Douglas-fir Beetle

Dendroctonus pseudotsugae

Douglas-fir boring dust DNRC

Host: Douglas-fir trees, can also develop offspring in downed larch.

Distribution: Found throughout range of Douglas-fir. Current population levels generally declining throughout western Montana.

Identification: Look for reddish-brown boring dust accumulating in bark crevices; distinctive galleries apparent under bark layer; tree crown rapidly fading crown to bright red.

Damage: Beetles feed in phloem and introduce blue-staining fungi which, in combination, girdle the tree.

Douglas-fir beetle outbreak A. Munson

Management

Silvicultural manipulations: Douglas-fir beetle preferentially attack stressed, declining trees of compromised vigor along with mature, decadent trees. Selectively thinning the oldest and largest trees can reduce the susceptibility of the stand. Generally thinning stands to reduce competition for light, nutrients, and water will enhance the vigor of residual trees and consequently promote resilience to beetle activity. Promoting tree species that do not host Douglas-fir beetle (such as ponderosa pine and western larch) will also minimize stand-level tree mortality.

Douglas-fir beetle gallery K. Gibson	Douglas-fir beetle galleries Forestry Images

Brood trees: Identifying and removing trees currently infested with Douglas-fir beetle offspring can directly reduce populations in the stand. Accurate identification is critical for this tactic to be successful. Infested trees will commonly have an apparently healthy, green crown. Closer inspection will reveal boring dust in bark crevices and galleries under the bark. Initial attacks usually occur around 15 feet up on the bole and fill in above and below. If attacks are present in the lower bole, distinctive galleries under the bark will be present. Look for larvae, pupae, or adults under the bark to determine current infestation. Brood trees must be removed from the stand as immature beetles can successfully continue development in a cut tree. Once a tree has faded and turned red, the brood has flown and the tree is no longer a source of future infestations.

Windthrow: Douglas-fir beetle are particularly attracted to windthrown trees. Removing windthrown trees prior to beetle flight (mid-April through early June) will inhibit beetle attack and reproduction in available material. Windthrown trees can also be left on site to attract beetles and can be effectively used as "trap trees" (see below).

Douglas-fir adult beetle Forestry Images

Trap trees: Douglas-fir beetle are preferentially attracted to freshly downed material and therefore, populations can be manipulated using recently cut or windthrown trees. Large trees (greater than 15 inch diameter) should be cut in the early spring and piled in groups of 3-5 in the shade with limbs intact. These trap trees will draw beetles from the surrounding stand. Trap trees must be removed from the site prior to the following spring when the next generation disperses to new trees!

Log decks: Douglas-fir beetle will continue to develop in trees even after they are cut. Therefore, it is critical to remove infested logs from the site well before the next beetle flight period (mid-april through early June) in order to inhibit dispersal. Log decks can also attract Douglas-fir beetle and must be removed from the site prior to the next flight period. Because logging decks can attract Douglas-fir beetle, they can be used as trap trees as a means of reducing beetles in the area (see above).

Pheromones: Douglas-fir beetle communicate via chemical messages, called pheromones, and can recruit other beetles by emitting a specific aggregation pheromone. As the tree becomes too full to sustain more beetles, they switch to an anti-aggregation pheromone, essentially sending a “no vacancy” message to new arrivals. This chemical has been commercially synthesized and can be used to protect individual trees from attack.

MCH Capsule DNRC	MCH Capsule DNRC

Douglas-fir Beetle Links
Forest Insect and Disease Leaflet (FIDL)		Field Guide - Identification		Management Guide
More Information on MCH

Additional Common Forest Insects in Montana

Douglas-fir Beetle	Red Turpentine Beetle
Douglas-fir Tussock Moth	Spruce Beetle
Fir Engraver	Western Pine Beetle
Mountain Pine Beetle	Western Spruce Budworm
Engraver Beetles (Ips species)

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