Spongy moth
- French common name: Spongieuse
- Other common names: Gypsy moth, North American gypsy moth
- Scientific name: Lymantria dispar (Linnaeus)
- Kingdom: Animalia
- Phylum: Arthropoda
- Class: Insecta
- Order: Lepidoptera
- Family: Erebidae
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Partial list of synonyms:
- Porthetria dispar (Linnaeus)
General information and importance
Spongy moth is a Eurasian defoliator of hardwood trees. It was introduced accidently to North America near Boston, United States in 1869. It has since become established throughout the temperate woodlands of eastern United States and Canada. Its accelerated spread and defoliation in the 1950s led to repeated applications of the pesticide DDT in the United States. This resulted in negative environmental effects and a ban on DDT.
Spot infestations of spongy moth appeared in Canada near the United States border between Montreal and Kingston throughout the 1960s and 1970s. These infestations were considered eradicated by pesticides. By the 1980s, large areas of defoliation were recorded in southeastern Ontario and eradication in this part of Canada was no longer considered feasible. However, in western Canada, new infestations detected with regular monitoring are still eradicated so that spongy moth does not become established.
The Canadian Food Inspection Agency refers to this insect as the North American spongy moth despite its European origin and status as an alien invasive species. The name is meant to distinguish the regulatory status of the European subspecies of spongy moth, established in eastern North America, from the Asian subspecies not established in North America. The latter have biological differences as well as origins important to regulatory actions.
Distribution and hosts
The spongy moth is currently (2024) established throughout the Great Lakes St-Lawrence and Acadian forest regions in eastern Canada south of 49o. It is frequently detected in pheromone traps in western provinces but has not become established there. This is either a result of eradication programs or natural causes. In the United States, spongy moth is resident throughout the eastern forests from Maine to Virginia and states bordering the Great Lakes.
The primary hosts of spongy moth in both its native and North American ranges are oaks (Quercus). However, most other common hardwood trees in Canada including birch (Betula), poplar (Populus), alder (Alnus), willow (Salix), cherry (Prunus), and apple (Malus), are also susceptible. During outbreaks, spongy moth can be found feeding on a broad list of trees, shrubs, and even ornamental coniferous trees, such as Colorado blue spruce (Picea pungens).
Tree parts affected
Foliage of broadleaf and conifer species
Symptoms and signs
Egg masses are oval-shaped and can be 20 millimetres in length. They are covered in tan-coloured hairs deposited by the female moth, giving the egg masses a soft, spongy appearance (hence the common name, spongy moth). Caterpillars hatching in the spring are 2 to 3 millimetres in length with long black hairs. Mature larvae are up to 60 millimetres in length with two distinctive rows of large spots along the back. The spots are arranged in five pairs of blue and six pairs of red from head to rear. Many long hairs cover the body. Pupae are up to 35 millimetres long. Female moths do not fly but have fully developed, white forewings with faint, darker bands and a wingspan ranging from 37 to 62 millimetres. Male moths are tan brown with irregular black wing markings and wingspans of 37 to 50 millimetres. Males have striking, feather-like antennae to detect the female pheromone.
Egg masses are often well hidden throughout the habitat, such as in rock crevices, under outdoor human structures, and in bark crevasses on the tree. Small larvae feed openly on leaves higher in tree canopies. Large larvae are very conspicuous. They are a large, hairy caterpillar and congregate during the day on shady portions of the tree trunk and lower branches. Larvae often leave the tree to pupate in sheltered places well away from the host plant.
Life cycle
The spongy moth has one generation per year. Adult female moths lay all of their eggs in mid to late summer in one or a few masses, some containing more than 1000 eggs. Embryos progress to the larval stage during warm weather but remain dormant in their egg cases for the winter.
Caterpillars hatch in spring. They climb to the tops of trees where they balloon away on silk threads up to several hundred metres. Eventually they settle and begin feeding in the tree crown. As larvae grow larger, they leave the upper tree crown during the day and congregate on branches lower in the tree. The feeding period lasts six to eight weeks. Larvae pupate in sheltered locations, often away from the host trees. When the flightless female moth emerges, she emits a pheromone that attracts males to mate.
When spongy moth invades new areas, outbreaks often develop quickly where hardwoods (especially oaks) are abundant. The intensity and duration of these outbreaks have been highly variable in North America. As the spongy moth occupied larger forest regions in the 1980s, outbreaks became synchronized over hundreds of kilometres. Modelling historic invasion patterns and seasonality requirements of spongy moth demonstrate that changing climate is creating a greater area of suitability for spongy moth in Canada, especially west of the Great Lakes.
Damage
The rapid increase in spongy moth populations can result in complete defoliation of hardwood trees. Fortunately, healthy trees can re-foliate in the same season. Provided defoliation does not occur several years in a row, tree mortality should not be significant. For the few susceptible conifers, such as eastern hemlock (Tsuga canadensis), the consequences of defoliation by spongy moth can be more severe. The long urticating hairs of spongy moth caterpillars can cause allergic reactions in some people.
The direct economic effects of spongy moth damage for Canadian forestry are modest, as hardwood species of commercial importance are not commonly killed by occasional defoliation events. During outbreaks, consecutive years of defoliation result in some crown dieback and tree mortality. In some cases, however, this mortality has had a thinning benefit and contributed positively to greater forest diversity. Significant economic costs may result from quarantines of infested areas as these result in trade barriers requiring monitoring and eradication programs, phytosanitary inspections, and restrictions on movement of some wood and plant products. Significant socio-economic impacts also result from infestation of valuable amenity trees on private property and public parks.
Prevention and management
Pest management strategies for a particular pest vary depending on several factors. These include:
- the population level of the pest (i.e., how numerous the pest is on the affected host[s]);
- the expected damage or other negative consequences of the pest’s activity and population level (either to the host, property, or the environment);
- an understanding of the pest’s life cycle, its various life stages, and the various natural or abiotic agents that affect population levels;
- how many individual host specimens are affected (an individual tree, small groups of trees, plantations, forests);
- the value of the host(s) versus the costs of pest management approaches; and
- consideration of the various silvicultural, mechanical, chemical, biological, and natural control approaches available and their various advantages and disadvantages.
Decisions about pest management strategies require information about each of these factors for informed decision-making. These various factors should then be weighed carefully in terms of costs and benefits before action is taken against any particular pest.
The most effective long-term management practice for spongy moth is limiting further expansion of its range through restricting invasion pathways. Female spongy moths do not fly, so new infestations are often caused by inadvertent human transport of egg masses deposited on human structures, such as vehicles, outdoor furnishings, and recreational equipment. Movement of these structures and other portable commodities including Christmas trees, nursery stock, and firewood from regulated (infested) areas is restricted by the Canadian Food Inspection Agency (Directive: D-98-09) to reduce new introductions.
Unregulated areas in Canada that are at risk to new introductions and climatically suitable for spongy moth are monitored with pheromone traps to detect new infestations. If these infestations persist or enlarge, eradication programs are carried out. In the United States, a Slow-the-Spread program combined quarantines (to reduce long distance transport by people) with aggressive eradication of short distance infestations along a leading edge. This was successful in delaying expansion of spongy moth on several fronts for many years.
Many of the insect parasitoids attacking spongy moth in its native range have been introduced to North America for biological control. Most of these parasitoids are now common in outbreaks in North America but their effect on population dynamics thus far is not clear. A naturally occurring virus and pathogenic fungus were fortuitously introduced to North America and reduced spongy moth populations from their highest densities. The pathogenic fungus, Entomophaga maimaiga, has been especially effective in reducing populations below damaging levels. Small mammalian predators are important at low densities of spongy moth but do not seem to prevent resurgence of populations.
A naturally occurring virus has been formulated and registered for use, but these pathogens are generally present in populations naturally and function most effectively at very high densities of caterpillars. Experiments to broadcast the pheromone or saturate an infested area with baited traps to capture males before they mate have been used when spongy moth populations are low.
Techniques to suppress outbreaks and eradicate incipient populations often employ aerial or ground applications of insecticides. Pheromones and pesticides are defined as pest control products and are regulated in Canada. Pheromones and pesticides registered for use against spongy moth under specific situations may change from year to year. Therefore, please search Health Canada’s Pesticide Product Information Database for currently registered products and product information for use against this insect. The application of any registered product should be based on population size and applied only when necessary and against the approved life stage. It is also recommended to consult a local tree care professional. Pesticides may be toxic to humans, animals, birds, fish, and other beneficial insects. Apply registered products only as necessary and follow all directions and precautions noted on the manufacturer’s label. In some jurisdictions and situations, only a licensed professional can apply pesticides. Consulting relevant local authorities to determine local regulations that are in place is recommended.
Photos
Egg mass of spongy moth covered in tan-coloured hairs and deposited on the bark of red oak.
Thérèse Arcand
A young spongy moth larva that has recently moulted. The cast skin is visible beneath the larva.
Thérèse Arcand
Mature spongy moth larva on a red oak leaf.
Thérèse Arcand
Adult male spongy moth (wingspan: 35-40 millimetres). Note difference in colouration between male and female moths.
Thérèse Arcand
Spongy moth pupa on a red oak leaf. The cast skin from the last moult is attached to the pupa.
Thérèse Arcand
Spongy moth pupa on a gray birch leaf. The cast skin from the last moult is attached to the pupa.
Thérèse Arcand
Mature spongy moth larva (length: 40-65 millimetres).
Thérèse Arcand
Spongy moth pupa on a red oak leaf. The cast skin from the last moult is attached to the pupa.
Thérèse Arcand
Spongy moth prepupa stage attached to a red oak leaf.
Thérèse Arcand
A female spongy moth laying eggs on the trunk of white birch.
Thérèse Arcand
Adult female spongy moth (wingspan: up to 65 millimetres). Note difference in colouration between male and female moths.
Thérèse Arcand
Spongy moth pupa on the bark of red oak.
Thérèse Arcand
A close-up image of a single spongy moth egg.
Thérèse Arcand
Multiple spongy moth egg masses on a tree trunk.
Pierre Therrien
Stand of gray birch severely defoliated by spongy moth.
Claude Monnier
A close-up image of spongy moth eggs covered in hairs within the egg mass.
Thérèse Arcand
A young spongy moth larva on a sugar maple leaf.
Thérèse Arcand
A pinned adult male spongy moth with wings spread.
Thérèse Arcand
A pinned adult female spongy moth with wings spread.
Thérèse Arcand
A close-up of newly hatched spongy moth larvae showing their numerous hairs and with the tan-coloured egg mass visible beneath many of them.
Thérèse Arcand
Head of a mature larva of spongy moth showing colouration and tufts of hairs characteristic of this species.
Thérèse Arcand
Mature spongy moth larva on trembling aspen.
Thérèse Arcand
A forest of red oak and sugar maple near La Trappe, Quebec, with oak trees preferentially defoliated by spongy moth.
Luc Jobin
Multiple spongy moth egg masses on a white pine trunk.
Luc Jobin
A pheromone trap used to capture of adult males of spongy moth.
Luc Jobin
Gray birch and white pine defoliated by spongy moth.
Claude Monnier
Groups of spongy moth larvae congregating on the trunk and underside of branches on trembling aspen.
Jean-Pierre Bérubé
Selected references
Benoit, P.; Lachance, D. 1990. Gypsy moth in Canada: behaviour and control. Forestry Canada, Headquarters, Corporate and Public Affairs. Ottawa. Information Report DPC-X-32. 22 p. https://ostrnrcan-dostrncan.canada.ca/entities/publication/c01dc141-696e-457d-af36-d99497177129?fromSearchPage=true
Cunningham, J.C.; Brown, K.W.; Scarr, T.A.; Fleming, R.A.; Burns, T. 1996. Aerial spray trials with nuclear polyhedrosis virus and Bacillus thuringiensis on gypsy moth (Lepidoptera: Lymantriidae) in 1994. II. Impact one year after application. Proceedings of the Entomological Society of Ontario 127: 37–43.
Lechowicz, M.J.; Jobin, L. 1983. Estimating the susceptibility of tree species to attack by the gypsy moth, Lymantria dispar. Ecological Entomology 8(2): 171–183. https://doi.org/10.1111/j.1365-2311.1983.tb00496.x
Nealis, V.G. 2009. Still invasive after all these years: keeping gypsy moth out of British Columbia. The Forestry Chronicle 85(4): 593–603. https://doi.org/10.5558/tfc85593-4
Nealis, V.G.; Roden, P.M.; Ortiz, D.A. 1999. Natural mortality of the gypsy moth along a gradient of infestation. The Canadian Entomologist 131(4): 507–519. https://doi.org/10.4039/Ent131507-4
Picq, S.; Wu, Y.; Martemyanov, V.V.; Pouliot, E.; Pfister, S.E.; Hamelin, R.; Cusson, M. 2023. Range-wide population genomics of the spongy moth, Lymantria dispar (Erebidae): Implications for biosurveillance, subspecies classification and phylogeography of a destructive moth. Evolutionary Applications 16(3): 638–656. https://doi.org/10.1111/eva.13522
Pimentel, D.; Lach, L.; Zuniga, R.; Morrison, D. 2000. Environmental and economic costs of nonindigenous species in the United States. Bioscience 50(1): 53–65. https://doi.org/10.1641/0006-3568(2000)050[0053:EAECON]2.3.CO;2
Pogue, M.G.; Schaefer, P.W., 2007. A review of selected species of Lymantria Hübner [1819] including three new species (Lepidoptera: Noctuidae: Lymantriinae) from subtropical and temperate regions of Asia, some potentially invasive to North America. United States Department of Agriculture, Forest Service, Forest Health Technology Enterprise Team. Morgantown, West Virginia. 232 p.
Régnière, J.; Nealis, V.G. 2002. Modelling seasonality of gypsy moth, Lymantria dispar (Lepidoptera: Lymantriidae), to evaluate probability of its persistence in novel environments. The Canadian Entomologist 134(6): 805–824. https://doi.org/10.4039/Ent134805-6
Régnière, J.; Nealis, V.; Porter, K. 2009. Climate suitability and management of gypsy moth invasion into Canada. Pages 135–148 in D.W. Langor, J. Sweeney, editors. Ecological impacts of non-native invertebrates and fungi on terrestrial ecosystems. Springer, Dordrecht. https://doi.org/10.1007/978-1-4020-9680-8_10
Sun, B.; Bogdanski, B.E.C.; Van Hezewijk, B. 2019. The economic feasibility of the gypsy moth eradication program in British Columbia. Natural Resources Canada, Canadian Forest Service, Pacific Forestry Centre. Victoria, British Columbia. Information Report BC-X-450. BC. 25 p. https://ostrnrcan-dostrncan.canada.ca/entities/publication/99d971d6-c486-4787-a7ec-8dde70920d4a?fromSearchPage=true
van Frankenhuyzen, K.; Villedieu, Y. 2004. Epizootic occurrence of Entomophaga maimaiga at the leading edge of an expanding population of the gypsy moth (Lepidoptera: Lymantriidae) in north-central Ontario. The Canadian Entomologist 136(6): 875–878. https://doi.org/10.4039/n04-002