Dendroctonus pseudotsugae

Adults range 4.4–7 mm in length and are somewhat hairy. Coloration shifts from light brown in young adults to dark brown or black with reddish wing covers in mature individuals. Larvae are small, legless, white, and rice-grain sized. Pupae are white to cream colored. Visible infestation signs include orange to reddish-brown boring dust in bark crevices or at the tree base, resin streamers from higher attacks, and 6–30 inch egg galleries running parallel to wood grain beneath the bark. Eggs are laid on either side of the gallery; hatched larvae mine perpendicular to the galleries.

Forests dominated by Douglas-fir (Pseudotsuga menziesii) throughout western North America. Outbreaks are associated with freshly windthrown or cut trees, fire-damaged stands, root rot, overcrowding, foliar insect damage, and drought-stressed trees. The species occasionally colonizes western larch (Larix occidentalis) in proximity to Douglas-fir, though brood survival in live larch is prevented by host chemical defenses.

Western North America from Canada (British Columbia, Alberta) through the United States (Washington, Oregon, California, Idaho, Montana, Wyoming, Nevada, Utah, Colorado, Arizona, New Mexico, Texas) to Mexico.

Phloem of Douglas-fir (Pseudotsuga menziesii). Adults and larvae feed on the nutrient-conducting tissue beneath the bark.

• Pseudotsuga menziesii - primary hostDouglas-fir; sole host supporting successful reproduction in live trees
• Larix occidentalis - secondary hostWestern larch; colonized when in proximity to Douglas-fir but brood do not survive in live trees due to high 3-carene content

Eggs are laid in galleries beneath the bark of host trees. Larvae hatch and mine perpendicular to egg galleries, feeding on phloem. Pupation occurs in chambers within the bark. Adults emerge to disperse and locate new hosts. Under favorable conditions, parent females may produce sibling broods—second or third clutches laid later in the season that overwinter and complete development the following spring.

Newly emerged adults exhibit temperature and light preferences that shift with physiological state: initially photopositive and preferring temperatures near flight thresholds, becoming more photonegative and host-positive after conditioning, aging, or flight. Females initiate host colonization and produce aggregation pheromones that attract both sexes. Males stridulate and release an antiaggregation pheromone (3-methylcyclohex-2-en-1-one, or MCH) after mating, which signals tree saturation and redirects late-arriving beetles to alternative hosts. The beetle also releases limonene during stridulation-induced pheromone emission. Host selection involves initial attraction to oleoresin volatiles (α-pinene, camphene, limonene) from stressed or damaged trees, followed by stronger secondary attraction to female-produced aggregation pheromones.

Functions as a disturbance agent in western forest ecosystems, preferentially thinning weakened or stressed Douglas-fir trees. During outbreaks, population increases can lead to mass attacks that kill healthy, mature trees including remnant old-growth specimens. The species contributes to nutrient cycling through phloem consumption and wood decomposition, though outbreak-scale mortality alters stand structure and succession patterns.

Major economic pest of Douglas-fir timber resources. Outbreaks cause substantial timber loss and threaten high-value trees in campgrounds, residential areas, and special-use sites. Management relies heavily on the antiaggregation pheromone MCH (3-methylcyclohex-2-en-1-one), applied via bubble capsules to protect individual trees or stands—currently the most effective operational pheromone-based bark beetle treatment globally. Historical suppression methods included sanitation harvesting of infested material. Climate change and altered forest conditions may influence outbreak dynamics and geographic range.

• Dendroctonus frontalisSouthern pine beetle; similar bark beetle morphology and gallery construction, but restricted to eastern North American pines, smaller size, and distinct pheromone chemistry including frontalin and exo-brevicomin
• Dendroctonus simplexEastern larch beetle; attacks tamarack (Larix laricina) in northeastern North America, similar size range and life history but distinct host genus and geographic range
• Dendroctonus terebransBlack turpentine beetle; colonizes lower trunk of pines in eastern North America, larger size (5–8 mm), does not kill trees outright, and produces semiochemicals that may attract D. frontalis
• Dendroctonus brevicomisWestern pine beetle; similar western North American range and Douglas-fir host association, but distinguished by gallery pattern and pheromone components
• Ips spp.Engraver beetles; co-occur in conifer forests but have multiple spines on declivity (posterior slope of elytra), different gallery patterns (H- or I-shaped), and typically attack smaller diameter material or tree tops

• bark beetle
• forest pest
• pheromone
• Douglas-fir
• Scolytinae
• integrated pest management
• MCH
• antiaggregation pheromone
• western North America
• phloem feeder
• tree mortality
• outbreak dynamics
• semiochemicals
• limonene
• frontalin
• 3-carene
• sibling broods
• climate change
• old-growth forest
• timber protection

• BugGuide
• Wikipedia
• GBIF taxonomy match
• iNaturalist taxon
• NCBI Taxonomy
• Catalogue of Life
• The Day That The Beetles Invaded the Bohart | Bug Squad
• Publications | Entomology Research Museum
• Pheromone Treatment Puts Up the "No Vacancy" Sign for Douglas-Fir Beetles
• Southern Pine Beetle: How a Fellow Species May Help in Host Location
• Managing Southern Pine Beetle Infestations in a Changing Forest Environment
• Eastern Larch Beetle Outbreak Keeps Going When Winter's Not So Cold
• Dendroctonus pseudotsugae . [Distribution map].
• Limonene released by the Scolytid beetle Dendroctonus pseudotsugae
• Masking of the Aggregation Pheromone in Dendroctonus pseudotsugae Hopk.
• The phoretic mite (Arachnida: Acari) assemblage of the Douglas-fir beetle, Dendroctonus pseudotsugae Hopkins (Coleoptera: Curculionidae)
• Laboratory Studies on the Behaviour of the Douglas-fir Beetle,Dendroctonus pseudotsugaeHopkins
• Role of 3-Carene in Host Location and Colonization by Dendroctonus pseudotsugae (Coleoptera: Curculionidae)
• On the Flight and Host Selection of the Douglas-fir Beetle, Dendroctonus pseudotsugae Hopk. (Coleoptera: Scolytidae)
• Studies on Nervous System Anatomy of the Douglas Fir Beetle, Dendroctonus pseudotsugae Hopk. (Scolytidae)
• A Study of the Flight of the Douglas-Fir BeetleDendroctonus pseudotsugaeHopk. (Coleoptera: Scolytidae): II. Flight Movements
• Host Selection and Invasion by the Douglas-fir Beetle, Dendroctonus pseudotsugae Hopkins, in Coastal Douglas-fir Forests
• Laboratory and Field Methods for Assaying Olfactory Responses of the Douglas-fir Beetle, Dendroctonus pseudotsugae Hopkins