14.5 Status of species harmful to forests in the NWT

Last Updated: 
June 1, 2015

This indicator tracks species of insects and spiders present in the NWT considered alien, invasive, or pests which can be harmful to our plant communities including our forests.

This indicator uses information collected for the NWT General Status Ranking Program (GSRP)1 and from a project called: Risk Analysis and Management of Alien Plant and Insects in the Northwest Territories, funded by Environment Canada, Indian and Northern Affairs Canada, GNWT Environment and Natural Resources, Parks Canada, and Agriculture Canada. Additional information on forest pest insects was obtained from forest experts in ENR Forest Management, and NRCAN’s webpage: Forest Invasive Alien Species in Canada2.

The indicator tracks species using three definition codes.

Alien: species (plants, animals, and micro-organisms) that have been introducted as a result of human activities; same definition as in the GSRP.

New-range extension: species newly discovered in the NWT, for which there is evidence of recent range extension. This definition helps to track 'true' new speices to the NWT, as their pattern of distribution changes.  Same definition as change codes 'new species' in the GSRP. Uncertanties as noted.

Invasive: Alien species that spread and threaten the ecosystems, and by extension the environment, the economy or society. All invasive species are alien. For native species that have invasive-like habits, see the 'pest' definition. Some alien insects are deemed forest invasive, as they feed on trees and spread over large tracks of NWT forest and can change an entire landscape for many years.

Pest: Native or alien species that can spread, and at least in some years, can threaten a component of an ecosystem that has economic value (ex: timber)

NWT Focus

Changes in the number of alien, invasive, or pest species of insects and spiders in the NWT provide an indicatorof ecosystem change, including habitat and climate change. Changes in the number of alien insects and spiders are also monitored as their presence and abundance may affect the status of wild species native to the NWT.

Arthropods (insects, spiders) form the most diverse part of NWT’s biodiversity. It is estimated that thousands of species can be found in NWT ecosystems. Insects and spiders have adapted to harsh climates and the great majority of NWT’s species are present year-round, i.e., they are not migratory. The number of alien and pest species present further south is much greater. Changes in the northern environment may favour advance of these species into our ecosystems.

Current view: status and trend

Currently 11 alien species of insects and no spiders are known to be present in the NWT. Most of these species have been noted in the NWT for more than 50 years, but the extent of their distribution is unknown. Two of these alien species (the Larch Sawfly and the Amber-marked Birch Leafminer) are subject to monitoring programs.

Common Name Scientific species name Definition Code Comments
Lepidoptera  Butterflies and Moths
Cabbage White
(Cabbage Worm)
Pieris rapae Alien Introduced to NA in Quebec City circa 1860 from Eurasia; quickly spread to gardens across NA, but not recorded in NWT until 2001 (Yellowknife, Fort Simpson, Yohin Lake in Nahanni National Park Reserve); to be looked for elsewhere. Hosts: mustard family2.
Rusty Tussock Moth Orgyia antiqua Alien; Invasive; Forest Pest Present in the NWT, extent unknown. Considered invasive and a pest in Canada but does little damage in the NWT. Hosts: spruces and pines2.
Birch-aspen Leafroller Moth Epinotia solandriana Alien; Minor invasive Present in the NWT as early as the 1960s. Considered a minor invasive. Hosts: trembling aspens, alders and yellow birch2.
Hemiptera - Coccidae  True Bugs - Wax Scales

Small Sprucebud Scale
Physokermes hemicryphus (P. piceae) Alien; Invasive Present in the NWT3, but extent is unknown. Considered invasive in Canada. Host: spruces.
Hemiptera - Adelgidae  True Bugs - Adelgids
Larch Woolly Adelgid Adelges laricis Alien; Invasive Present in the NWT, but extent is unknown. Requires both spruce and larch (tamarack) for development. Origin: Europe. Considered invasive in Canada..
Hymenoptera - Tenthredinidae  Sawflies
Larch Sawfly Pristiphora erichsonil Alien; Invasive First observed in Canada in 18824; from Europe. Quickly spread to larch and tamarack forests across the US and Canada. Reached the North in the 1960s. Now present in various densities across all forested ecozones in the NWT. GNWT Forest Management and Canadian Forest Service monitor outbreaks annually.
Striped Alder Sawfly Hemichroa crocea Alien; Invasive Present in the NWT, extent is unknown. Larvae feed on alder and birch leaves. Origin: Eurasia. Considered invasive in Canada.
Birch Leaf Edgeminer Scolioneura betuleti (Heterarthrus nemoratus) Alien; Pest First noted in NWT in 2003 in Hay River town, Hay River Beach, Yellowknife5. First observed in Canada in 19058. Introduced from Europe. Hosts: alders and birches. Not considered invasive, but a pest.
Amber-marked Birch Leafminer Profenusa thomsoni Alien; Invasive; Pest First noted in the NWT in 1994; Abundant in Yellowknife, extending into the surrounding wild birch stands, mostly along the Ingraham Trail and other roads. Present in Hay River, and other areas in the South Slave region5. Introduced in 1948 from Europe, now present across Canada2. Turns trees brown in mid-summer and is of public concern for aesthetic reasons, but in the future may also affect large tracks of birches outside built-up areas as in Alaska9. Considered invasive and a pest. Hosts: trembling aspens, alders and yellow birch2.
European alder leafminer Fenusa dohrnii Alien Observed in wild stands near Hay River and Behchoko, Fort Resolution, Fort Simpson, and Fort Liard in 2003. Attacked speckled alders but not green alder. Entire extent in the NWT is unknown but suspected that it is expanding largely without assistance from humans. First observed in NA in 1890s5.
Birch Leafminer Fenusa pumila (Fenusa pusilla) Alien; Invasive; Pest First noted in the NWT in 2003 in Hay River5. From Europe. Introduced to NA in 1923, was observed in Canada in 1929, now present across Canada. Considered invasive and a pest. Hosts: birches.
Coleoptera - Chrysomelidae Beetles – Leaf Beetles
Poplar Blackmine Beetle Zeugophora scutellaris Alien; Invasive Present in the NWT, extent is unknown. Origin is Eurasia. Hosts: poplars and aspen. Considered invasive in Canada.

Source: Information from the NWT General Status Ranking Program and as referenced.
Butterflies photos courtesy of The Butterflies of Canada by Ross A. Layberry, Peter W. Hall, and J. Donald Lafontaine. University of Toronto Press; 1998. (web version).

Larch sawfly larva photo courtesy of University of Georgia

Rusty Tussock Moth photo: adult: USDA Forest Service Archives, USDA Forest Service, www.forestryimages.org
Caterpillar: Connecticut Agricultural Experiment Station Archives, Connecticut Agricultural Experiment Station, www.forestryimages.org
Birch-aspen Leafroller Moth photo courtesy of Edward H. Holsten, USDA Forest Service, Bugwood.org, obtained from www.forestryimages.org.
AMBLM and Birch Leafminer: Thérèse Arcand, Natural Resources Canada, Canadian Forest Service, Laurentian Forestry Centre Small Sprucebud Scale: Edward H. Holsten, USDA Forest Service, United States, Bugwood.org
Larch Woolly Adelgid: Louis-Michel Nageleisen, Département de la Santé des Forêts, Bugwood.org
Striped Alder Sawfly: USDA Forest Service - Alaska Archive, USDA Forest Service, Bugwood.org
Poplar Blackmine Beetle : Whitney Cranshaw, Colorado State University, Bugwood.org
European alder leafminer: Whitney Cranshaw, Colorado State University, Bugwood.org
Mountain pine beetle photo: UGA0949030 from www.forestryimages.org

In addition to alien species, some native insects such as the Spruce budworm (Choristoneura fumiferana), tent caterpillars (Malacosoma spp.) and bark beetles (Scolytidae) can significantly damage NWT forests. The most important pest species is spruce budworm, which has been monitored in the NWT since the 1950s. In the late 1990s and early 2000, there was an unprecedented outbreak of spruce budworm population along the Mackenzie River Valley. However, by 2002 the population started to decline. In 2005, the population returned to medium levels and has stabilized since. ENR's Forest Management Division conducts annual Forest Health Surveys along areas identified as high risk, i.e., along major rivers and waterways or uplands and hill slopes. Over 6,000 km of survey routes are monitored each summer to detect defoliation caused by insect pests that include aspen serpentine leafminer (Phyllocnistic populiella), willow blotch leafminer (Micrurapteryx salicifoliella) and forest tent caterpillar (Malacosoma disstria).

Looking forward

NWT residents can help determine the current distribution of alien species in the NWT by reporting their presence to ENR offices. Official species lists have been compiled for the NWT General Status Ranking Program since 20001. Species lists include butterflies, tiger beetles, dragonflies and damselflies. Official species lists for NWT spiders, some groups of beetles, moths, deer flies, horse flies, bees, black flies and mosquitoes are being developed and will be available for tracking by this indicator in 2010. Updates on new species of insects are possible only through the contributions of visiting entomologists, tourists, and NWT residents interested in NWT biodiversity.

Looking around

The mountain pine beetle (Dendroctonus ponderosae), one of the more intensely monitored forest pest insects in western North America, is creating unprecedented damage to pine forests in British Columbia and Alberta. The advances of the species are tracked by ENR forest experts. The beetle was observed in the NWT for the first time in summer 2012. A mountain pine beetle pest risk analysis for the NWT pine forests was prepared in 2013 indicating low risk of establishment and spread by 2020 and moderate to high risk by 20706,7. Since 2014,  dedicated mountain pine beetle surveys have been in place to monitor for this new invasive pest.

Find out more


Found an error or have a question? Contact the team at NWTSOER@gov.nt.ca.


Ref. 1. Working Group on General Status of NWT Species. Current. NWT General Status Ranking Program.

Ref. 2. Natural Resources Canada. Current. Forest Invasive Alien Species of Canada

Ref. 3. Furniss, M.M. 2004. Observations on an introduced bud scale, Physokermes hemicryphus (Homoptera: Coccidae), infesting Norway spruce in Idaho. Can. J. for Res. 34: 1348-1352.

Ref. 4. US Department of Agriculture. 2001. The Larch Sawfly, Leaflet R10-TP-101 ed. 2001.

Ref. 5. Digweed, S.C., and D.W. Langor. 2005. Distributions of leafmining sawflies (Hymenoptera: Tenthredinidae) on birch and alder in northwestern Canada. Can. Entomologist 136: 727-731.

Ref. 6. Hodge, J. 2014. Mountain pine beetle pest rish analysis for Northwest Territories pine forests. Forest Management Division, Environment and Natural Resources.

Ref. 7. Nealis, V. and B. Peter. 2008. Risk assessment of the threat of mountain pine beetle to Canada's boreal and eastern pine forests. Natural Resources Canada. 45pp. 

Ref. 8. US Department of Agriculture (USDA). The Larch Sawfly in Leaflet R10-TP-101 ed. 2001. 

Ref. 9. Snyder, C., C.J.K. MacQuarrie, K. Zogas, J.J. Kruse, and J. Hard. 2007. Invasive species in the last frontier: distribution and phenology of birch leaf mining sawflies in Alaska. J. of Forestry 105:113-115.

Updated: June 1, 2015