Spruce Beetle

Spruce beetle feed on the inner bark of white, Lutz, Sitka and black spruce. This mining of inner bark by larvae usually kills trees within one or two years. The crowns of trees girdled by beetles in one year usually turn red and die by the following year. Spruce beetle is a serious forest pest in south-central Alaska (approximately 140 to 155 degrees longitude) throughout Cook Inlet and Kenai Peninsula. Many trees can also be killed in southeast Alaska (approximately 130 to 139 degrees longitude) but outbreaks are usually of shorter duration and cover only a fraction of the acreage that is infested in south-central Alaska. In 1996, southeast Alaska, there were ongoing outbreaks near the town of Haines, on Excursion Ridge, along the Taku and Stikine rivers, and on Dall Island. The earliest recorded outbreak in the 1920's covered 200,000 acres. Approximately 500,000 acres were infested in the late 1970's. Beginning about 1988 the current epidemic has been bigger than ever recorded with over 1,000,000 acres of trees currently infested.

Female beetles initiate attacks in spring (late May or June) and begin constructing an egg gallery in the cambium parallel to the grain of the tree. They lay eggs in small niches along the sides of the egg gallery. Most eggs will hatch by August. Larvae construct their own galleries perpendicular to the egg gallery. Normally, spruce beetles pass the first winter in the larval stage, resume feeding the next spring, and pupate by summer. About two weeks later, pupae transform into adults which pass the second winter, either in the old pupation site, or more commonly, in the bases of infested trees. The following spring, two years after initial attack, the new adults emerge and attack new trees. In some years when temperatures are abnormally high, spruce beetles may complete their development within one season.

Natural controls have been regulating factors in spruce beetle epidemics. Most major outbreaks originate from stand disturbances that result in substantial accumulations of down, green, large diameter (> 8") spruce (e.g. blowdown, logging, or right of way clearance). Stand susceptibility to beetle attack is influenced by stocking, with slow growth and moisture stress playing an important part in predisposing trees to attack. Forest management activities that remove infested logs and increase the vigor of spruce will help to contain or minimize the effects of epidemics. The use of spruce beetle pheromones may help to direct attacks away from valuable trees.

Adult spruce beetles are maroon to black, cylindrical in shape, approximately 5 mm long and 3 mm wide. Larvae are stout, white, legless grubs, 6 mm long when full grown. The pupae are soft bodied, white, and have some adult features.

REFERENCES:
Eglitis, A. 1988. Spruce Beetle in the Glacier Bay National Park: 1987 Update. USDA. Forest Service, Alaska Region. Biological Evaluation R10-89-1. 13 p.

Holsten, E.H. 1990. Spruce beetle activity in Alaska: 1920-1989. USDA Forest Service, Alaska Region Technical Report R10-90-18. 28 p.

Holsten, E.H., Their, R.W. and J.M. Schmid. 1991. The spruce beetle. USDA Forest Service. Forest Insect and Disease Leaflet 127. 12 p.

Humphreys, H. and L. Safranyik. 1993. Spruce beetle. Forestry Canada. Pacific Forestry Centre. Forest Pest Leaflet 13. 7 p.

Schultz, M.E. 1996. Dall Island Sitka Spruce Mortality Survey - 1996. USDA Forest Service, Alaska Region. Technical Report R10-TP-63. 14 p.