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Native elm bark beetle

Written by V.G. Nealis Revision 2025

Maternal tunnel and larval tunnels on an elm trunk
Maternal tunnel and larval tunnels on an elm trunk Louis-Philippe Daviault

General information and importance

Native elm bark beetle is found throughout most of the range of its principal host, white or American elm (Ulmus americana), from Nova Scotia to central Saskatchewan in Canada and from Maine through North Carolina on the Atlantic coast in the United States west to North Dakota in the north and western Tennessee in the south. It was once considered an innocuous bark beetle. Adults feed on twigs and small branches of live elm, and broods are established in dead and dying trees only. However, the insect’s ability to be a vector for two introduced pathogens (Ophiostoma ulmi and O. novo-ulmi) that cause Dutch elm disease have completely changed the impact of the insect. The more virulent O. novo-ulmi, which was introduced more recently than O. ulmi, has become the dominant pathogen that causes Dutch elm disease in Canada. The spores of the pathogen stick to the adult beetle and are transported from diseased trees and inoculated into healthy trees through the feeding activity of the adults. Infected, dying trees then are selected by additional adult bark beetles for their brood, and the next generation of adults become contaminated vectors as well. Either pathogen causes wilting of foliage by clogging the vascular bundles of trees, impeding the ability of the tree to conduct water and nutrients. It is the pathogen and not the beetle that causes death of the tree.

Native elm bark beetle is one of three bark beetles that are a vector for either pathogen causing Dutch elm disease in North America. The other two species are the introduced European elm bark beetle (Scolytus multistriatus) and the introduced banded elm bark beetle (S. schevyrewi). Native elm bark beetle remains the most common vector in Canada because it is more cold-tolerant than the European elm bark beetle; however, it has been displaced by the introduced species in other parts of its range. Both introduced elm bark beetles are the only vectors of Dutch elm disease west of the prairie region.

Distribution and hosts

The insect can be found throughout the range of white or American elm in eastern and central North America: in Canada, from Nova Scotia through the Great Lakes-St Lawrence forests of Quebec and Ontario to central Manitoba and Saskatchewan south of the boreal forest, and in the United States, from Maine through North Carolina on the Atlantic coast to as far west as North Dakota in the north and to western Tennessee in the south.

White or American elm is the primary host. Rock elm (U. thomasii) and slippery or red elm (U. rubra) are less common hosts, especially in Canada. The introduced Siberian elm (U. pumila) and English elm (U. procera) are susceptible to attack by the beetle and there are occasional records of beetle attacks on basswood (Tilia americana) and ash (Fraxinus).

Tree parts affected

Adults of native elm bark beetle feed inconspicuously in the crotches of small twigs of healthy elm trees. This is the common site of pathogen infection. Adults bore into the bark on the lower portions of moribund trees and lay their eggs in galleries in the inner bark. Hatching larvae tunnel through the phloem.

Symptoms and signs

Adult native elm bark beetles are 2.3 to 3.5 millimetres in length, brown, and covered in short, yellowish-red hairs. Their feeding damage on small twigs in the canopies of healthy trees is inconspicuous. Red sawdust on the bark surface around holes in the lower portion of the trunks of moribund trees is evidence of colonization. Peeling away the bark reveals egg galleries with two branches 5 to 7 centimetres long, and only slightly etching the wood. The egg galleries are distinctive among bark beetles in being horizontal or V-shaped across the grain of wood. Feeding tunnels of native elm bark beetle larvae are at right angles to the egg galleries, parallel to the grain of wood. Other elm bark beetles mine egg galleries along the grain of the wood and larvae tunnel across the grain. Larvae (of native elm bark beetles) are creamy white and curved with yellow-brown heads. Mature larvae are 3.5 to 4.0 millimetres in length. Pupation occurs in chambers at the ends of the feeding tunnels just under the bark.

Discoloured, wilted leaves and dead branches seen on previously healthy elm trees are not symptoms of direct attack by native elm bark beetle but of Dutch elm disease.

Life cycle

Native elm bark beetles usually have one generation per year in Canada. A partial or full second generation has been recorded in southern parts of the range. Beetles overwinter as adults in bark crevices or shallow tunnels at the base of healthy elm trees or as larvae within their feeding tunnels. Where there is a partial second generation, their brood also overwinter as larvae resulting in two distinct periods of adult activity in spring and in late summer the following year.

Adults emerging in spring feed on twigs and small branches in the crowns of healthy elms. If spores of the pathogen are stuck to the beetle cuticle, trees will become infected via the feeding scars. Mature adults then locate dead or dying trees by volatile attractants produced by the host. The adult females bore into the lower bole of the tree to establish broods. Egg galleries of the native elm bark beetle are constructed across the grain of the wood. Pupal chambers resulting from broods initiated in the early part of the season (May and June) are formed at the ends of the feeding tunnels. Adults emerge in late summer and are attracted to healthy trees, where they feed and eventually choose hibernation sites low on the tree trunk. A small proportion of these new adults will initiate a second generation, but most later broods are produced by the beetles that had overwintered as larvae and emerged as adults in late summer. The broods of these late-summer adults also overwinter as larvae.

Damage

Native elm bark beetle causes little direct damage to healthy elm trees. It is their role as vectors of either pathogen causing Dutch elm disease that has changed the ecological relationship between the beetle and forest health. Dutch elm disease has caused catastrophic mortality to elm, which was once a dominant hardwood tree of eastern North America and favoured amenity tree in urban settings.

Prevention and management

The dramatic impact of Dutch elm disease has resulted in many chemical control programs aimed at suppressing populations of the native elm bark beetle. The habit of the adult beetle to enter the base of healthy trees to overwinter creates the opportunity to apply insecticides in a restricted area where adults are likely to be exposed.

Sanitation and prevention are the main management tools, particularly in early May when new broods are being initiated. When infested or injured trees are felled, they should not be left in vicinity of healthy trees. All bark from felled material as well as the stump should be removed and buried. Regular monitoring of elm bark beetle vectors, disease symptoms, and rapid removal and destruction of infected trees are key components of management. Pruning diseased branches is common, although more likely to retard rather than stop progress of the disease. Pruning scars may attract adult elm bark beetles unless the wound is dressed. Restrictions on movement of firewood or any wood with bark out of infected areas is important because this is a common pathway of transferring both beetles and the disease.

Infected elm trees in amenity situations can be replaced with non-susceptible species. There appears to be a genetic basis to vulnerability, so collecting seed from young elms that are apparently resistant to Dutch elm disease would be a step toward establishing resistant stock.

Pest management strategies for a particular pest vary depending on several factors. These include:

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.

Pesticides registered for use against native elm bark beetle 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. Chemical pesticides may be toxic to humans, animals, birds, fish, and other beneficial insects. Apply registered products only as necessary and according to 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

Adult in its v-shaped tunnel

Adult in its v-shaped tunnel

Thérèse Arcand

Side view of the adult (length: 2.5 mm)

Side view of the adult (length: 2.5 mm)

Thérèse Arcand

Maternal tunnel and larval tunnels on an elm trunk

Maternal tunnel and larval tunnels on an elm trunk

Louis-Philippe Daviault

Selected references

Anderson, P.L.; Holliday, N.J. 2003. Distribution and survival of overwintering adults of the Dutch elm disease vector, Hylurgopinus rufipes (Coleoptera: Scolytidae), in American elm trees in Manitoba. Agricultural and Forest Entomology 5(2): 137–144. https://doi.org/10.1046/j.1461-9563.2003.00178.x

Aoun, M.; Rioux, D.; Simard, M.; Bernier, L. 2009. Fungal colonization and host defense reactions in Ulmus americana callus cultures inoculated with Ophiostoma novo-ulmi. Phytopathology 99(6): 642–650. https://doi.org/10.1094/PHYTO-99-6-0642

Blanchette, R.A. 2023. Dutch elm disease–symptoms and elm bark beetles. Diseases of forest and shade trees. College of Food, Agriculture and Natural Resources. University of Minnesota. https://treediseases.cfans.umn.edu/dutchelm1[Accessed March 2023]

Finnegan, R.J. 1957. Elm bark beetles in southwestern Ontario. The Canadian Entomologist 89(6): 275–280. https://doi.org/10.4039/Ent89275-6

Gardiner, L.M. 1981. Seasonal activity of the native elm bark beetle, Hylurgopinus rufipes, in central Ontario (Coleoptera: Scolytidae). The Canadian Entomologist 113(4): 341–348. https://doi.org/10.4039/Ent113341-4

Magasi, L.P.; Urguart, D.A.; Harrison, K.J.; Murray, D.M. 1993. Three decades of Dutch elm disease in Fredericton, N.B. Natural Resources Canada, Canadian Forest Service, Atlantic Forestry Centre. Fredericton, New Brunswick. Information Report M-X-185E. 39 p.

Martín, J.A.; Domínguez, J.; Solla, A.; Brasier, C.M.; Webber, J.F.; Santini, A.; Martinez-Arias, C.; Bernier, L.; Gil, L. 2023. Complexities underlying the breeding and deployment of Dutch elm disease resistant elms. New Forests 54: 661–696. https://doi.org/10.1007/s11056-021-09865-y

Swedenborg, P.D.; Jones, R.L.; Ascerno, M.E.; Landwehr, V.R. 1988. Hylurgopinus rufipes (Eichhoff) (Coleoptera: Scolytidae): attraction to broodwood, host colonization behavior, and seasonal activity in central Minnesota. The Canadian Entomologist 120(12):1041–1050. https://doi.org/10.4039/Ent1201041-12

Takai, S.; Kondo, E.S.; Thomas, J.B. 1979. Seasonal development of Dutch elm disease on white elms in central Ontario, Canada. II. Following feeding by the North American native elm bark beetle. Canadian Journal of Botany 57(4): 353–359. https://doi.org/10.1139/b79-047

Cite this fact sheet

Nealis, V.G. 2025. Native elm bark beetle. 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.