Brown spruce longhorn beetle

Written by J.P. Brandt Revision 2024

• French common name: Longicorne brun de l'épinette
• Scientific name: Tetropium fuscum (Fabricius)
• Kingdom: Animalia
• Phylum: Arthropoda
• Class: Insecta
• Order: Coleoptera
• Family: Cerambycidae

General information and importance

Brown spruce longhorn beetle is not native to Canada. It was discovered in 1999 in Point Pleasant Park near Halifax, Nova Scotia and likely arrived in infested wood packaging of goods imported from Europe. Research in Nova Scotia indicates that it prefers to attack and has greatest survival in live mature spruce trees with reduced growth rates and low vigour. It will occasionally attack healthy trees, but its rate of development and survival is greatly reduced unless the tree becomes stressed by other factors (e.g., wind damage).

Distribution and hosts

In North America, this insect is known to be present only in Nova Scotia and an isolated location near Calhoun, New Brunswick, Canada. It occurs primarily on red spruce (Picea rubens) but also on white (P. glauca), black (P. mariana), and Norway spruce (P. abies). The insect’s native range is discontinuous. It is found in Europe from Scandinavia to Turkey, Japan, and western Siberia. The primary host in its native range is Norway spruce, with rare reports on other conifer species such as Scots pine (Pinus sylvestris), European silver fir (Abies alba), and larch (Larix), and non-native Colorado blue spruce (Picea pungens) and Sitka spruce (P. sitchensis). Reports of the latter three European tree species as hosts should be interpreted with caution because the sources are old and unaccompanied by other supporting information. The beetle prefers to infest mature to overmature trees with diameters greater than 30 centimetres.

Host parts affected

Inner bark and outer wood of trunk

Symptoms and signs

The most obvious indications of attack by this insect are streams of resin dripping along the trunk of the infested tree and oval-shaped holes in the bark, 4 to 6 millimetres across (exit holes where adult beetles emerge). Depending on the number of times the tree has been infested by brown spruce longhorn beetle, the crown may appear green and healthy, or thinned and desiccated. If the bark is stripped from the tree, there will be networks of larval feeding galleries in the phloem that lightly score the sapwood and are packed with frass (excrement). There may also be pupal cells that extend 2 to 4 centimetres into the sapwood. These cells appear L-shaped when the wood is cut longitudinally.

Larvae are somewhat flattened grubs. They are creamy white in colour, legless, and 15 to 25 millimetres long. Adult beetles have 10 to 15 millimetres flattened bodies. They have a dark brown or black head and thorax as well as tan, brown, or reddish-brown elytra (wing covers). There is often a lighter brown band across the base of the elytra near the thorax. The antennae of adults are red-brown and about half of their body length. Their legs are dark brown.

This introduced species is very similar in appearance to our native species, eastern larch borer (Tetropium cinnamopterum). A specialist is required to make a positive identification.

Life cycle

In the spring, female beetles lay eggs in the bark of standing or recently felled trees. Eggs are usually laid singly, but sometimes in clusters of up to 10 eggs. Larvae hatch 10 to 14 days later and bore into the phloem to feed, producing a network of irregular tunnels packed with sawdust-like frass. After about two months, the larvae are full-grown. This insect mostly overwinters as prepupal larvae either under the bark or in characteristic L-shaped pupal cells in the sapwood. Pupation occurs in spring and adults emerge about 14 days later. The adults live about two weeks and are typically observed from June to August. Both males and females are strong flyers. Although restricted to Nova Scotia and New Brunswick, this beetle would likely have one generation per year across most of the range of spruces in Canada.

The fungus, Ophiostoma tetropii, is often associated with the beetle and can be found in the beetle’s galleries in the host. The role of this fungus in the beetle’s life cycle and its pathogenicity are not well known.

Because this invasive species is closely related to eastern larch borer, it is attacked by some of the same natural parasitic wasps as the native species: Rhimphoctona macrocephala (Ichneumonidae) and Wroughtonia occidentalis (Braconidae). Woodpeckers will also feed on brown spruce longhorn beetle.

Damage

Damage to trees from this insect in Canada is currently limited. Research in Nova Scotia has shown that red and white spruce with reduced growth rates and low vigour are more vulnerable to colonization and mortality than faster growing, more vigorous trees. Future climate change could result in increased wind-blown and drought stressed spruce trees, making them more susceptible to attack and establishment by this beetle. In its native range, it generally attacks weakened or recently felled trees and has occasionally reached outbreak levels when large numbers of spruce trees have been weakened by wind damage or defoliation by other insects. In Europe, outbreaks have the potential to persist for a decade and cause damage across extensive tracts of conifer forest, most commonly in stands of Norway spruce more than 50 years of age.

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 (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 for any particular pest.

The spread rate of brown spruce longhorn beetle has been relatively slow. Possible reasons for slow spread may be due to mating errors with the native eastern larch borer, which uses the same pheromone, and regulation by natural enemies.

Maintaining a healthy and vigorous forest through proper forest management practices is one of the best ways to prevent the spread and establishment of brown spruce longhorn beetle. Such activities include removing trees that have been blown down, broken, or otherwise weakened or damaged; cutting and destroying (burning or chipping) infested trees that show signs and symptoms of beetle attack; and processing cut logs during late fall or winter to help reduce the risk of further beetle spread.

Regulatory controls imposed by the Canadian Food Inspection Agency (CFIA) is a management tactic to prevent the range expansion of the beetle by restricting the movement of spruce materials outside of the regulated areas. Educating as many people as possible to be able to recognize the signs and symptoms of beetle attack and reporting sightings are excellent ways to prevent the spread. Prohibiting the movement of firewood is extremely important to limiting the spread of brown spruce longhorn beetle and other invasive forest insects.

Beetles, such as brown spruce longhorn beetle, that feed on phloem and wood within trees are difficult to control with pesticides. Pesticides registered for use against brown spruce longhorn 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 beetle. 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

Anderson, J.L.; Heard, S.B.; Sweeney, J.; Pureswaran, D.S. 2022. Mate choice errors may contribute to slow spread of an invasive Eurasian longhorn beetle in North America (Coleoptera: Cerambycidae). Neobiota 71: 71–89. https://doi.org/10.3897/neobiota.71.72843

Canadian Council of Forest Ministers. 2014. Pest risk analysis: risk assessment of the threat of brown spruce longhorn beetle to Nova Scotia forests. Canadian Council of Forest Ministers. Ottawa, Ontario. 85 p.   https://www.ccfm.org/releases/risk-assessment-of-the-threat-of-brown-spruce-longhorn-beetle-to-nova-scotia-forests-2014/ Accessed October 2024.

Dearborn, K.W.; Heard, S.B; Sweeney. J.D.; Pureswaran, D.S 2016. Displacement of Tetropium cinnamopterum (Coleoptera: Cerambycidae) by its invasive congener Tetropium fuscum. Environmental Entomology 45(4): 848–854. https://doi.org/10.1093/ee/nvw045

Flaherty, L.; Sweeney, J.D.; Pureswaran, D.; Quiring, D.T. 2011. Influence of host tree condition on the performance of Tetropium fuscum (Coleoptera: Cerambycidae). Environmental Entomology 40(5): 1200–1209. https://doi.org/10.1603/EN11114

Harrison, K.J.; Smith, G.A. 2013. The discovery of Ophiostoma tetropii with the brown spruce longhorn beetle (Tetropium fuscum) in Halifax, Canada. Pages 213–217 in K.A. Seifert, Z.W. De Beer, and M.J. Wingfield, editors. The Ophiostomatoid fungi: expanding frontiers. CBS Biodiversity Series 12, CBS-KNAW Fungal Biodiversity Centre. Utrecht, The Netherlands.

Jacobs, K.; Seifert, K.A.; Harrison, K.J.; Kirisits, T. 2003. Identity and phylogenetic relationships of ophiostomatoid fungi associated with invasive and native Tetropium species (Coleoptera: Cerambycidae) in Atlantic Canada. Canadian Journal of Botany 81(4): 316–329. https://doi.org/10.1139/b03-025

Kimoto, T.; Duthie-Holt, M.; Dumouchel, L. 2006. Exotic forest insect guidebook. Canadian Food Inspection Agency. 120 p.

MacKinnon, W.E. 2012. Living with the brown spruce longhorn beetle. Atlantic Forestry Review 19(1): 36–39.

O'Leary, K.; Hurley, J.E.; Mackay, W.; Sweeney, J. 2003. Radial growth rate and susceptibility of Picea rubens Sarg. to Tetropium fuscum (Fabr.). Pages 107–114 in M.L. McManus and A.M. Liebhold, editors. Proceedings: Ecology, Survey and Management of Forest Insects. 1–5 September 2002. Krakow, Poland. United States Department of Agriculture, Forest Service, Northeastern Research Station. General Technical Report NE-311.

Ramsfield, T.D. 2016. Evolving symbioses between insects and fungi that kill trees in Canada: new threats associated with invasive organisms. The Canadian Entomologist 148(S1): S160–S169. https://doi.org/10.4039/tce.2015.65

Smith, G.A.; Humble, L.M. 2000. The brown spruce longhorn beetle. Natural Resources Canada, Canadian Forest Service, Pacific Forestry Centre, Victoria, British Columbia, Exotic Forest Pest Advisory 5. 4 p. https://ostrnrcan-dostrncan.canada.ca/entities/publication/51cf4563-66a2-458b-8d2a-e66dda0b8a8d?fromSearchPage=true

Sweeney, J.D.; Silk, P.J.; Rhainds, M.; MacKay, W.; Hughes, C.; Van Rooyen, K.; MacKinnon, W.; Leclair, G.; Holmes, S.E.; Kettela, E.G. 2017. First report of mating disruption with an aggregation pheromone: a case study with Tetropium fuscum (Coleoptera: Cereambycidae). Journal of Economic Entomology 110(3): 1078–1086. https://doi.org/10.1093/jee/tow308

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Photos

Adult female of brown spruce longhorn beetle with its ovipositor extended.

Jon Sweeney

Adult male brown spruce longhorn beetle.

Jon Sweeney