SPRUCE BEETLE

N. Humphreys and L. Safranyik

Introduction

The spruce beetle, Dendroctonus rufipennis, is the most destructive pest of mature spruce trees in British Columbia. Outbreaks usually last 2-5 years, and these may severely deplete the large-diameter spruce (Picea spp.) component of forest stands.

In the 1940s, an outbreak of this native insect in northwestern British Columbia and southwestern Yukon occurred over 375 km 2 . Up to 90% of the spruce trees were killed and timber loss-es were estimated at 878 000 m 3 . Another infestation during the same period occurred over 777 km 2 in the upper Nass River Valley. During 1952- 1956, 400 000 m 3 of spruce were killed in southeastern British Columbia. At the same time, a much more extensive out-break was in progress in northern Idaho and western Montana. From 1961 to 1965, an epidemic affecting over 243 000 ha in the Prince George and Prince Rupert Forest Regions caused losses of over 14 million m 3 . The attack in 1962 accounted for more than half of the total volume killed. In 1967 and 1968, outbreaks in the Prince George Forest Region again occurred over extensive areas, killing 822 000 m 3 of spruce. Extensive tree mortality also occurred in the Nelson and Cariboo Forest Regions from 1967 to 1971, and sever-al large infestations that began in 1969 continued in the Kamloops Forest District until 1973.

Since the early 1970s, further out-breaks of the beetle have occurred across the province, often associated with windthrown spruce, or with poor forest sanitation practices. For exam-ple, significant increases in population levels and attack occurred during 1978-1982 in the Prince George Forest Region. Over 60 000 ha were attacked in the Willow, Bowron, McGregor, and several other river drainages. By 1982, trees amounting to over 2 million m 3 of wood volume had been killed. This prompted the forest industry to undertake several large-scale salvage operations.

Spruce beetle populations declined during the mid to late 1980s, but occasional local outbreaks were recorded throughout the province. In 1987, most of the 1675 ha of infested spruce recorded were located in the Kamloops and Nelson Forest Regions. A resurgence of spruce beetle attack was recorded during 1990 and 1991, again primarily in the Prince George Forest Region. Across the region, aerial surveys indicated that infestations were scattered over more than 44 000 ha. Current stud-ies suggest the threat to mature and healthy spruce will continue, particu-larly in stands north of Mackenzie and west of Williston Lake after 2-year cycle broods mature in 1993.

Severe losses to the spruce bee-tle in any one year can equal or exceed 10% of the volume of spruce harvested in British Columbia; this is cause for concern among all resource managers, not just foresters. Attacks in parks or ecological reserves, for example, can seriously affect aesthet-ic, recreational, and scientific values, as well as timber values.

For more information, see the SPRUCE BEETLE Forest Pest Leaflet in the Canadian Forest Service bookstore.

Archived Content

SPRUCE BEETLE

Introduction