Spruce beetle, Dendroctonus rufipennis
 

Fig. 64   Woodpecker bark scaling of an attacked tree.	Fig. 65  Adult spruce beetle.	Fig. 66   Trees fade to yellowish-green and then grey within a year following an attack.
Fig. 67,  Egg and larval galleries are up to 13 cm long. Frass is usually present in the galleries.	Fig. 68  Larvae. Note the anal shields.

Distribution:  Throughout the range of spruce.

Tree Species Attacked: Large-diameter, mature spruce species are attacked, including Engelmann, white, Sitka and, rarely, black spruce.

Insect Description & Damage Symptoms: The spruce beetle usually has a two-year life cycle although a one-year cycle can occur in some areas. Where this occurs, it can result in the doubling of beetle flight numbers. The larvae feed in the phloem, usually gregariously, often forming fan-shaped galleries. Two anal shields are present on the larvae, which occur on only one other Dendroctonus species, the lodgepole pine beetle. Adults are hard, stout-bodied, cylindrical insects, ranging in length from 4 to 7 mm. They are black-brown or black with reddish wing covers. Spruce beetles must overwinter once to fully mature. Mature adults emerge and attack fresh host material from late May to early July. Some immature adults may emerge in the fall to overwinter at the base of the tree.

Adults construct long galleries in the phloem. Light brown to red-brown boring dust will be present on the bark or around the base of infested trees. Pitch tubes are rarely formed by resin flowing out of the entrance holes made by attacking beetles. Sometimes flaking of the bark by woodpeckers is a sign of infestation. Fading of the foliage to a yellowish-green is usually not noticeable until 18 months or longer following attack, particularly on rich sites. By the second autumn, most of the needles have usually turned brown and are shed by the following spring. Green needles on the ground or on the leaves of ground cover beneath infested trees may appear before any evidence is visible in the crown itself.

Damage: Spruce beetles normally infest downed trees or logging debris, but when beetle populations are large, they will attack and kill living trees, causing widespread damage. Trees are killed when the flow of food and water between the roots and needles is blocked by a combination of feeding larvae and dead sapwood cells killed by the blue-stain fungi carried by the spruce beetle adults.

Similar Damage: Attacks by secondary bark beetles may produce boring dust in bark crevices. Ips beetle species can be distinguished by the gallery patterns and the lack of frass in galleries. The adult ips beetle differs from the spruce beetle in that it has a rear concave depression lined with spines. Spruce beetle larvae can be distinguished from most other Dendroctonus species by the presence of two anal shields.

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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