Spongy moth male (pale tan-brown, left) females (off white, center), egg cases (beneath females and above), and pupa (far right, dark brown-black) on a tree in Vermont 2021. Photo credit: Jane Lindholm.
The spongy moth has been one of the most destructive exotic forest pests introduced to North America. Spongy 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). Spongy 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).
There are two different ecological types of spongy moth; in the subspecies found across Europe (dispar) the female adult moths are flightless, whereas in the two commonly encountered subspecies found in eastern Asia (asiatica and japonica), the female adults can fly. All of these subspecies were renamed within the species of “spongy moth” in 2022, after the prior common name (“gypsy moth”) was removed from the approved list of names by the Entomological Societies of America and Canada for being a widely acknowledged ethnic slur.
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. Spongy moth is not known to be a critical threat to any of these 15 most vulnerable species.
Widely established dispar subspecies of spongy moth
French specimens of the dispar subspecies of spongy moth were 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 spongy moth was considered a serious forest pest (Howard, 1898). Over time, the area of permanent infestation has spread across the Eastern USA and Eastern Canada. Various strategies have been used to combat spongy 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 spongy 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).
The Slow the Spread Foundation and USDA APHIS maintain maps of the current range of spongy moth in the Eastern USA. This information changes annually. Please view the links below for the most up to date geographic data.
Flight capable asiatica and japonica subspecies
Two subspecies of spongy moth – Lymantria dispar asiatica Vnukovskij and Lymantria dispar japonica Motschulsky – present in Asia are associated with spread via international trade. Lymantria dispar asiatica is found throughout temperate Asia, including the Russian Federation, the Republic of Korea, Mongolia and the Democratic Peoples Republic of China. Lymantria dispar japonica is found in Japan. (NAPPO RSPM #33) Other less common species of Lymantria are found in limited ranges across eastern Asia and are sometimes grouped with Lymantria dispar subspecies for regulatory purposes (Lymantria umbrosa, Lymantria albescens, Lymantria postalba).
These two subspecies of spongy moths may present an even greater threat than the spongy moth subspecies already established in the Eastern US (L. dispar dispar) because they feed upon an even greater variety of plants – more than 600 species of plants, including alder, ash, beech, birch, chestnut, elm, hornbeam, linden, maple, oak, poplar, sumac, trembling aspen, walnut, willow, fruit trees, and certain conifers, including some cedars, Douglas fir, hemlock, juniper, larch, pine, redwood, spruce and some true firs. (NAPPO RSPM#33). In addition, unlike the subspecies found in the Eastern US, the female spongy moths in subspecies asiatica and japonica have the ability to fly up to 40 kilometers (NAPPO RSPM#33); this attribute would greatly accelerate dispersal and colonization if the moths were to escape.
The insect is attracted to lighting at ports, where the females can lay their eggs on ships at anchor or the containers on them. During periods of heavy infestations, regulatory authorities in Russia have reported hundreds of egg masses on a single vessel. (NAPPO RSPM#33)
Beginning in the early 1990s, spongy moths from Asian ports had reached North America on both western and eastern seaboards several times as egg masses on ships (USDA APHIS & Forest Service, 2000). Each time, emergency control programs succeeded in eradicating the moth. Beginning in 1992, the Canadian Food Inspection Service and USDA Animal and Plant Health Inspection Service required that ships that had visited infested ports in the Russian Federation undergo inspection and other measures to ensure that no spongy moth egg masses are present.
Detections of egg masses on ships and cargo aboard ships which had visited Japan, People’ Republic of China, and Republic of Korea began occurring in 1998. Numbers varied considerably, but reached a high of 23 ships in 2008 (Michael Simon, USDA APHIS, pers. comm. Sept 2009).
In response to the rising numbers of detection, Canada, Mexico and the United States – working together through the North American Plant Protection Organization (NAPPO) –developed a regional standard to protect all of North America. After several rounds of negotiations with officials from China, Japan, and Korea, NAPPO adopted the regional standard (RSPM #33) in August 2009. RSPM#33 provides several options for how the Asian countries could prevent transport of spongy moths to North America aboard ship superstructures or cargo containers leaving their ports:
- Inspection and removal of egg masses by the exporting country;
- Systems Approaches – implementation of a systems approach utilizing surveillance and monitoring of insect populations combined with exclusionary tactics (e.g. tree removal in areas near ports, reduction or altering of port lighting, the use of areas of low pest prevalence, etc.)
- Designation of areas of the country as free of spongy moths – verified by monitoring, etc.
- Other measures acceptable to the NAPPO parties
The three NAPPO countries (Mexico, USA, Canada) in turn may require phytosanitary certificate for ships and inspect ships before they enter a North American port. They may also refuse entry of any ship lacking a phytosanitary certificate. If spongy moths are detected, the ship is required to leave waters of the entire NAPPO region until it has been cleaned. If there are repeated incidents of non-compliance, the NAPPO countries will review the exporting country’s management program.
Full implementation of the standard took effect in 2012. Detections of spongy moths via international shipping pathways now rise and fall largely according to the high and low population cycles in the trade partner countries.
While most of the infested ships are attempting to dock at West Coast ports, some are approaching other regions. In 2013, spongy moth eggs were detected on a ship that had travelled from Japan to Europe, then on to the U.S. east coast. Egg masses were discovered when the ship arrived at Baltimore; additional egg masses were detected during the ship’s transit to Brunswick, Georgia; and again when it reached that port (CBP Press Release September 2013). One detection in the United States was in Oklahoma, again in 2013; authorities believe that insect arrived in military equipment (Berger). All known detections of these subspecies of spongy moth have been monitored and eradicated. Nevertheless, the risk of introduction of this highly damaging pest appears to significant.
Additional Websites:
- National Invasive Species Information Center, Spongy Moth page
- USDA APHIS Spongy Moth page
- USDA APHIS Flighted Spongy Moth Complex
- Interactive Map of Spongy Moth Quarantine Areas
- Cornell University, spongy moth information
Sources
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 –
https://www.datcp.state.wi.us/arm/environment/insects/gypsy-moth/pdf/sts_facts.pdf.
Baker, W. L. 1941. Effect of gypsy moth defoliation on certain forest trees. J. For. 39: 1017-1022.
Berger, P. United States Department of Agriculture. Animal and Plant Health Inspection Service. Presentation to the Continental Dialogue on Non-Native Forest Insects and Diseases, November, 2014.
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.
Department of Homeland Security, Bureau of Customs and Border Protection. 2013. Press Release “CBP and Merchant Ship Crew Intercept 27 Destructive Asian Gypsy Moth Egg Masses on Car Carrier Ship.” (Monday, September 30, 2013)
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.
Harriger, K.C. Deputy Executive Director, Agriculture Operational Oversight, Department of Homeland Security, Bureau of Customs and Border Protection. Presentation to the Continental Dialogue on Non-Native Forest Insects and Diseases, November, 2014.
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.
North American Plant Protection Organization (NAPPO) Regional Standards for Phytosanitary Measures (RSPM) #33. 2009. Guidelines for Regulating the Movement of Ships and Cargoes aboard those Ships from Areas Infested with the Asian Gypsy Moth
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: https://doi.org/10.1016/
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.
United States Department of Agriculture, Animal and Plant Health Inspection Service and Forest Service 2000. Pest Risk Assessment for Importation of Solid Wood Packing Materials into the United States. USDA APHIS and Forest Service. August 2000.