Moths (the adult stage of winter moth) emerge from pupae in the soil usually in mid-late November (usually before Thanksgiving) and may be active into January, whenever the air temperatures are mild (typically when above freezing). The small (0.79-0.98 inch wingspan) male moths are light brown to tan in color and all four wings are edged with small elongate scales that give the hind margins a slightly hairy or fringed appearance. The male moths are strongly attracted to lights and can often be found flying around outdoor lamps or holiday lights. The female (0.31 inch) is gray, almost wingless (brachypterous) and, therefore, cannot fly. She emits a sex pheromone that often attracts clouds of male moths. Females are usually found at the base of trees or scurrying up tree trunks, but can be found almost anywhere.
After mating, the female deposits loose eggs on bark, in bark crevices, under bark scales, on lichen, etc. Each winter moth female may produce 150-350 tiny eggs, which are very difficult to see. The adult moths then die and the eggs over-winter. Eggs are green at first, but turn red-orange soon thereafter. In March, prior to hatching, the eggs turn a bright blue and then a very dark blue-black just before hatching. Eggs hatch when temperatures average around 55º F. It is believed that egg hatch in Massachusetts occurs when 20–50 Growing Degree Days (base 50º F) have accumulated, which can be anywhere from late March into early-mid April, depending on the year and the location. (The Elkinton lab at UMass, uses a base 40º F when completing Growing Degree Day calculations for this insect and suggests that hatch occurs between 177 and 243 GDD (base 40°F, January 1 start date, double sine method).
In most years, egg hatch occurs just at, or right before, bud break of most of the host plants and delayed bud opening due to cool weather can lead to caterpillar death. The newly hatched caterpillars crawl up tree trunks and wriggle between bud scales of newly swelling buds of such hosts as: maple, oak, ash, apple, crabapple, blueberry, and cherry, etc. and begin feeding. Winter moth caterpillars cannot chew their way through closed bud scales, but as the bud scales open, the caterpillars can scrape away at the soft leaf tissue below, producing bullet-hole like damage to the leaf, even before it fully expands. The young larvae also produce strands of silk, which make them air buoyant and this larval dispersal method is known as "ballooning" (like bungee jumping, but not staying tethered to the point of origin). In certain situations, given topography and wind patterns, ballooning winter moth caterpillars can arrive in areas where they have not been expected to be a problem. The caterpillars feed in both flower and foliar buds and, once a bud has been devoured from within, the caterpillar will migrate to other buds and repeat the process. At maturity, the caterpillars will be approximately one-inch-long, whereupon they drop to the soil for pupation. Pupation occurs in late May/early June depending on the geographic location. Areas including Cape Cod are often a week or two behind inland locations.
Winter moth caterpillars are very tiny when newly hatched, less than the size of an eyelash and they are blackish in color at that time. As they feed and increase in size, they are pale green with a faint white longitudinal stripe running down both sides of the body. They are "loopers" or "inchworms" and have just two pairs of prolegs. Winter moth caterpillars are often found in association with both the fall and spring cankerworms, as well as Bruce spanworm (Operophtera bruceata), which are very similar in appearance and have similar feeding patterns to that of the winter moth caterpillar. Fall cankerworm caterpillars have “2 and ½” pairs of prolegs: two pairs of the prolegs are longer than the third, much shorter pair which is counted as number 3 when starting your count from the rear end of the caterpillar. Bruce spanworm is native to the Northeast and is rarely a problem.
Common host plants are apple, blueberry, maple, crabapple, birch and many other deciduous hosts. Larvae hatch in early spring as the host plant buds are swelling and they wriggle into these buds where their feeding can destroy both leaf and flower buds. Destruction of the flower buds leads to greatly diminished harvest on fruit crops such as apple and blueberry. After buds open, the small caterpillars can be found within the tight clusters of new leaves and flowers during the day. During cool springs, if weather hinders leaf expansion but bud scales have begun opening, the winter moth caterpillar can cause high levels of foliar injury as they are protected from insecticides while inside the buds. Winter moth caterpillars often leave foliar clusters to become free feeders at night. Older larvae feed in expanding leaf clusters and are capable of defoliating trees and other plants, when abundant.
Trees bands have been found to be useful for monitoring winter moth egg hatch in the spring. In late October, place a band around the trunk of an oak, maple, or apple tree that has a history of winter moth damage. (Place, or wedge, cotton or polyester fiberfill under the band to prevent the small female moths from going under the band and continuing their climb up the tree.) During peak winter moth population years, individual sticky bands may fill up with adult moths within an hour. In some cases, it has been witnessed that female winter moths, upon approaching the barrier bands, often lay their eggs on the tree trunks just below the barrier and/or crawl over or under the barrier and lay their eggs just above. The eggs are often laid in a circle above and below the band and can be seen with a hand lens.
To monitor for winter moth egg hatch in late-March to early to mid-April, go out and look around the bark directly above or below the bands to check if the eggs have changed color, or are about to hatch, using a hand lens or other magnification. Eggs that are still orange-red are not yet ready to hatch, whereas those that are turning blue are very close to hatching. The observation of the timing of egg hatch may aid in the planning of chemical management options, particularly in crops such as blueberry and apple, where the insecticides must be applied prior to winter moth caterpillars wriggling their way into flower buds to feed.
Tree banding for monitoring may be most useful in production agriculture, such as for apple and blueberry growers in eastern and coastal Massachusetts. For ornamental trees and shrubs, visual monitoring of susceptible hosts in the spring, once leaves have completely opened, can help with determining next steps for management of this insect. Look for tattered leaves or defoliated trees and search for the green caterpillars with 2 pairs of prolegs.
Some products are available and are advertised that the bands act as a barrier to climbing caterpillars, and/or for the climbing adult female moths in late fall to early winter. This method is known as "tree banding". The products for tree banding are generally heavyweight paper or plastic strips that are covered with a sticky substance that snare climbing caterpillars or female moths. However, field observations do not necessarily support the effectiveness of tree bands for reducing winter moth populations when in high numbers and they are therefore not recommended for that purpose. Their main use is in monitoring spring winter moth egg hatch, such as described above in the monitoring section.
Winter moth has been separately introduced into parts of Canada, as well as New England. In Canada, two European parasitoids, Cyzenis albicans, a tachinid fly, and Agrypon flaveolatum, a parasitic wasp were used to reduce winter moth populations below damaging levels. Only the tachinid fly, Cyzenis albicans, has been released in Massachusetts and New England, as it was determined by researchers to be a specialist parasitoid of only the winter moth; on the other hand, A. flaveolatum (the parasitoid wasp) was found to be a generalist that attacked many other species of butterflies and moths. As a result, the parasitoid wasp was not released in Massachusetts.
Research in Canada suggested that once C. albicans brings the densities of winter moth down to a lower level, other sources of mortality, particularly predators (small mammals such as shrews, rove beetles, carabid beetles, and a native wasp) that attack winter moth pupae in the soil over the summer months play a critical role in helping maintain these lower densities. Research led by Dr. Hannah Broadley in Dr. Joseph Elkinton’s lab at the University of Massachusetts, Amherst documented the impact of these predators in the eastern part of the state. Since Cyzenis albicans was released in eastern Massachusetts, the Elkinton lab has documented a decline in the winter moth population, and has declared this a biological control success story. Winter moth has been reduced below outbreak levels in much of eastern Massachusetts.
Abamectin (NL)
Acephate (NL)
Acetamiprid (L)
Azadirachtin (NL)
Bacillus thuringiensis subsp aizawai (larvae) (L)
Bacillus thuringiensis subsp kurstaki (NL)
Bifenthrin (NL)
Chlorantraniliprole (larvae) (NL)
Chlorpyrifos (N)
Chromobacterium subtsugae (NL)
Cyantraniliprole (NL)
Cyfluthrin (larvae) (NL)
Deltamethrin (larvae) (L)
Emamectin benzoate (L)
Flonicamid+cyclaniliprole (N)
Gamma-cyhalothrin (larvae) (L)
Horticultural oil (larvae) (L)
Indoxacarb (L)
Insecticidal soap (NL)
Isaria (paecilomyces) fumosoroseus (NL)
Lambda-cyhalothrin (larvae) (L)
Malathion (L)
Neem oil (NL)
Pyrethrin+sulfur (NL)
Spinetoram+sulfoxaflor (N)
Spinosad (larvae) (NL)
Tau-fluvalinate (NL)
Tebufenozide (NL)
Winter moth has historically been mainly a problem for landscape trees and shrubs (as well as blueberry and apple production) in eastern and coastal Massachusetts. It typically has not reached outbreak (or damaging) levels in the central and western parts of the state. As such, chemical management of winter moth in central and western MA may not be necessary. Do not treat for this insect unless monitoring on the property indicates that an active population is causing tree defoliation.
Active ingredients that may be applied systemically include: abamectin (injection), acephate (injection), acetamiprid (injection), azadirachtin (injection, soil drench), chlorantraniliprole (soil drench), cyantraniliprole (soil drench, soil injection), emamectin benzoate (injection), and neem oil (soil drench).
Soil application of Isaria (paecilomyces) fumosoroseus is labeled for use against caterpillars.
When used in a nursery setting, chlorpyrifos is for quarantine use only.
Make insecticide applications after bloom to protect pollinators. Applications at times of the day and temperatures when pollinators are less likely to be active can also reduce the risk of impacting their populations.
Note: Beginning July 1, 2022, neonicotinoid insecticides are classified as state restricted use for use on tree and shrub insect pests in Massachusetts. For more information, visit the MA Department of Agricultural Resources Pesticide Program.
