Biology
larvae emerging from egg mass
M. Zubrick, Forest Research Institute - Slovakia,
Bugwood.org
The gypsy moth has one generation per year. The time of year at which different life stages are present is determined by temperature. In general, eggs hatch in Virginia from early April to early May - about the time oak leaves begin to develop. Newly hatched larvae (caterpillars) climb high into trees and are dispersed by the wind. While larvae can be carried a mile or more on wind currents, most land less than 200 meters from their hatching location. This “ballooning” by first instar larvae is the primary means of natural dispersal. As the larvae mature they undergo a series of growth stages called instars; males typically have five instars while females have six. Young larvae feed during the day and rest in the tree canopy overnight. Older larvae feed at night, crawling down the tree during the day to seek sheltered resting sites. The exception to this pattern is in high populations when larvae feed continuously until all foliage is removed and then move in search of new food sources. Although feeding activity of young larvae may not be noticed, older larvae are voracious feeders and can grow to a length of over 2.5 inches. It is estimated that a gypsy moth caterpillar consumes about one square meter of foliage in its lifetime.
gypsy moth larvaConnecticut Agricultural Experiment Station Archive,
Bugwood.org
Gypsy moth larvae are quite hairy. Early instars are dark in color with orange splotches on the back. By the 4th instar, larvae have distinguishing pairs of blue and red dots along their backs. They sometimes are confused with other defoliators such as eastern tent caterpillar, forest tent caterpillar, and tussock moth. The gypsy moth does not form large silken webs and has entirely different behavior and seasonal development from these insects. Fairfax County has a description of these insects compared to gypsy moth.
pupae, female on left
After 4 to 6 weeks, mature larvae develop into pupae from which the adults emerge approximately two weeks later. The female moth does not fly; she releases a pheromone that the male detects and uses to locate the female for mating. After mating, the female lays an egg mass containing from a few hundred to nearly one thousand eggs. These eggs are the overwintering stage of the insect. Egg masses usually are laid on tree trunks, the underside of branches, or rocks around the base of the tree. The egg masses are buff colored and covered with hairs from the female's abdomen. Adults do not feed and live only a few days after emergence and mating.
gypsy moth male (l) and female (r)
J.H. Ghent, USDA Forest Service, Bugwood.org
Gypsy moths will feed on over 300 tree species, but its preferred hosts include oak, aspen, willow, birch, apple, and basswood. Young larvae are much more discriminating than older ones, which will feed readily on less preferred species such as maple, hickory, elm, and many conifers. Usually, these less preferred species are fed upon only when insect populations are high and preferred food sources become scarce. Some trees are never fed upon, the classic example being tulip (yellow) poplar.
Calendar
The image below shows when the various gypsy moth life stages occur in Virginia. It also notes the corresponding control activities.
Life Cycle Calendar