Eastern blackheaded budworm
- French common name: Tordeuse à tête noire de l'épinette
- Other common names: black-headed budworm, hemlock budworm
- Scientific name: Acleris variana (Fernald)
- Kingdom: Animalia
- Phylum: Arthropoda
- Class: Insecta
- Order: Lepidoptera
- Family: Tortricidae
-
Partial list of synonyms:
- Peronea variana Fernald
General information and importance
Eastern blackheaded budworm is a native defoliator in Canadian spruce-fir forests, east of the Rocky Mountains to Newfoundland and Labrador. Until the 1970s, it was considered a single, transcontinental species, which varied in its host preference from balsam fir (Abies balsamea) in the east to western hemlock (Tsuga heterophylla) in the west. The western populations are now considered a separate species, (western blackheaded budworm, Acleris gloverana) although no definitive genomic differences have been demonstrated. The species name variana refers to the highly variable colour patterns of the adult moth.
Although eastern blackheaded budworm is common throughout its range, significant outbreaks in Canada occur in moist maritime forests of the Atlantic provinces, especially where balsam fir is dominant. The first outbreak was recorded in the late 1920s in Nova Scotia. Since then, outbreaks have occurred at about 10- to 15-year intervals. Significant defoliation usually does not last more than 2 years. Outbreaks of eastern blackheaded budworm are often concurrent with outbreaks of spruce budworm (Choristoneura fumiferana), balsam woolly adelgid (Adelges piceae), or hemlock looper (Lambdina fiscellaria). These outbreaks all occur in the same stands, making it difficult to characterize the damage caused solely by eastern blackheaded budworm.
Distribution and hosts
This insect is found throughout Canadian spruce-fir forests, east of the Rocky Mountains and similar forests in the northeastern United States. The primary hosts are balsam fir and white spruce (Picea glauca). Balsam fir is the more common host east of the Great Lakes, and white spruce west of the Great Lakes to the Rocky Mountains. Red spruce (P. rubens), black spruce (P. mariana), larch (Larix), and eastern hemlock (T. canadensis) may also host eastern blackheaded budworm.
Host parts affected
Symptoms and signs
Oval eggs are laid singly on the underside of needles. Female moths attach a tuft of scales from their abdomens on the eggs. Newly hatched larvae are 1 millimetre long and pale green, with dark brown or black heads. Fully-grown larvae are 11 to 15 millimetres long, and uniformly green, similar to the colour of balsam fir needles. The colour of head capsules varies from solid reddish to dark brown and black. Adults are medium-sized moths with wingspans from 7.5 to 9.1 millimetres. As their name indicates, colour patterns can be extremely variable. They range from a simple grey base colour with a light-colour median band to an ochreous base colour with bands and mottled markings.
Defoliation appears suddenly. The first evidence of damage is a red tinge on the outer portions of branches in the upper crowns of host trees. This is caused by dead needles, which the larvae have detached to construct feeding shelters. These symptoms are more pronounced on balsam fir than on spruce.
Life cycle
Eastern blackheaded budworm has one generation per year. Eggs are laid singly on the underside of needles on branch tips in the upper tree crowns from late summer to early fall. Female moths cover their eggs with a tuft of scales from their abdomens. The insect overwinters in the egg stage. Eggs hatch in May to early June and larvae bore into fresh buds. The availability of suitable foliage is critical for survival in these early stages. As shoots flush, budworms chew needles at the base and web them together with silk to form a compressed feeding shelter. Toward the end of the feeding period, larvae feed more openly. When densities are high, larvae can feed on previous years’ needles, particularly on balsam fir. Pupae are formed in the final feeding shelter in late August and adults emerge throughout September. Female moths emit a sex pheromone to attract males.
Moths are active flyers and may disperse long distances. The dispersal of moths away from damaged stands contributes to the short duration of outbreaks.
Many species of native natural enemies attack eastern blackheaded budworm, including insect parasitoids and generalist predators, such as ants and migratory songbirds. Available data suggest outbreak cycles are the result of the delayed and combined actions of these natural enemies. These actions increase with eastern blackheaded budworm populations but are lagged in time. The greater frequency of outbreaks in Atlantic Canada is thought to be the result of variable weather conditions characteristic of this region.
Damage
Tree mortality is not common unless severe defoliation lasts more than 2 years or is exacerbated by co-occurrence of other defoliators, such as spruce budworm. Unlike western blackheaded budworm, eastern blackheaded budworm does not cause significant damage to juvenile stands. Outbreaks are confined to mature forest stands where there may be some top-kill and a temporary reduction in growth rates.
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.
Sampling methods to monitor populations of eastern blackheaded budworm include sampling to estimate egg densities and pheromones to monitor moths. The brief period of defoliation makes large-scale application of pesticides difficult to target and the low rates of mortality in mature stands usually make such applications unnecessary.
Pesticides and pheromones are defined as pest control products and are regulated in Canada. Products registered for use against eastern blackheaded budworm 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.
Selected references
Berryman, A.A. 1986. On the dynamics of blackheaded budworm populations. The Canadian Entomologist 118(8): 775–779. https://doi.org/10.4039/Ent118775-8
Gage S.H.; Miller, C.A.; Mook, L.J. 1970. The feeding response of some forest birds to the black-headed budworm. Canadian Journal of Zoology 48(2): 359–366. https://doi.org/10.1139/z70-057
Miller, C.A. 1966. The black-headed budworm in eastern Canada. The Canadian Entomologist 98(6): 592–613. https://doi.org/10.4039/Ent98592-6
Otvos, I.S.; Fajrajsl, A. 1997. An annotated bibliography of Acleris variana and Acleris gloverana. Natural Resources Canada, Canadian Forest Service, Pacific Forestry Centre. Victoria, British Columbia. Information Report BC-X-371. 81 p.
West, R.J.; Carter, J. 1992. Aerial applications of Bacillus thuringiensis formulations against eastern blackheaded budworm in Newfoundland in 1990. Forestry Canada, Newfoundland and Labrador Region. St. John’s, Newfoundland and Labrador. Information Report N-X-282. 10 p.
Cite this fact sheet
Nealis, V.G. 2024. Eastern blackheaded budworm. In J.P. Brandt, B.I. Daigle, J.-L. St-Germain, A.C. Skinner, B.C. Callan, and V.G. Nealis, editors. Trees, insects, mites, and diseases of Canada’s forests. Natural Resources Canada, Canadian Forest Service, Headquarters. Ottawa, Ontario.Photos
Young larva of eastern blackheaded budworm on balsam fir.
Thérèse Arcand
Young larva of eastern blackheaded budworm on balsam fir.
Thérèse Arcand
Mature larva of eastern blackheaded budworm in its silken feeding shelter on a white spruce shoot. Partially consumed needles will turn reddish brown as they dry.
Thérèse Arcand
Young larva of eastern blackheaded budworm on white spruce.
Thérèse Arcand
Adult moth of eastern blackheaded budworm, pinned with wings spread. Note the variation in colour and pattern of the wings in this photo and photos of other adult moths, either at rest or pinned.
Thérèse Arcand
Adult moth of eastern blackheaded budworm, pinned with wings spread. Note the variation in colour and pattern of the wings in this photo and photos of other adult moths, either at rest or pinned.
Thérèse Arcand
Adult moth of eastern blackheaded budworm, pinned with wings spread. Note the variation in colour and pattern of the wings in this photo and photos of other adult moths, either at rest or pinned.
Thérèse Arcand
Adult moth of eastern blackheaded budworm, pinned with wings spread. Note the variation in colour and pattern of the wings in this photo and photos of other adult moths, either at rest or pinned.
Thérèse Arcand
Pupa of eastern blackheaded budworm tied with silk to several balsam fir needles.
Thérèse Arcand
Pupa of eastern blackheaded budworm removed from its final feeding shelter on a balsam fir needle. Note the abundant frass from the last larval stage in and around the final feeding shelter.
Thérèse Arcand
Adult moth of eastern blackheaded budworm, at rest. Note the variation in colour and pattern of the wings in this photo and photos of other adult moths, either at rest or pinned.
Thérèse Arcand
Adult moth of eastern blackheaded budworm at rest on white spruce. Note the variation in colour and pattern of the wings in this photo and photos of other adult moths, either at rest or pinned.
Thérèse Arcand
Adult moth of eastern blackheaded budworm at rest on white spruce. Note the variation in colour and pattern of the wings in this photo and photos of other adult moths, either at rest or pinned.
Thérèse Arcand
Mature larva of eastern blackheaded budworm on white spruce.
Robert W. Duncan Centre de foresterie du Pacifique, Victoria (Colombie-Britannique) / Pacific Forestry Centre, Victoria, British Columbia