Lymantria (Porthetria) dispar (L.) The gypsy moth (image) was
introduced into this country from Europe in 1869 and occurs
generally throughout most of Northeastern America. During
favorable conditions for the gypsy moth, outbreaks may appear
suddenly and may continue for two to five years in any one
location. NATURAL CONTROL factors such as starvation, disease,
parasites and predators eventually combine to bring about a
sudden collapse of these outbreaks. Prolonged sub-zero
temperatures can also kill the overwintering eggs that are not
insulated under a snow cover. Most healthy hardwoods can usually
withstand one to several years of severe defoliation by the
gypsy moth. However, white oak is very vulnerable to this pest
and hemlock and pine can be killed in one season when 90 to 95%
of the foliage is consumed. In hardwood stands the understory
and partially-shaded trees (weaker trees) are the first to be
killed by repeated defoliation. When present in large numbers
the wandering caterpillars and their droppin