Dryocoetes confusus (western balsam bark beetle)
- Taxonomic Tree
- Distribution Table
- Risk of Introduction
- Hosts/Species Affected
- Host Plants and Other Plants Affected
- Growth Stages
- List of Symptoms/Signs
- Biology and Ecology
- Natural enemies
- Notes on Natural Enemies
- Means of Movement and Dispersal
- Plant Trade
- Threatened Species
- Risk and Impact Factors
- Detection and Inspection
- Similarities to Other Species/Conditions
- Prevention and Control
- Distribution Maps
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PicturesTop of page
IdentityTop of page
Preferred Scientific Name
- Dryocoetes confusus Swaine, 1912
Preferred Common Name
- western balsam bark beetle
Other Scientific Names
- Dryocoetes abietis Hopkins, 1915
International Common Names
- English: bark beetle, mountain balsam; bark beetle, western balsam; mountain balsam bark beetle
- French: scolyte du sapin de l'ouest; scolyte du sapin du l'ouest
- DRYOCN (Dryocoetes confusus)
Taxonomic TreeTop of page
- Domain: Eukaryota
- Kingdom: Metazoa
- Phylum: Arthropoda
- Subphylum: Uniramia
- Class: Insecta
- Order: Coleoptera
- Family: Scolytidae
- Genus: Dryocoetes
- Species: Dryocoetes confusus
DescriptionTop of page
The eggs are smooth, oval, white and translucent.
The larvae are similar to scolytid larvae in general. They are white, legless and slightly curved. They have a lightly sclerotized, pale-tan head capsule and are 3-4 mm long when mature (Garbutt, 1992). See Thomas (1957) for generic characters of Dryocoetes larvae.
The pupae are exarate, usually whitish and 3-4 mm long. They have prominent wing pads and a distinct head, thorax and abdomen.
The adults are cylindrical and 3.4-4.3 mm long. They are shiny, ranging in colour from yellow-brown to reddish-brown to black and clothed with erect setae. The head is only slightly visible from above, the frons is convex and distinctive in females, with a circular patch of very dense reddish-brown to yellow hair-like setae, as opposed to sparsely pubescent in males. The mouthparts are directed downwards. The antennae are geniculate and capitate, with the antennal club wider than it is long and the basal corneous part occupying little more than half the total length. The pronotum is 1.1 times wider than it is long and evenly convex above. The elytra are 1.6 times longer than they are wide and abruptly rounded posteriorally. The elytral declivity is convex and lacking declivital spines. For generic and specific keys including Dryocoetes, and detailed specific descriptions, see Bright (1976) and Wood (1982), see also Bright (1963) for a more detailed description of morphology.
DistributionTop of page
Distribution TableTop of page
The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.Last updated: 17 Feb 2021
|Continent/Country/Region||Distribution||Last Reported||Origin||First Reported||Invasive||Reference||Notes|
|United States||Present, Localized|
Risk of IntroductionTop of page
Hosts/Species AffectedTop of page
Host Plants and Other Plants AffectedTop of page
|Abies amabilis (Pacific silver fir)||Pinaceae||Other|
|Abies balsamea (balsam fir)||Pinaceae||Other|
|Abies bifolia x Abies lasiocarpa||Pinaceae||Main|
|Abies concolor (Rocky Mountain white fir)||Pinaceae||Other|
|Abies grandis (grand fir)||Pinaceae||Main|
|Abies lasiocarpa (rocky mountain fir)||Pinaceae||Main|
|Picea engelmannii (Engelmann spruce)||Pinaceae||Other|
Growth StagesTop of page
SymptomsTop of page
List of Symptoms/SignsTop of page
|Stems / gummosis or resinosis|
|Stems / internal discoloration|
|Stems / internal feeding|
|Stems / mycelium present|
|Stems / visible frass|
|Whole plant / cut at stem base|
|Whole plant / discoloration|
|Whole plant / frass visible|
|Whole plant / internal feeding|
|Whole plant / plant dead; dieback|
|Whole plant / uprooted or toppled|
Biology and EcologyTop of page
Attacking males excavate a nuptial chamber in the phloem, and accept up to five females, which mine egg galleries radiating out from the nuptial chamber (Swaine, 1918; Garbutt, 1992). Both nuptial chamber and egg galleries often score the xylem tissue, leaving a characteristic star-shaped etching on the exposed wood of previously infested hosts. Eggs are laid on both sides of the egg galleries and the larvae bore irregular mines in the phloem. The life cycle usually takes 2 years (Mathers, 1931), although in warm conditions D. confusus may be univoltine (Furniss and Carolin, 1977; Garbutt, 1992). Adults that have attacked in the spring and summer overwinter in extensions of the nuptial chamber (males) and egg galleries (females) and resume mating and oviposition in the following spring. In mid-summer they may re-emerge to establish a second brood on the same tree or on a new host. Larvae and eggs produced in the first summer overwinter in the phloem and resume development in the following spring. There are four instars (Stock, 1981), which remain in the brood host for a second winter. Brood from the second spring and summer of oviposition are offset by an addition year, so that newly matured adults emerge from the same host for two successive years.
Natural enemiesTop of page
|Natural enemy||Type||Life stages||Specificity||References||Biological control in||Biological control on|
Notes on Natural EnemiesTop of page
Means of Movement and DispersalTop of page
Plant TradeTop of page
|Plant parts liable to carry the pest in trade/transport||Pest stages||Borne internally||Borne externally||Visibility of pest or symptoms|
|Bark||adults; eggs; larvae; nymphs; pupae||Yes||Pest or symptoms usually visible to the naked eye|
|Stems (above ground)/Shoots/Trunks/Branches||adults; eggs; larvae; nymphs; pupae||Yes||Pest or symptoms usually visible to the naked eye|
ImpactTop of page
Threatened SpeciesTop of page
|Threatened Species||Conservation Status||Where Threatened||Mechanism||References||Notes|
|Tamiasciurus hudsonicus grahamensis (Mount Graham red squirrel)||USA ESA listing as endangered species||Arizona||Ecosystem change / habitat alteration||US Fish and Wildlife Service (2007)|
Risk and Impact FactorsTop of page
- Ecosystem change/ habitat alteration
Detection and InspectionTop of page
Similarities to Other Species/ConditionsTop of page
Prevention and ControlTop of page
Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.D. confusus infestations can be controlled by sanitation-salvage harvesting (Garbutt, 1992), which removes infested trees from a stand and kills the beetles during the manufacturing process in a saw mill or pulp mill. Before harvesting, infestations can be contained and concentrated by baiting uninfested trees with the aggregation pheromone exo-brevicomin (Stock et al., 1994; Greenwood and Borden, 2000). There is no other published information on the control of this species.
The exclusion of any unseasoned logs, lumber and dunnage at ports of entry is probably adequate to prevent introductions of D. confusus or Ceratocystis dryocoetidis. A requirement for all lumber to be kiln-dried would be a reasonable additional precaution. A potential problem could arise if traps baited with racemic exo-brevicomin are used as a monitoring tool for tree-killing Dendroctonus species at ports of entry. Although the pheromone for D. confusus is a 9:1 blend of (+)-exo-brevicomin to (+)-endo-brevicomin (Camacho et al., 1993), both D. confusus and Dryocoetes autographus respond to racemic exo-brevicomin (Jeans-Williams, 1999). Unless catches of Dryocoetes species in monitoring traps baited with exo-brevicomin are identified to species, it is thus possible that captured D. confusus could be mistaken for D. autographus, or may remain undetected among a more numerous catch of D. autographus.
ReferencesTop of page
Bright DE Jr, 1976. The insects and arachnids of Canada. Part 2. The bark beetles of Canada and Alaska. Coleoptera: Scolytidae. The insects and arachnids of Canada. Part 2. The bark beetles of Canada and Alaska. Coleoptera: Scolytidae. Canada Department of Agriculture. Ottawa Canada, 241 pp.
Bright DE, 1963. Bark beetles of the genus Dryocoetes (Coleoptera: Scolytidae) in North America. Annals of the Entomological Society of America, 56:103-115.
Camacho AD, Pierce HD Jr, Borden JH, 1993. Geometrical and optical isomerism of pheromones in two sympatric Dryocoetes species (Coleoptera: Scolytidae), mediates species specificity and response level. Journal of Chemical Ecology, 19(10):2169-2182
Camacho AD, Pierce HDJr, Borden JH, 1998. Host compounds as kairomones for the western balsam bark beetle Dryocoetes confusus Sw. (Col., Scolytidae). Journal of Applied Entomology, 122(6):287-293; 49 ref.
EPPO, 2014. PQR database. Paris, France: European and Mediterranean Plant Protection Organization. http://www.eppo.int/DATABASES/pqr/pqr.htm
Farris SH, 1969. Occurrence of mycangia in the bark beetle Dryocoetes confusus (Coleoptera: Scolytidae). The Canadian Entomologist, 101:527-532.
Furniss RL, Carolin VM, 1977. Western Forest Insects. Washington DC, USA: US Department of Agriculture Forest Service, Miscellaneous Publication No. 1339.
Garbutt R, 1992. Western balsam bark beetle. Victoria, British Columbia, Canada: Forestry Canada, Forest Pest Leaflet Number 64.
Gibson K, Kegley S, Oakes B, 1997. Western balsam bark beetle activity and flight periodicity in the Northern Region. Missoula, Montana, USA: US Department of Agriculture, Forest Service. Cooperative Forestry and Forest Health Protection Report Number 97-3.
Greenwood ME, Borden JH, 2000. Co-baiting for spruce beetles, Dendroctonus rufipennis, and western balsam bark beetles, Dryocoetes confusus (Coleoptera: Scolytidae). Canadian Journal of Forest Research, 30(1):50-58; 30 ref.
Hunt RS, 1993. ABIES. In: Morin NR, ed. Flora of North America North of Mexico, Volume 2. New York, USA: Oxford University Press, 354-362.
Jeans-Williams NL, 1999. Evaluation of pheromone baits for the western balsam bark beetle, Dryocoetes confusus Swaine (Coleoptera: Scolytidae) and partial elucidation of the pheromone for Dryocoetes autographus Ratzeburg. Master of Pest Management Thesis. Burnaby, British Columbia, Canada: Simon Fraser University.
Kendrick WB, Molnar AC, 1965. A new Ceratocystis and its Verticicladiella imperfect state associated with the bark beetle Dryocoetes confusus on Abies lasiocarpa. Canadian Journal of Botany, 43:39-43.
Molnar AC, 1965. Pathogenic fungi associated with a bark beetle on alpine fir. Canadian Journal of Botany, 43:563-570.
Smith IM, McNamara DG, Scott PR, Holderness M, 1997. Quarantine pests for Europe. Second Edition. Data sheets on quarantine pests for the European Union and for the European and Mediterranean Plant Protection Organization. Quarantine pests for Europe. Second Edition. Data sheets on quarantine pests for the European Union and for the European and Mediterranean Plant Protection Organization., Ed. 2:vii + 1425 pp.; many ref.
Stock AJ, 1981. The western balsam bark beetle, Dryocoetes confusus Swaine: secondary attraction and biological notes. Master of Science Thesis. Burnaby, British Columbia, Canada: Simon Fraser University.
Stock AJ, 1991. The western balsam bark beetle, Dryocoetes confusus Swaine: impact and semiochemical-based management. PhD Thesis. Burnaby, British Columbia, Canada: Simon Fraser University.
Stock AJ, Borden JH, Pratt TL, 1994. Containment and concentration of infestations of the western balsam bark beetle, Dryocoetes confusus (Coleoptera: Scolytidae), using the aggregation pheromone exo-brevicomin. Canadian Journal of Forest Research, 24(3):483-492
Swaine JM, 1918. Canadian bark beetles, Part II. Preliminary classification, with an account of the habits and means of control. Ottawa, Ontario, Canada: Printer to the King's Most Excellent Majesty. Dominion of Canada, Department of Agriculture, Entomological Branch, Technical Bulletin Number 14.
Thomas JB, 1957. The use of larval anatomy in the study of bark beetles (Coleoptera: Scolytidae). The Canadian Entomologist, Supplement Number 5, 3-45.
Westfall J, 2002. 2001 Summary of forest health conditions in British Columbia. Victoria, British Columbia, Canada: British Columbia Ministry of Forests, Forest Practices Branch.
Whitney HS, Ritchie DC, Borden JH, Stock AJ, 1984. The fungus Beauveria bassiana (Deuteromycotina: Hyphomycetaceae) in the western balsam bark beetle, Dryocoetes confusus (Coleoptera: Scolytidae). Canadian Entomologist, 116(10):1419-1424
Bright D E Jr, 1976. The insects and arachnids of Canada. Part 2. The bark beetles of Canada and Alaska. Coleoptera: Scolytidae. In: The insects and arachnids of Canada. Part 2. The bark beetles of Canada and Alaska. Coleoptera: Scolytidae. Ottawa, Canada: Canada Department of Agriculture. 241 pp.
Burns K S, Klopfenstein N B, Kim M S, 2016. First report of the Armillaria root disease pathogen, Armillaria sinapina, on subalpine Fir (Abies lasiocarpa) and quaking aspen (Populus tremuloides) in Colorado. Plant Disease. 100 (1), 217-218. DOI:10.1094/PDIS-07-15-0837-PDN
CABI, Undated. CABI Compendium: Status as determined by CABI editor. Wallingford, UK: CABI
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