Gypsy Moth

Identification

Gypsy moth (Lymantria dispar) larvae are 1-2 inches in length when fully grown. They are grayish in color with hair-like structures along the entire body. Larvae can best be identified by the five pair of blue and six pair of red dots along the back of the body. Adult moths have approximately 1 inch (male) or 2 inches (females) wingspans. Males are light tan with wavy dark bands across the forewings. Females are nearly white with bark bands across the forewings. Females are flightless. Male antennae have a feathered appearance. Female antennae are long and thin without the feathery appearance.

Biology

Gypsy moth has one generation per year. Eggs hatch in late spring (April-May). The small, young larvae ascend the tree, trailing a silken thread. The larvae disperse via “ballooning” when the wind catches the silken thread and transports the young larvae (BROKEN-LINK SAMAB 1996). When larvae land on a favorable host, they begin to feed upon the foliage. The larvae will pass through 5-6 molt stages, called instars, as they feed upon the leaves. The caterpillar stage lasts around six weeks. After the larvae complete their development they pupate for about two weeks. The adults emerge in mid-late summer.

The adults do not feed and are very short-lived (2-4 days). Females do not fly but give off a strong pheromone that attracts the flying males. After mating the females lay 75-1000 eggs in masses. Since the females are flightless dispersal of this species is restricted to the ballooning stage of the larvae and any accidental transportation of larvae or eggs by humans.

History

Gypsy moth was first introduced into the United States in the late 1860s in Massachusetts (Ghent 1994). By 1906, gypsy moth had spread into other northeastern states. The infestation had spread as far as New York by 1945. Gypsy moth continued to increase its range south and westward, and by the 1980s the leading edge of the infestation reached the northern bounds of the southern Appalachians. Between 1984 and 1994, more than 4 million acres in Virginia and more than 1 million acres in West Virginia were defoliated due to gypsy moth (BROKEN-LINK SAMAB 1996). Several small infestations, likely resulting from long-distance transport by humans, have been detected and eradicated throughout the southern Appalachians. While the southward and westward expansion of gypsy moth’s range continues, efforts are continually being made to identify and eradicate new infestations in an attempt to slow the spread.

Hosts

While gypsy moth can feed upon many different species their preferred hosts are oaks (Quercus spp.). Other species that readily serves as host include (Ghent 1994):

• Apple (Malus spp.)
• Basswood (Tilia americana)
• Birch (Betula spp.)
• Mountain-ash (Sorbus americana)
• Sweetgum (Liquidambar styraciflua)
• Willow (Salix spp.)
• Eastern hophornbeam (Ostrya virginiana)
• Serviceberry (Amelanchier arborea)
• With-hazel (Hamamelis virginiana)

Impact

Gypsy moth caterpillars damage trees by feeding upon the leaves, leading to defoliation. Excessive defoliations can lead to reduction in growth, crown dieback, and tree mortality (Ghent 1994). Trees often regrow their leaves after a spring defoliation event, which diminishes their energy reserves, making the tree more susceptible to drought, further insect attacks, diseases, and other stress factors. Site attributes and tree condition affects the susceptibility of trees to defoliation. Healthy trees can withstand several years of defoliation before any dieback occurs (Ghent 1994).