- In North America, "winter moth" usually denotes the invasive species Operophtera brumata, but may also mean a native species, Erannis tiliaria (Linden looper).
The winter moth (Operophtera brumata) is a moth of the family Geometridae. It is an abundant species of Europe and the Near East and one of very few Lepidoptera of temperate regions in which adults are active in late fall and early winter. The female of this species is virtually wingless and cannot fly, but the male is fully winged and flies strongly. After the initial frosts of late fall, the females walk to and up trees, there emitting pheromones in the evening to attract males. Fertilized, she ascends to lay, on average, around 100 eggs.
Winter moths are considered an invasive species in North America. Nova Scotia, Canada, experienced the first confirmed infestations in the 1930s. The moth began to appear in eastern states of the United States in the 1950s, and is now well established in Massachusetts, Rhode Island, New Hampshire and Maine. In the late 1950s winter moths appeared in the Pacific northwest, and are confirmed present in British Columbia, Washington and Oregon. In Massachusetts, the moths have attracted the attention of several media outlets due to the severity of the infestation. Efforts at biological control are underway.
The forewing ground colour of the winged males varies from grey-yellow to beige-brown or occasionally slightly reddish-tinted. The patterns are often band-shaped dark brownish, often indistinct. The fringe is yellowish. The hindwings are pale grey or yellow grey. The antennae are short and finely hairy. The flightless female has a brownish-grey body with rudimentary wing stubs that are brown to grey and have dark bands. Body length for both sexes approximately 1.0 centimeters. Larvae at hatching are 1/10 inch (2.5 mm) in length and will grow to 3/4 inch (20 mm) over a six week period.
Native to Northern and Central Europe: In the South, its range extends to Northern Italy; in the East to the Caucasus and Asia Minor; in the North to the Baltic. As an invasive species, this moth is found in southern New England and also the Pacific northwest. In New England, expansion inland and north appears to be curtailed by cold winter temperatures, so for example, coastal Maine but not inland. Locally milder winters, as part of global climate change, may be allowing expansion of afflicted territory. A study conducted in Massachusetts documented that winter moth defoliation reduced the annual trunk diameter growth rate of oak trees by an average of 47% while not significantly impacting growth rates of the less defoliated maple trees.
Winter moth larvae (caterpillars) emerge in early spring from egg masses laid near leaf buds after a series of days in which the daytime high temperatures reach into the 50s Fahrenheit. Research conducted in the Netherlands indicated that as climate warming is causing spring temperatures to become warmer sooner, some of the winter moth eggs were hatching before tree leaf buds - first food for the caterpillars - had begun to open. Early hatchlings starved. Late hatchlings survived. Because hatch timing is genetically controlled, the moths are evolving to resynchronize with bud opening by delaying the response to the temperature trigger by 5 to 10 days. The larvae, like the adults, can withstand below freezing temperatures at night. Larvae prefer Oak and Apple, but also feed on Maple, Birch, Hornbeam, Chestnut, Hazel, Quince, Beech, Larch, Poplar, Cherry, Pear, Rose, Raspberry, Blueberry, Willow, Elm, and other leafy trees and shrubs.
Recently hatched larvae feed on expanding leaf buds, often after having burrowed inside the bud, and later on foliage, for approximately six weeks. In addition to feeding on the tree where they hatched, young larvae will also product silk strands to 'balloon' (be wind-blown) to other trees. Defoliation can approach 90%. By mid-May the larvae, green in color and about an inch long, descend to the ground. Pupation occurs in the soil in late May. Adults emerge from the soil in late fall to early winter, when, upon mating, the flightless female lays eggs in bark crevices and on branches.
In Europe, where winter moths are native, two parasitic species, a wasp (Agrypon flaveolatum) and a fly (Cyzenis albicans) prey on winter moth caterpillars. The wasps insert eggs into the larvae. The flies lay eggs on leaves, which the larvae ingest when eating the leaves. As a biological control, the wasp avenue was used in Canada but is not being pursued in the United States because there is not sufficient evidence that the wasp would not lay eggs in larvae of other moth species. Introduction of C. albicans, which is species-specific to preying on winter moths, has proven successful in strongly reducing, although not entirely eliminating, winter moth infestation in Nova Scotia, Canada. Test introductions were begun in eastern Massachusetts in 2005. This proved successful, so more fly releases have taken place at sites from southeast Connecticut to coastal Maine. As moth densities can reach ten million larvae per acre, several years are needed before parasitism by the flies reaches 20-50%. Once this is achieved the winter moth density declines and leaf defoliation is reduced to levels not as harmful to the trees. Researchers have found however, that the mortality caused by the fly is not density-dependent; the most important cause of mortality of the larvae of the winter moth is a lack of synchrony between the eggs hatching and the availability of new foliage as leaf and flower buds begin to hydrate and grow, referred to as bud break and bud burst.
- Cairn, North (8 December 2012). "Experts: Destructive winter moths are spreading". Portland Press Herald. Portland, Maine. Retrieved 9 December 2012.
- Noonan, Erica (3 December 2009). "Mystery Pests". Boston Globe. Boston, Massachusetts. Retrieved 9 December 2012.
- Winter Moth in Massachusetts: History and Biological Control University of Massachusetts Extension, The Center for Agriculture, Food and the Environment (2017). Accessed Dec 6, 2017.
- Winter Moth Identification & Management UMass Extension The Center for Agriculture, Food and the Environment (2017) Accessed December 7, 2017.
- The Relationship Between the Winter Moth (Operophtera brumata) and Its Host Plants O'Donnell KM. University of Maine (2015)
- Winter Moth Proves Able To Adjust To Climate Change. Netherlands Institute of Ecology (2007).
- Simmons MJ, Lee TD, Ducey MJ, Elkinton JS, Boettner GH, Dodds KJ (2014). "Effects of Invasive Winter Moth Defoliation on Tree Radial Growth in Eastern Massachusetts, USA". Insects. 5 (2): 301–18. doi:10.3390/insects5020301. PMC . PMID 26462685.
- Capinera, John L. (2008). Encyclopedia of Entomology. Springer Science & Business Media. p. 4278. ISBN 978-1-4020-6242-1.
- Huffaker, C. (2013). Biological Control. Springer Science & Business Media. p. 103. ISBN 978-1-4615-6528-4.
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