Lymantria dispar
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Authors: Trish Hanson and E. Bradford Walker, Vermont Department of Forests, Parks and Recreation; E.A. Roberts, Virginia Tech
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Hosts
The European gypsy moth has more than 250 known host plants but prefers oak. Other hosts include apple, birch, boxelder, hawthorn, linden, poplar, sweet gum, and willow.
Evidence
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, which are hairy and gray with five pairs of blue dots and six pairs of red dots, 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.
Life cycle
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, and larvae feed until July. Gypsy moth larvae tend to feed at night. Feeding by later instar larvae will consume all but the larger veins and midribs. Pupation takes place in sheltered locations on tree trunks or branches, or under other objects such as rocks and picnic tables. Adults emerge about 2 weeks later to mate and lay eggs. The heavier white females do not fly but do crawl a short distance from the pupation site, mate, lay eggs and die. The smaller brown males are very active fliers and often become a nuisance in infested areas.
Population cycles
Gypsy moth is an outbreak pest. It can remain at low levels for several years and then undergo large population increases in a very few years. Unless areas are actively monitored even moderate gypsy moth populations can exist unnoticed. Thus, population outbreaks sometimes appear to occur in only one or two years. Although these cycles are influenced by numerous factors, the low populations are believed to be the result, at least in part, of a gypsy moth disease caused by the fungus Entomophaga maimaiga. This fungus was introduced into the U.S. as a possible control agent in the early 1900s but never appeared to become established. However, it was "rediscovered" in 1989 in New England and has since been found throughout a large portion of the generally infested area. Gypsy moth populations are also affected by another disease caused by a virus. The virus is the usual cause of mortality in high populations, whereas E. maimaiga serves as a control agent at both low and high pest densities.
Management
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. Bacillus thuringiensis applied to very young larvae in May can provide good control. Residual insecticides are necessary if applications are made after mid- to late-May. Although barrier bands can afford some protection to individual ornamental trees, they should be used with great caution. Any materials applied directly to the bark may be toxic to thin-barked trees. Diseases and starvation become important control agents when populations are high.
Asian gypsy moth
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.
References
- Drooz, A.T. 1985. Insects of Eastern Forests. USDA Forest Service Miscellaneous Publication 1426. p 229-233;
- 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.
- 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;
- Roberts, E.A. Gypsy Moth in Virginia: An Update. Publication Number 444-750, Posted February 2001. Virginia Cooperative Extension.
- Rose, A.H. and Lindquist, O.H. Revised by Syme, P. 1994. Insects of Eastern Spruces, Fir and Hemlock . Canadian Forest Service Publication. p 141 and 144-145.
- USDA APHIS PPQ. Asian Gypsy Moth. April 2003
Image Gallery
 Photo by USDA APHIS PPQ Archive, USDA APHIS PPQ, Bugwood.org |
 Photo by Jim Occi, BugPics, Bugwood.org |
 Photo by Connecticut Agricultural Experiment Station Archive, Connecticut Agricultural Experiment Station, Bugwood.org |
 Photo by Hannes Lemme, , Bugwood.org |
 Photo by Mark Robinson, USDA Forest Service, Bugwood.org |
 Photo by USDA APHIS PPQ Archive, USDA APHIS PPQ, Bugwood.org |
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Presentation Materials
These materials may be used as long as the original author is given credit.
Asian Gypsy Moth with file information
Importance
The gypsy moth, which came from France, is considered one of the most important pests of red and white oaks in the Northeast. It has spread southward into Virginia and is continuing to move south. Favored host species are oak, apple, alder, basswood, birch, poplar, sweetgum, willow, and hawthorn. Less favored are hickory, maple, cherry, cottonwood, elm, blackgum, larch, sassafras, and hornbean. Some mortality even occurs in white pine. 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.
Identifying the Insect
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. 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.
Identifying the Injury
Young larvae chew small holes in leaves. Older larvae feed on leaf edges, consuming entire leaves except for the larger veins and the midribs. The entire tree is often defoliated.
Biology
Larvae emerge in late April or early May from overwintering eggs and feed through June and into early July. Pupation occurs in sheltered places and lasts 2 weeks. Adults emerge in July and August. Females deposit egg masses (100 to 800 eggs) covered with buff-colored hairs, under rocks and on tree trunks, limbs, houses, picnic tables, trailers, campers, mobile homes, cars, and other sheltered places.
Control
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, to prevent defoliation and the nuisance effects of the pest.
Gallery
  Photo by John H. Ghent, USDA Forest Service, Bugwood.org |  Photo by John H. Ghent, USDA Forest Service, Bugwood.org |  Photo by John H. Ghent, USDA Forest Service, Bugwood.org |
References
Insects and Diseases of Trees in the South. 1989. USDA Forest Service - Forest Health Protection. R8-PR16. 98 pp. Taken from http://fhpr8.srs.fs.fed.us/forstpst.html
from
Talerico, R. L., 1978. Major hardwood defoliators of the Eastern United States. U.S. Dep. Agric., Home and Garden Bull. 224.
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. Hosts include most hardwoods and any conifer that might be mixed in with the more favored hosts of oak, gray birch, and poplar. Yellow-poplar and ash are usually avoided, but in outbreak situations the larvae will eat just about anything.
In late summer, eggs are deposited in masses (fig 13) containing 75 to 800 eggs that are covered with buff to light-brown hairs from the female’s abdomen (fig 14). These hairs insulate the eggs from low winter temperatures. Most egg masses are deposited on the trunks and limbs of trees, but they can also be found under stones, inside hollow trees and stumps, on leaves, and on various manmade objects. Eggs hatch in late April or early May, usually about the time the oak leaves are expanding.
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.
A full-grown larva is 40 to 60 mm (1.5 to 2.4 in) long. The head has patches of yellow markings; the body is a dusty or sooty black with tufts of hair on each body segment. On the back is a double row of five pairs of dark blue spots, followed by a double row of six pairs of brick-red spots (fig. 15). Young larvae chew small holes in leaves. Older larvae feed on leaf edges, consuming entire leaves except for the larger veins and the middle rib. Feeding by the large larvae occurs mostly at night. 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.
Larval feeding is completed by mid-June or early July and is followed by pupation, which lasts about 2 weeks. The pupa is dark reddish brown with a sprinkling of reddish hairs. Adults emerge and mate from mid-July through August, Egg laying occurs at this time.
The male moth has a wingspan of about 37 mm (1.4 in) and is dark brown with black bands across the forewings (fig. 16). The female is white with variable black bands across the forewings (fig. 16) 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.
Gallery
 Photo by USDA Forest Service Archive, USDA Forest Service, Bugwood.org | Photo by John H. Ghent, USDA Forest Service, Bugwood.org | Photo by John H. Ghent, USDA Forest Service, Bugwood.org |  Photo by John H. Ghent, USDA Forest Service, Bugwood.org |
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