Douglas-fir beetle, Dendroctonus pseudotsugae
 

Fig. 69   Larva in gallery.	Fig. 70  Adult Douglas-fir beetle.	Fig. 71   Egg and larval galleries are about 30 cm in length and packed with frass.
Fig. 72,  Attacked trees. Note: red colour usually appears by the spring of the year following an attack.	Fig. 73  Boring dust can be found in crevices at the base of the tree.

Distribution:  Throughout most of the range of its principal host.  Damage is usually most intensive in the interior of B.C. 

Tree Species Attacked: Large-diameter, mature Douglas-fir trees are attacked, and occasionally, downed western larch.

Insect Description & Damage Symptoms: Adults are dark brown to black with reddish wing covers and about 4.4 to 7 mm long. The usual life cycle is one year, but two broods may be produced. The main flight period usually occurs in May and June, while a second flight in July and August may be made by adults developed from overwintering larvae or adults re-emerging after the earlier flight.

Adults lay their eggs in long galleries constructed parallel to the grain of inner bark. Reddish boring dust may be found in bark crevices or at the base of the tree. Adult beetles will often not attack the bottom portion of the bole, making identification difficult. Pitch tubes are not formed, but the tree may exude resin from upper attacks. Foliage of killed trees turns from green to pale yellow-green to red by the spring of the year following the attack. Red needles may remain on the tree for up to two years after an attack and aerial spotting of these "redtops" helps to determine the extent of an outbreak. Sometimes needles will drop without any discolouration.

Damage: Douglas-fir beetles normally infest felled trees, mature damaged trees, logging debris, and trees stressed by drought. When sufficient host material is unavailable, however, they will attack and kill vigorous trees, causing more extensive damage. Trees are killed when the flow of food and water between the roots and needles is blocked by feeding larvae and by dead sapwood cells killed by the blue-stain fungi carried by the Douglas-fir beetle adults. On the coast, it often takes two years of attack to kill a tree (partial or "strip" attack occurs the first year).

Similar Damage: Attacks by secondary bark beetles may produce boring dust in bark crevices. The Douglas-fir pole beetle is usually found in the smaller diameter, upper portion of the stem. It can be distinguished from the Douglas-fir beetle by its finer boring dust and different gallery patterns.

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BC Ministry of Forests
Forest Practices Branch
P.O. Box 9513 Stn. Prov. Gov.
Victoria, BC
V8W 9C2

Section phone: (250) 387-8739
Section fax: (250) 387-2136

Last updated March 12, 2002