Winter moth
- French common name: Arpenteuse tardive
- Other common names: Common winter moth, European winter moth
- Scientific name: Operophtera brumata (L.)
- Kingdom: Animalia
- Phylum: Arthropoda
- Class: Insecta
- Order: Lepidoptera
- Family: Geometridae
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Partial list of synonyms:
- Cheimatobia brumaria (Esper)
- Cheimatobia vulgaris (Stephens)
- Cheimatobia. myricaria (Cooke)
- Phalaena. grisearia (Villers)
- Thysanodes phryganea (Rambur)
General information and importance
Winter moth is native to Europe and most of Eurasia, including Japan. It was introduced accidentally to Nova Scotia in the 1930s but mistaken for the closely related, but native, Bruce spanworm. The same error occurred in British Columbia where winter moth was not recognized as an alien invasive species until 1976 despite causing damage for several years previously. Genetic analyses indicate the introductions to eastern and western North America were independent and from different sources in Europe. Genetic studies also confirm winter moth and native Operophtera species in the Bruce spanworm complex are hybridizing in North America.
Original observations of winter moth were made in southwestern Nova Scotia in the late 1940s. By 1970, populations were established throughout Nova Scotia, Prince Edward Island, and southern New Brunswick. Subsequent surveys show winter moth has not extended its range into cooler regions northward in Atlantic Canada for the past 50 years. Severe outbreaks, which were observed during the early years of range expansion, have become less frequent. The invasion history of British Columbia suggests similar climatic limits because winter moth has established only on southern Vancouver Island and on the Lower Mainland near the coast. However, unlike winter moth populations in Atlantic Canada, populations on southern Vancouver Island remain chronically high.
Winter moth gets its common name as one of the few moths visibly active in late autumn and early winter in northern environments. It is the male moths that are seen flying on cold nights in search of the flightless females.
Distribution and hosts
Winter moth is one of the most widely distributed forest insects in the northern hemisphere owing, in part, to its broad host range. European range expansion northward into Fennoscandia because of warmer winters has occurred in recent years, as has a further expansion in the list of host plants utilized by winter moth.
The current distribution of winter moth in North America is restricted to the moderate temperate climates of south Vancouver Island and adjacent mainland in western Canada, the Maritime coast of eastern Canada, and the adjacent northeastern Atlantic states of the United States (Plant Hardiness Zones 5b and warmer). Based on climate matching, winter moth could survive in temperate southern Ontario, Quebec, and southern British Columbia if it dispersed there naturally or was introduced accidentally. Moderating conditions associated with climate change increase the risk of further expansion of winter moth in North America.
Winter moth feeds on many species of deciduous trees and shrubs and some conifers. Throughout its native and introduced ranges, oak (Quercus), maple (Acer), birch (Betula), and elm (Ulmus) are the most common hosts. It can also be a pest of apple (Malus), pear (Pyrus), cherry (Prunus), and blueberry (Vaccinium).
Tree parts affected
Symptoms and signs
Eggs are 0.70 millimetres long. They are pale green at first but turn orange within a few days if fertilized. Larvae are green with a dark green mid-dorsal stripe and three pale yellow lateral stripes. These markings disappear just before pupation. The female winter moth is 10 millimetres long with vestigial wings. Male moths are light tan in colour with a maximum wingspan of 30 millimetres, including a fringe of scales on the outer margins of the wings. Adult moths are the most conspicuous life stage as they fly at night from late autumn to early winter and are attracted to lights.
Much of the damage occurs early in the season when larvae are feeding within buds. It becomes evident as leaves unfold to reveal a characteristic pattern of holes in the expanding leaf. Larvae may be seen hanging on silk threads beneath trees throughout the feeding period. Fully grown larvae are about 18 millimetres long.
Life cycle
Eggs are laid singly (but usually clustered relatively close together) in protected bark crevices or on lichen or moss near the lower trunk of trees from November to early January. Eggs hatch as early as March in British Columbia and as late as mid-May in eastern Canada. The degree of synchrony between egg hatch and development of early season buds is an important determinant of local survival rates. Synchrony between egg hatch in the spring and local development of tree buds may affect apparent preference among available hosts in any given location or year.
As newly hatched larvae forage for early buds, they drop on silk threads and are dispersed several hundred metres by ballooning on air currents. Adult females do not fly, so the dispersal of small larvae has been the primary mechanism of spread. Survey records show gradual spread from the original point of introduction in southwestern Nova Scotia toward the northeast in the direction of prevailing winds.
Larvae enter developing buds and complete their feeding from late May to early June in British Columbia, and later in Atlantic Canada. As the larvae and the leaves on which they feed develop, they fold the leaf into a loose shelter. When the feeding period is complete, the larvae descend to the ground on silk threads and pupate in underground cells where they remain for the rest of the summer. Adult moths emerge from late autumn to early winter. The wingless female winter moth manages to climb a short distance up a tree and emits a mating pheromone to attract males. After mating, the female climbs further up the tree, laying eggs in protected bark crevices.
Damage
Despite the relatively small size of winter moth larvae, their early emergence and feeding habit inside small, developing buds can cause significant damage to new plant growth. Relatively high levels of tree mortality occurred from severe defoliation following the initial introduction to Nova Scotia. However, since populations collapsed in the mid-1960s, significant damage in eastern Canada has been restricted to sparsely distributed trees and shrubs, as well as amenity and fruit trees. Damage has also diminished in coastal British Columbia since initial outbreaks, but visible damage to Garry oak (Quercus garryana) in the Victoria region continues to occur, as does damage to local fruit trees.
Periodic cyclical behaviour of winter moth populations has been identified in Europe where longer historical records are available. Expansion of geographic and host ranges is also occurring there. In North America, the severe defoliation following initial introductions no longer occurs; therefore, if there are cycles, they are oscillating at low population densities. The collapse in population densities in Canada is correlated to introduction and establishment of natural enemies.
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.
As an alien invasive species, winter moth is regulated by the Canadian Food Inspection Agency with restrictions on moving firewood, which may harbour winter moth eggs (Directive D-01-12).
Winter moth has been the target of biological control since its discovery in North America. Several parasitic insects (parasitoids) have been introduced. One species, the tachinid fly (Cyzenis albicans), has been the most successful in becoming established and spreading naturally, and by purposeful relocation. This parasitoid effectively reduces high-density populations of winter moth. Once populations have declined, local predators feeding on pupae in the soil during the summer inflict sufficient mortality to maintain low population levels of winter moth for several years. The extent to which soil predators maintain populations at these low levels varies as a function of the local abundance and response of these predators.
The protected feeding habit of winter moth within buds makes targeting with pesticides difficult. Fortunately, the limited damage caused by defoliation of forest trees has made intervention rarely necessary. Sticky bands around tree trunks are used to trap or impede female moths in the fall and hatching larvae in the spring, and this is a common option for individual trees. Commercial fruit trees are often treated for related pests, which likely reduces winter moth populations as well. Pesticides registered for use against winter moth under specific situations may change from year to year. Therefore, please search Health Canada’s Pesticide Product Information Database for currently registered pesticides 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
Pupae
Hannes Lemme www.forestryimages.org
Larvae
Milan Zubrick, Forest Research Institute - Slovakia, www.forestryimages.org
Larvae
Fabio Stergulc, University of Udine, www.forestryimages.org
Female imago, climbing up host tree
Hannes Lemme www.forestryimages.org
Female with reduced wings
Daniel Adam, Office National des Forêts - France, www.forestryimages.org
Male
Louis-Michel Nageleisen, Département de la Santé des Forêts - France, www.forestryimages.org
Selected references
Elkinton, J.; Boettner, G.; Liebhold, A.; Gwiazdowski, R. 2014. Biology, spread, and biological control of winter moth in the eastern United States. United States Department of Agriculture, Forest Service. Publication FHTET-2014-07. https://www.fs.usda.gov/nrs/pubs/jrnl/2015/fhtet-2014-07_elkinton_2015_001.pdf [Accessed September 2024]
Embree, D.G. 1965. The population dynamics of the winter moth in Nova Scotia, 1954–1962. Memoirs of the Entomological Society of Canada 97(Supplement S46): 5–57. https://doi.org/10.4039/entm9746fv
Embree, D.G. 1991. The winter moth Operophtera brumata in eastern Canada, 1962-1988. Forest Ecology and Management 39: 47–54. https://doi.org/10.1016/0378-1127(91)90161-N
Gwiazdowski, R.A.; Elkinton, J.S.; DeWaard, J.R.; Sremac, M. 2013. Phylogeographic diversity of the winter moths Operophtera brumata and O. bruceata (Lepidoptera: Geometridae) in Europe and North America. Annals of the Entomological Society of America 106(2): 143–151. https://doi.org/10.1603/AN12033
Nealis, V.G.; DeMerchant, I.; Langor, D.; Noseworthy, M.K.; Pohl, G.; Porter, K.; Shanks, E.; Turnquist, R.; Waring, V. 2016. Historical occurrence of alien arthropods and pathogens on trees in Canada. Canadian Journal of Forest Research 46(2): 172–180. https://doi.org/10.1139/cjfr-2015-0273
Roland, J.; Embree, D.G. 1995. Biological control of the winter moth. Annual Review of Entomology 40: 475–492. https://doi.org/10.1146/annurev.en.40.010195.002355