Author:Joseph LaForest, University of Georgia
- The gypsy moth, Lymantria dispar, currently established in North America, is a European native that was accidentally introduced into New England in the late 1800's during an attempt to rear an alternative silk producing insect.
- Life Cycle
- The gypsy moth has one generation per year. From June to mid-July, the female attaches buff-colored, velvety egg masses to sheltered places on outdoor objects. These masses allow the insect to overwinter and may contain up to 1,000 eggs. Masses are also embedded with female abdominal hairs that may act as an allergen. The eggs hatch in April or May. Young larvae chew small holes in leaves, while older larvae consume entire leaves except for the larger veins and midribs. The whole tree may be defoliated, resulting in reduced growth and loss of vigor, as well as reduced aesthetic, recreational, and wildlife values. If total defoliation is experienced over several years, mortality may result. The older caterpillars are 1.5–2.5 in. (3.8-6.4 cm) long and are easy to identify by the tufts of hair on each segment and the pattern of blue and red dots on their backs. The gypsy moth pupates in dark brown pupal cases located in sheltered locations. Male gypsy moths have a 1.5 in. (3.8 cm) wingspread with light tan to brown wings marked with wavy, dark bands across the forewing. Females are white, larger than males with a wingspread of 2.5 in. (6.4 cm), and flightless. There is also an Asian strain of the gypsy moth (AGM) that was identified in 1991. AGM has a much broader host range and the females are active fliers due to their larger wingspan. These factors would allow AGM to spread much faster than the European strain and be even more damaging.
- L. dispar's current range extends from Maine to North Carolina and west across Pennsylvania and into Virginia, West Virginia, Ohio, Michigan, and Wisconsin. Spread occurs as a result of both natural flight of the moth and the attachment and transport of egg masses on vehicles. Gypsy moth is known to feed on over 300 trees and shrubs. Favored hosts include oak, apple, alder, basswood, birch, poplar, sweet gum, willow, and hawthorn. Less favored host species include hickory, maple, cherry, cottonwood, elm, black gum, larch, sassafras, and hornbeam. Some mortality even occurs in white pine. Many other plants may be fed upon.
- Control Efforts
- Use of tanglefoot or placement of burlap bands around the trunk of the tree can be used to trap larvae and can afford some protection to individual ornamental trees. Natural controls, including introduced insect parasites and predators, virus diseases, and adverse weather conditions, help control the gypsy moth. Chemical and microbial insecticides have been used, primarily in urban and recreation areas.
Gypsy moth egg masses were brought to the Boston area in 1869 from France for experimental crossbreeding with the silkworm. Unfortunately some of the larvae escaped and became established on the local vegetation. The insect has now spread throughout New England, the Mid-Atlantic States, southeastern Quebec, and central Michigan. Scattered infestations have been reported along the East Coast to Florida to as far as California. The gypsy moth is considered one of the most important pests of red and white oaks in the Northeast. It causes widespread defoliation, resulting in reduced growth, loss of vigor, mortality, and reduces aesthetic, recreational, and wildlife values. Gypsy moth larvae can be a serious nuisance in urban and recreation areas.
The European gypsy moth has more than 250 known host plants which include most hardwoods and any conifer. oak is prefered followed by apple, birch, boxelder, hawthorn, linden, poplar, sweet gum, willow and basswood. Other potential hosts include hickory, maple, cherry, cottonwood, elm, blackgum, larch, sassafras, and hornbean. As availability of food decreases, larvae will switch from prefered hosts to less paletable plants.
Older larvae are brownish-gray, with tufts of hair on each segment and a double row of five pairs of blue spots, followed by six pairs of red spots, on the back. The head has patches of yellow markings. Mature larvae are from 1 1/2 to 2 1/2 inches (40 to 60 mm) long. Adult male moths are dark brown, with wavy dark bands across the forewings. Females are white and cannot fly. The distinctive felt-like, tan egg masses may be seen on bark, branches, and in other sheltered locations throughout the winter. In early May, shot hole damage to leaves by young larvae is apparent. Large larvae consume all but the larger veins and midvein. They tend to feed at night, and gather in protected areas during the day. They may even gather in nests of the Eastern tent caterpillar. The entire tree is often defoliated. The male moth has a wingspan of about 37 mm (1.4 in) and is dark brown with black bands across the forewings. The female is white with variable black bands across the forewings and her abdomen is covered with buff or light-brown hairs. She is larger, with a wingspan of about 50 mm (2 in.), but rarely flies.
There is one generation per year, with winter spent in the egg stage. Eggs hatch at the time that serviceberry (Amelanchier spp.) begins to bloom. Larvae emerge in late April or early May from overwintering eggs and feed through June and into early July. Newly hatched larvae move from the egg masses toward the top of the tree. When disturbed, larvae will spin down on silken threads; this behavioral trait, along with a small body size and long body hairs, makes this stage very susceptible to airborne dispersal by the wind. This type of dispersal can spread an infestation up to 1.6 (1 mile) in flat terrian or more than 7 km (4.4 mile) in hilly topography. During the day, the larvae congregate in sheltered locations. If trees are completely defoliated before the larval stage is finished, larvae leave the bare trees to search for another food source. This short distance movement can become a nuisance in wooded residential areas. The homeowner becomes acutely aware of the wandering larvae, which fall into swimming pools and climb all over lawn furniture, patios, and shrubbery. Pupation takes place in sheltered locations on tree trunks or branches, or under other objects such as rocks and picnic tables. The pupa is dark reddish brown with a sprinkling of reddish hairs. Adults emerge about 2 weeks later to mate and lay eggs in July and August. The heavier white females do not fly but do crawl a short distance from the pupation site, mate, lay eggs and die. Females deposit egg masses containing 75 to 800 eggs that are covered with buff to light-brown hairs from the female's abdomen. Some people exposed to the hairs in the egg masses can become sensitized to them and develop an alergic reaction. Most egg masses are deposited under rocks and on tree trunks, limbs, houses, picnic tables, trailers, campers, mobile homes, cars, and other sheltered places. The smaller brown males are very active fliers and often become a nuisance in infested areas.
Gypsy moth outbreaks occur periodically. Egg mass counts can be used to predict spring infestation levels, with 10 or more masses per tree indicating that severe defoliation may follow. As egg masses remain somewhat intact for several years, be sure that the count includes only viable eggs. Viable eggs should be firm to the touch and "pop" when crushed. Should you desire to provide relief by scraping off egg masses, be sure to scrape them into a container so that they can be destroyed, not onto the ground where they may still hatch.
Pheromone traps are also used to detect the presence of new infestations. While destroying the adults in the trap may be satisfying, this is not an effective control technique since only males are able to fly to the traps and the traps are not capable of trapping enough individuals to effect the size of the population.
Use of tanglefoot or placement of burlap bands around the trunk of the tree can be used to trap larvae and can can afford some protection to individual ornamental trees.
Natural controls, including introduced insect parasites and predators, virus diseases, and adverse weather conditions, help control the gypsy moth. Bacillus thuringiensis applied to very young larvae in May can provide good control. Diseases and starvation become important control agents when populations are high.
Chemical and microbial insecticides have been used, primarily in urban and recreation areas, to prevent defoliation and the nuisance effects of the pest. Residual insecticides are necessary if applications are made after mid- to late-May. Any materials applied directly to the bark may be toxic to thin-barked trees.
There is also an Asian strain of the gypsy moth that was identified in 1991. It has a much broader host range including larch, alder and some evergreens. The females are active fliers due to their larger wingspan and can fly long distances (up to 20 miles). These factors would allow it to spread much faster than the European strain and be even more damaging. This strain was detected in the Pacific Northwest in 1997 and eradication efforts were pursued through 1999.
These materials may be used as long as the original author is given credit.
- ↑ Hanson, T., and E. B. Walker. 2002. Field guide to common insect pests of urban trees in the Northeast. Waterbury, VT: Department of Forests, Parks and Recreation. 1.0 1.1 1.2 1.3 1.4 1.5
- ↑ Roberts, E.A. Gypsy Moth in Virginia: An Update. Publication Number 444-750, Posted February 2001. Virginia Cooperative Extension. http://www.ext.vt.edu/pubs/entomology/444-750/444-750.html 2.0 2.1
- Johnson, W.T. and Lyon, H.H. 1991. Insects That Feed on Trees and Shrubs . 2nd edition. Cornell University Press. p 138-141
- Martineau, R. 1984. Insects Harmful to Forest Trees. Agriculture Canada Government Publishing Centre, Supply and Services, Ottawa. p 112-114
- Drooz, A.T. 1985. Insects of Eastern Forests. USDA Forest Service Miscellaneous Publication 1426. p 229-233