Dendroctonus pseudotsugae (Douglas-fir beetle)
- Summary of Invasiveness
- Taxonomic Tree
- Notes on Taxonomy and Nomenclature
- 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
- Pathway Vectors
- Plant Trade
- Wood Packaging
- Environmental Impact
- 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
- Dendroctonus pseudotsugae Hopkins, 1905
Preferred Common Name
- Douglas-fir beetle
International Common Names
- English: beetle, Douglas fir; Douglas fir beetle
- French: dendroctone du Douglas; dendroctone du sapin Douglas
Local Common Names
- Germany: Douglasien Riesenbastkaefer; Riesenbastkaefer, Douglasien-
- DENCPS (Dendroctonus pseudotsugae)
Summary of InvasivenessTop of page This insect has not established outside its geographic range and therefore can only be considered as potentially invasive.
Taxonomic TreeTop of page
- Domain: Eukaryota
- Kingdom: Metazoa
- Phylum: Arthropoda
- Subphylum: Uniramia
- Class: Insecta
- Order: Coleoptera
- Family: Scolytidae
- Genus: Dendroctonus
- Species: Dendroctonus pseudotsugae
Notes on Taxonomy and NomenclatureTop of page The Douglas-fir beetle was described in 1905 by AD Hopkins, from specimens collected near Grants Pass, Oregon, USA. It has not undergone changes in nomenclature since its original description (Wood, 1963, 1982).
DescriptionTop of page Eggs
Scolytidae eggs are smooth, ovoid, white and translucent. Douglas-fir beetle eggs are about 1.02 mm long and laid separately, in niches along the egg gallery, which is packed tightly with frass.
Scolytidae larvae are all similar in appearance and difficult to separate. They are white, 'C'-shaped and legless. The head capsule is lightly sclerotized and amber, with dark, well-developed mouthparts. Each abdominal segment has two to three tergal folds and the pleuron is not longitudinally divided. The larvae do not change as they grow. There are four larval instars and mature larvae are 4-6 mm long.
Scolytid pupae are white and mummy-like. They are exarate, with legs and wings free from the body. Some species have paired abdominal urogomphi. The elytra are either rugose or smooth, and sometimes they have a prominent head and thoracic tubercles.
The adults are 4.6 to 7 mm long (average of 5.7 mm). The body is cylindrical, stout and dark brown, almost black, except for the elytra, which are reddish-brown. The pronotum has fine punctures and is broader than it is long. The base of the pronotum is broad and narrowed forward. The basal sides of the pronotum are straight and subparallel for two-thirds of their length. The elytral declivity is convex and steep, with elevated interstriael punctures. Interstria two is weakly impressed. The vestiture is dispersed and longer on the declivity. The longest setae are equal to the width of an interstria (Wood, 1982).
DistributionTop of page The Douglas-fir beetle occurs throughout the geographic range of its primary host, Douglas-fir, Pseudotsuga menziesii, in western North America. It can be found from southwestern Alberta (Waterton Lakes) and British Columbia, Canada, to western USA and northern Mexico, and east to western Texas (Furniss and Orr, 1978; Wood, 1982).
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.
|Continent/Country/Region||Distribution||Last Reported||Origin||First Reported||Invasive||Reference||Notes|
|China||Present||Present based on regional distribution.|
|-Anhui||Restricted distribution||Introduced||Invasive||Ciesla, 1992; CABI/EPPO, 2004|
|Canada||Restricted distribution||CABI/EPPO, 2004; EPPO, 2014|
|-Alberta||Restricted distribution||Native||Invasive||Wood, 1982; CABI/EPPO, 2004; EPPO, 2014|
|-British Columbia||Restricted distribution||Native||Invasive||Furniss & Orr, 1979; Wood, 1982; CABI/EPPO, 2004; EPPO, 2014|
|Mexico||Restricted distribution||Native||Invasive||Cibrián Tovar et al., 1995; CABI/EPPO, 2004; EPPO, 2014|
|USA||Restricted distribution||CABI/EPPO, 2004; EPPO, 2014|
|-Alaska||Absent, unreliable record||CABI/EPPO, 2004; EPPO, 2014|
|-Arizona||Restricted distribution||Native||Invasive||Wood, 1982; Ciesla and Coulston, 2002; CABI/EPPO, 2004; EPPO, 2014|
|-California||Restricted distribution||Native||Invasive||Furniss and Orr, 1978; Wood, 1982; Ciesla and Coulston, 2002; CABI/EPPO, 2004; EPPO, 2014|
|-Colorado||Restricted distribution||Native||Invasive||Wood, 1982; Ciesla and Coulston, 2002; CABI/EPPO, 2004; EPPO, 2014|
|-Idaho||Restricted distribution||Native||Invasive||Furniss and Orr, 1978; Wood, 1982; Ciesla and Coulston, 2002; CABI/EPPO, 2004; EPPO, 2014|
|-Montana||Restricted distribution||Native||Invasive||Wood, 1982; Ciesla and Coulston, 2002; CABI/EPPO, 2004; EPPO, 2014|
|-Nevada||Restricted distribution||Native||Invasive||Ciesla and Coulston, 2002; CABI/EPPO, 2004; EPPO, 2014|
|-New Mexico||Restricted distribution||Native||Invasive||Wood, 1982; Ciesla and Coulston, 2002; CABI/EPPO, 2004; EPPO, 2014|
|-Oregon||Restricted distribution||CABI/EPPO, 2004; EPPO, 2014|
|-Texas||Restricted distribution||Native||Invasive||Ollieu et al., 1968; CABI/EPPO, 2004; EPPO, 2014|
|-Utah||Restricted distribution||Native||Invasive||Ciesla and Coulston, 2002; CABI/EPPO, 2004; EPPO, 2014|
|-Washington||Restricted distribution||Native||Invasive||Furniss and Orr, 1978; Wood, 1982; Ciesla and Coulston, 2002; CABI/EPPO, 2004; EPPO, 2014|
|-Wyoming||Restricted distribution||Native||Invasive||Wood, 1982; Ciesla and Coulston, 2002; CABI/EPPO, 2004; EPPO, 2014|
Risk of IntroductionTop of page Adult Douglas-fir beetles are relatively strong fliers and can fly at least 2-3 km in search of new hosts. In addition, their small size makes it possible for them to disperse on air currents. Other life stages are confined to the cambium layer and inner bark, and are not naturally dispersed.
Pathways for human-assisted dispersal include the transport of unprocessed Douglas-fir logs or lumber, crates, pallets and dunnage, containing bark strips. It is possible that the larvae, pupae and overwintering adults could survive an ocean voyage and be introduced into a new location. However, the Douglas-fir beetle has a relatively narrow host range, and its primary host is Pseudotsuga menziesii. Therefore the probability of it becoming established is confined to areas where this species has been extensively planted (e.g. Chile, South America and western Europe) or areas where other species of Pseudotsuga occur. The only other areas where other species of Pseudotsuga occur are portions of China (Pseudotsuga sinensis) and Japan (Pseudotsuga japonica) (Farjon, 1998). Live adults were collected in Anhui Province, China, from imports of unprocessed Douglas-fir logs from the USA (Ciesla, 1992). The related North American red turpentine beetle, Dendroctonus valens, has recently been introduced to and established in, China, and has killed more than 6 million pines in recent years (Sun et al., 2003).
HabitatTop of page The Douglas-fir beetle prefers mature or over-mature forests of Douglas-fir. The attacks typically occur in trees that are stressed by root disease, drought and defoliation, or infested by the dwarf mistletoe, Arceuthobium douglasii. Wind-thrown trees can provide breeding sites for this insect, resulting in a population build-up. Subsequent generations attack standing trees.
Hosts/Species AffectedTop of page The Douglas-fir beetle attacks Douglas-fir, Pseudotsuga menziesii, throughout its range. It also produces broods in recently-cut western larch, Larix occidentalis, but not in living trees (Furniss and Orr, 1978). Its primary hosts are Pseudotsuga macrocarpa and Pseudotsuga menziesii [reported as Pseudotsuga fahaultii in northern Mexico (Farjon, 1998)] (Wood, 1982; Cibrián Tovar et al., 1995), and its secondary hosts are Larix occidentalis and Tsuga heterophylla (Wood, 1982).
Host Plants and Other Plants AffectedTop of page
Growth StagesTop of page Post-harvest, Vegetative growing stage
SymptomsTop of page Trees attacked by the Douglas-fir beetle are killed by a single generation of beetles. The first evidence of infestation is the occurrence of groups of trees with yellowish-green, yellow or red foliage. The needles on successfully infested trees begin to fade and change colour about 1 year after they have been attacked.
Reddish boring dust, caught in the bark crevasses or around the base of trees, is a typical symptom of attack by the Douglas-fir beetle. No pitch tubes are formed, but resin may exude from attacks in the upper bole (Furniss and Carolin, 1977).
The removal of bark from infested trees reveals typical gallery patterns and the presence of blue stain. Also, the white, globose fruiting bodies of the fungus, Cryptoporus volvatus, form on the outer bark in the year following attack (Furniss and Orr, 1978).
In wind-thrown trees, the galleries are generally more abundant on the shaded undersides (Furniss and Orr, 1978).
List of Symptoms/SignsTop of page
|Leaves / yellowed or dead|
|Stems / gummosis or resinosis|
|Stems / internal feeding|
|Stems / visible frass|
|Whole plant / discoloration|
|Whole plant / frass visible|
|Whole plant / internal feeding|
|Whole plant / plant dead; dieback|
Biology and EcologyTop of page Life History and Habits
The genus, Dendroctonus, consists of 19 species worldwide. Most of these occur on conifers in North and Central America. Dendroctonus armandi (native to China) and Dendroctonus micans are found in Palearctic conifer forests (Wood, 1982). Several species are important forest pests, capable of reaching epidemic levels and killing thousands of trees. The genus, Dendroctonus, contains some of the most destructive forest insects in North and Central America.
The Douglas-fir beetle has one generation per year. The broods remain in host trees and mainly overwinter as adults but also as larvae. Depending on the locality and climatic conditions, the overwintering adults usually emerge and attack new host trees from April to early June. The larvae that have overwintered complete their development and emerge in the summer. Some adults that fly in the spring re-emerge and make a second attack, usually in late June or July.
The females initiate attacks in the bark crevices of the host trees. Soon after beginning the attack, each female is joined by a male who takes over the function of removing frass from the entrance hole. Mating occurs within a few hours after the cambium is reached. After the gallery has been extended by several centimetres, the males may pack lower areas with frass, thereby plugging the entrance hole, or they may leave the gallery to search for another female.
The egg galleries are almost entirely constructed in the inner bark but are in continuous contact with the cambium. The galleries may lightly score the wood. They range in length from 12 to 30 cm but may extend to 90 cm, and are longer in wind-thrown trees. Ventilation tunnels may be placed at irregular intervals along the egg gallery. The orientation of the egg gallery is vertical, parallel to the wood grain and is straight or nearly so.
Oviposition occurs within 2 to 3 days after the initial attack. The eggs are deposited in grooves about 2-4 mm deep, along the sides of the egg gallery. They are deposited near to, but not necessarily touching, the cambium. Grooves are placed alternately on the side of the egg gallery, without overlapping, and with a few millimetres between a groove on one side of the gallery and the beginning of a groove on the opposite side of the gallery. The grooves vary in length from <1 cm to >8 cm. The eggs are deposited in the grooves in a single row and are in contact with one another. They are oriented with their long axis perpendicular to the egg gallery.
The habit of egg-orientation by D. pseudotsugae is somewhat unique among bark beetles of the genus Dendroctonus. It is believed to be associated with the fact that the larvae construct independent galleries rather than communal galleries, as is the case with other Dendroctonus species that deposit eggs in common grooves (e.g. D. micans, Dendroctonus terebrans and Dendroctonus valens).
Most D. pseudotsugae females re-emerge and can construct a second egg gallery. A single female can produce up to 160 eggs.
Under field conditions, the eggs hatch in 8 to 24 days. The newly-hatched larvae mine outward in the phloem, in individual galleries that are approximately perpendicular to the main egg gallery. These mines are visible in the inner surface of the phloem and increase in width as the larvae increase in size. There are four larval instars. During the final instar, the larvae construct pupal cells at the ends of the larval galleries. The larval cycle ranges from 19 to 72 days. The period of pupation is from 5 to 18 days (Wood, 1982).
Tree boles are infested by the Douglas-fir beetle for varying lengths, but seldom higher than a stem diameter of 15-20 cm. Other bark beetles, such as Scolytus tsugae or Pseudohylesinus nebulosus, often occur in portions of the bole that are too small in diameter for the Douglas-fir beetle. Douglas-fir beetle galleries are usually denser and brood survival is higher in the mid-portion of the infested bole. In wind-thrown trees, the egg galleries tend to be uniformly successful but are generally denser on the shaded underside of the bole (Furniss and Orr, 1978).
The Douglas-fir beetle responds to several chemicals (pheromones) that influence mating and aggregation. Frontalin or seudenol, in combination with components of Douglas-fir resin, attract flying beetles to trees. The pheromone, methylcyclohexenone, disrupts the attraction (Furniss and Orr, 1978).
The resistance of live trees to Douglas-fir beetle attack is the most important natural control factor. The climate and natural enemies also have an influence on Douglas-fir beetle populations (Furniss and Orr, 1978).
Natural enemiesTop of page
Notes on Natural EnemiesTop of page Natural enemies of the Douglas-fir beetle include parasitic and predaceous insects, nematodes, pathogens (Massey, 1966, 1967, 1969; Furniss, 1967, 1968; Weiser, 1970; Furniss and Carolin, 1977; Bellows et al., 1998) and mites. Unlike other conifer-infesting bark beetles, woodpeckers are not important predators of the Douglas-fir beetle (Furniss and Orr, 1978).
Pathway VectorsTop 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|
Wood PackagingTop of page
|Wood Packaging liable to carry the pest in trade/transport||Timber type||Used as packing|
|Loose wood packing material||Douglas-fir||Yes|
|Solid wood packing material with bark||Douglas-fir||Yes|
|Wood Packaging not known to carry the pest in trade/transport|
|Processed or treated wood|
|Solid wood packing material without bark|
ImpactTop of page The Douglas-fir beetle is a tree-killing insect and is considered to be the most important bark beetle enemy of Douglas-fir throughout its geographic range. Normally it breeds in felled, injured or diseased trees. The resulting tree mortality, from endemic levels of beetle activity, is widely scattered. This insect can reach epidemic levels and is capable of killing large numbers of trees over extensive areas. In the coastal Douglas-fir region from British Columbia, Canada, to California, USA, the outbreaks are sporadic and relatively short in duration. Usually these outbreaks develop as a result of extensive wind-throw or wildfire. In Rocky Mountain forests, the outbreaks are of a longer duration. They often develop in trees felled by wind, broken by snow or affected by drought, root disease and/or insect defoliators, such as the western spruce budworm, Choristoneura occidentalis or the Douglas-fir tussock moth, Orgyia pseudotsugata (Furniss and Carolin, 1977; Furniss and Orr, 1978).
A number of outbreaks of the Douglas-fir beetle, resulting in the death of thousands of trees, have occurred throughout the geographic range of Douglas-fir. Four outbreaks occurred in parts of western Oregon and Washington, USA, from 1950 to 1969. Another large outbreak occurred in California, USA, in 1966 and in northern Idaho, USA, from 1970 to 1973 (Furniss and Orr, 1978). Since 1979, outbreaks of the Douglas-fir beetle have been reported from Colorado, Idaho, Montana, Oregon, Washington and Wyoming, USA, and the beetle increased significantly in northern Idaho following a severe ice storm during the winter of 1996. Since this insect is known to attack trees damaged by wildfire, increased damage by this insect is expected, following the recent occurrence of unusually severe fire seasons (Ciesla and Coulston, 2002).
Environmental ImpactTop of page Widespread tree mortality, as a result of Douglas-fir beetle outbreaks, alters the forest ecosystem. In some cases, Douglas-fir forests can be replaced by less desirable species. A profusion of beetle-killed trees can alter the distribution and abundance of wildlife species by changing thermal and hiding cover. Extensive tree mortality may increase the water yield for several years following an infestation. Moreover, the dead trees remaining in the aftermath of an outbreak, are sources of fuels and can result in wildfires of increased extent and intensity.
The Douglas-fir beetle introduces fungi that accelerate the rate of decomposition of recently dead trees. It also increases access to the wood for other agents of deterioration. In the case of infestation of standing trees, the Douglas-fir beetle helps to create gaps in the forest and cause changes in species composition and structure in stands containing large Douglas-firs. Infestations often kill individual Douglas-firs that have been weakened by other biotic agents such as dwarf mistletoe, Arceuthobium douglasii, or root pathogens.
Detection and InspectionTop of page The bark surface should be inspected for boring dust. The cambium and inner bark of unprocessed logs or dunnage, crates or pallets, containing bark strips, should be inspected for the presence of galleries and insect life stages.
Similarities to Other Species/ConditionsTop of page Douglas-fir beetle adults are similar in appearance to the smaller Dendroctonus simplex and the more robust Dendroctonus rufipennis, but can be distinguished from both by their hosts. D. simplex infests Larix laricina and D. rufipennis infests various species of Picea (Wood, 1982). To ensure a positive identification, a taxonomist, with expertise in the family Scolytidae, should examine bark beetles believed to be a new introduction.
Prevention and ControlTop of page Cultural Control
Cultural control tactics include harvesting of mature and over-mature forests and periodic thinning of younger stands, to maintain vigorous growth, and reduce competition and resultant moisture stress. The rapid salvage of wind-thrown or infested trees, before the Douglas-fir beetle brood emerges, will help to reduce the hazard of additional trees becoming infested. These approaches offer the best methods of preventing or minimizing damage from the Douglas-fir beetle (Furniss and Orr, 1978).
Felled trees are usually less densely attacked than standing trees, thus the use of felled trap-trees to attract beetles is not efficient (Furniss and Orr, 1978).
Opportunities for enhancing the biological control of the Douglas-fir beetle may be limited since there is a diverse complex of natural enemies already attacking it (Bellows et al., 1998).
It is not economically or logistically feasible to chemically control Douglas-fir beetle infestations during outbreaks. In field tests, broods have been killed by sprays, which either fumigate the galleries or kill the life stages by contact. However, the cost of these operations is high and of questionable effectiveness (Furniss and Orr, 1978).
Preventative sprays, designed to protect high-value trees in developed recreation areas or near home sites, have not been developed for the Douglas-fir beetle.
Attractant pheromones, in combination with volatile components of Douglas-fir resin, can attract flying beetles to trees. In some cases, the anti-aggregating pheromone, methocyclohexenone (MCH) has been used to prevent the colonization of fallen material and limit Douglas-fir beetle population growth. MCH has also been shown to be effective in preventing attacks on standing trees. This technique is usually used when small areas of high-value trees need protection (Furniss and Orr, 1978).
Field monitoring of Douglas-fir beetle infestations consists of aerial and ground surveys, designed to locate groups of dead and dying trees, and confirm the presence of the insect. These surveys are conducted at least annually, over most of the forests in western North America with a Douglas-fir component.
Integrated Pest Management
The key elements of an integrated pest management programme for the Douglas-fir beetle consist of:
- Monitoring forests for the presence of infestations.
- Management of forests to keep them in a healthy growing condition.
- Rapid salvage and processing of damaged trees, following windstorms, wildfires or other natural disasters.
The anti-attractant pheromone, methycyclohexenone, has shown some promise in reducing the number of attacks by the Douglas-fir beetle in wind-thrown trees.
However, many forests susceptible to Douglas-fir beetle damage are located in remote, inaccessible areas with limited access, or have special classifications (e.g. National Park, Monument, Wilderness area, or Wild and scenic river), which preclude forest management. This makes implementation of pest management programmes logistically difficult, expensive or otherwise unrealistic. Consequently, despite the availability of effective pest management tactics, the Douglas-fir beetle continues to be a major pest of Douglas-fir forests in western North America.
ReferencesTop of page
Cibrián Tovar D, Méndez Montiel JT, Campos Bolaños R, Yates III HO, Flores Lara JE, 1995. Forest Insects of Mexico. Chapingo, México: Universidad Autonoma Chapingo. Subsecretaria Forestal y de Fauna Silvestre de la Secretaria de Agricultura y Recursos Hidraulicos, México. United States Department of Agriculture, Forest Service, USA. Natural Resources Canada, Canada. North American Forestry Commission, FAO, Publication 6.
Ciesla WM, Coulston J, 2002. Report of the United States on the criteria and indicators for sustainable management of temperate and boreal forests of the United States, Criterion 3 - Maintenance of ecosystem health and vitality, Indicator 15, Area and percent of forest affected by processes or agents beyond the range of historic variation. USDA Forest Service, On line: http://www.fs.fed.us/research/sustain/.
EPPO, 2014. PQR database. Paris, France: European and Mediterranean Plant Protection Organization. http://www.eppo.int/DATABASES/pqr/pqr.htm
Farjon A, 1998. World checklist and bibliography of conifers. Kew, UK: The Royal Botanical Gardens.
Furniss MM, 1967. Nematode parasites of the Douglas-fir beetle in Idaho and Utah. Journal of Economic Entomology, 60: 1323-1326.
Furniss MM, 1968. Notes on the biology and effectiveness of Kapinskiella paraomicobia parasitizing adults of Dendroconus pseudotsugae. Annals of the Entomological Society of America, 61: 1384-1389.
Furniss MM, Orr PW, 1978. Douglas-fir beetle. USDA Forest Service, Forest Insect and Disease Leaflet 5.
Furniss RL, Carolin VM, 1977. Western Forest Insects. Washington DC, USA: US Department of Agriculture Forest Service, Miscellaneous Publication No. 1339.
Massey CL, 1966. The genus Mikoletskya (Nematoda) in the United States. Helminthological Society of Washington Proceedings, 33:13-19.
Massey CL, 1967. Nematodes associated with tree infesting insects: Paurondontidae new family and Misticiinae new subfamily with a description of one new genus and four new species. Canadian Journal of Zoology, 45: 779-786.
Massey CL, 1969. New species of tylenchs associated with bark beetles in New Mexico and Colorado. Report from the Proceedings of the Helminthological Society of Washington, 36(1):43-52.
Ollieu MM, Ciesla WM, Drake LE, Mason GN, 1968. Forest pest detection survey of the mountain forests of west Texas. USDA Forest Service, Southeastern Area, State and Private Forestry, Division of Forest Pest Control, Report 69-2-25.
Sun J, Gillette NE, Miao Z, Kang L, Zhang Z, Owen DR, Stein JD, 2003. Verbenone interrupts attraction to host volatiles and reduces attack on Pinus tabuliformis (Pinaceae) by Dendroctonus valens (Coleoptera: Scolytidae) in the People's Republic of China. Canadian Entomologist, 135(5):721-732.
Weiser J, 1970. Three new pathogens of the Douglas fir beetle, Dendroctonus pseudotsugae: Nosema dendroctoni n. sp., Ophryocystis dendroctoni n. sp., and Chytridiopsis typographi n. comb. Journal of Invertebrate Pathology, 16(3):436-441
Wood SL, 1963. A revision of the bark beetle genus Dendroctonus Erichson (Coleoptera: Scolytidae). The Great Basin Naturalist, 23:1-117.
Distribution MapsTop of page
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