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European Gypsy Moth - Lymantria dispar L.


Dead trees I

Dead trees II

Dead trees III

Dead trees IV

Larvae I

Larvae II

Larvae III

Pupae: Asian/left, Euro/right

Female laying eggs

Females en masse

Female (top), male (bottom)



European Gypsy Moth
The European gypsy moth has been one of the most destructive exotic forest pests introduced to North America. Gypsy moth larvae feed on the broadest host range of all established exotic pests in North America and prefer hardwood trees. Trees respond to defoliation from larval feeding by producing new leaves at the cost of draining energy reserves. Repeated defoliations will eventually cause decline and tree mortality in some cases. Oak species (Quercus), particularly trees that are stressed or located on dry ridges, are preferred hosts (Gottschalk, 1993). Other overstory and understory species important for timber, habitat, and/or nut production are also subject to attack (Gottschalk, 1993). Gypsy moth damage affects timber and recreational industries and can have a significant impact on wildlife populations and the overall ecosystem (Allen & Bowersox, 1989; Corbett & Lynch, 1987; Swank et al., 1981). Defoliation will cause declines in tree diameter and volume growth (Baker, 1941; Twery, 1987) and the quality of wood can be negatively impacted (Twery, 1990). When populations reach epidemic levels, tree mortality can be as high as 90% (Herrick & Gansner, 1987).

Gypsy moth was deliberately imported in 1869 to the U.S. by Etienne Leopold Trouvelot, an amateur entomologist interested in developing silk production in North America (Liebhold et al., 1995). Trouvelot cultured the larvae on trees in his yard, but some larvae escaped. By 1898 gypsy moth was considered a serious forest pest (Howard, 1898). Over time, the area of permanent infestation has spread west from the northeast into the Lake states and south into Virginia. Spot infestations are in many states and are treated with an eradication strategy. For a highly successful exotic pest, the spread has been relatively slow as the female gypsy moths do not fly. However, dispersal to uninfested locations has been greatly assisted by transportation of egg masses laid upon vehicles, equipment, etc., at infested locations.

Various strategies have been used to combat gypsy moth infestations. These strategies employ insecticides, pathogens (e.g. Bacillus thuringiensis Beliner and Entomophaga maimaiga Humber, Shimazu and Soper, a naturally occurring virus), parasitoids, and silvicultural practices. The strategies selected to address a gypsy moth problem vary with situation and can involve using several tools. States have county-level trapping programs for male moths using pheromone traps to determine presence and population size. In 1991, the USDA Forest Service, in cooperation with APHIS and various states, initiated a pilot program, Slow the Spread, that focused on slowing the spread of gypsy moth by using integrated pest management technology in areas that were in transition from uninfested to permanently infested. The pilot program was such a success that it was expanded in 1999 into a nationwide program (Anonymous, 2003). Through the efforts of this program and other similar efforts, the inevitable march of gypsy moth through North American forests can be slowed until a better solution is developed.

Allen, D. and T. W. Bowersox. 1989. Regeneration in oak stands following gypsy moth defoliations. In Proc. 7th Central Hardwood Conf., G. Rink and C. A. Budelsky, eds., Gen. Tech. Rep. NC-132. United States Department of Agriculture Forest Service, North Central Experiment Station. Pp. 67-73.

Anonymous. 2003. Gypsy moth: Slow the spread program. APHIS PPQ Factsheet -

Baker, W. L. 1941. Effect of gypsy moth defoliation on certain forest trees. J. For. 39: 1017-1022.

Corbett, E. S. and J. A. Lynch. 1987. The gypsy moth - does it affect soil and water resources? In S. Fosbroke and R. R. Hicks Jr. (eds.). Coping with the gypsy moth in the new frontier. W. Va. Univ. Books, Morgantown, WV, pp. 39-46.

Gottschalk, K. W. 1993. Silvicultural guidelines for forest stands threatened by the gypsy moth. United States Department of Agriculture, Forest Service General Technical Report NE-171. 50 pages.

Herrick, O. W. and D. A. Gansner. 1987. Gypsy moth on a new frontier: forest tree defoliation and mortality. Northern J. Appl. For. 4: 128-133.

Howard, L. O. 1898. Danger of importing insect pests. 1898. In Yearbook of the United States Department of Agriculture. 1897. G. M. Hill, Editor. Government Printing Office, Washington. Pp. 529-552.

Liebhold, A. M., W. L. MacDonald, D. Bergdahl, and V. C. Mastro. 1995. Invasion by exotic forest pests: a threat to forest ecosystems. Forest Sci., Monograph 30. 49 pp.

Swank, W. T., J. B. Waide, D. A. Crossley, Jr., and R. L. Todd. 1981. Insect defoliation inhances nitrate export from forest ecosystems. Oecologia 51: 297-299.

Twery, M. J. 1987. Changes in vertical distribution of xylem production in hardwoods defoliated by gypsy moth. Ph.D. thesis, Yale Univ., New Haven, CT., 96 pp.

Twery, M. J. 1990. Effects of defoliation by gypsy moth. USDA gypsy moth research review, pp. 27-34

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