European Gypsy Moth

european gypsy moth
Lymantria dispar L.
Last updated by:

Faith Campbell

The European gypsy moth has been one of the most destructive exotic forest pests introduced to North America. Gypsy moth larvae feed on 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. 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. Since 1991, the USDA Forest Service, USDA Animal and Plant Health Inspection Service (APHIS) and various states have operated a Slow-the-Spread program.  The STS program has succeeded in slowing the insect’s spread by using integrated pest management technology in areas that were in transition from uninfested to permanently infested (Anonymous, 2003).

USFS scientists and managers developed a conservation priority-setting framework for forest tree species at risk from pest & pathogens and other threats. The Project CAPTURE (Conservation Assessment and Prioritization of Forest Trees Under Risk of Extirpation) uses FIA data and expert opinion to group tree species under threat by non-native pests into vulnerability classes and specify appropriate management and conservation strategies. The scientists prioritized 419 tree species native to the North American continent. The analysis identified 15 taxonomic groups requiring the most immediate conservation intervention because of the tree species’ exposure to an extrinsic threat, their sensitivity to the threat, and their ability to adapt to it. Each of these 15 most vulnerable species, and several additional species, should be the focus of both a comprehensive gene conservation program and a genetic resistance screening and development effort.  European Gypsy Moth is not known to be a threat to any of these 15 most vulnerable species. 

In the decade since 2005, only 38 new counties have gypsy moth populations; all border counties infested by 2005.  Sixteen of these counties are in the Appalachian mountains of Virginia and West Virginia; ten additional counties are in Wisconsin  (see APHIS quarantine map ). 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.

As of 2014, gypsy moth populations in the infested area of the Northeast have remained low compared to previous decades.  In 2015, notable defoliation occurred in Pennsylvania, New Jersey, and West Virginia (Rabaglia pers. comm.)

Additional Websites:


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.

Potter, K.M., Escanferla, M.E., Jetton, R.M., Man, G., Crane, B.S., Prioritizing the conservation needs of US tree spp: Evaluating vulnerability to forest insect and disease threats, Global Ecology and Conservation (2019), doi:

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.