other organisms.
Gypsy moth outbreaks usually result in two or sometimes three successive years of heavy defoliaton before virus disease or a combination of natural agents reduces the larval population to low levels. Local tree mortality following two successive years of heavy defoliaton can vary from 5 percent to 80 percent.
Experience has shown that some forests are more likely to be defoliated than others. Susceptible stands of trees have a preponderance of white oaks and an abundance of sites (refuges) suitable for resting caterpillars, pupation and egg lay
90.7%