Factors Influencing Generation Times of Spruce Beetles in Alaska
Canadian Journal of Forest Research
The influence of stand aspect, tree position in relation to direct solar radiation, cumulative degree-day temp., and phloem temp., m.c. and thickness on development, survival and attack of Dendroctonus rufipennis was measured in standing and felled white spruce trees in stands in the Chugach National Forest. Direct solar radiation to the bark surface was the primary environmental factor influencing the developmental rate of spruce beetles. A phloem threshold temp. of 16.5C was required to initiate the development of 1-yr life cycle beetles. Tree location within a stand and stand aspect in relation to direct solar radiation determined which trees or areas of the tree supported beetles with 1- and 2-yr life cycles. Two-yr cycles normally developed on the north and west sides of standing trees and the north and bottom sites of felled trees, which were characterized by an av. phloem temp. of 10.6C. One-yr cycles normally developed on the south sides of standing trees and the south and top sides of felled trees, which were characterized by an av. phloem temp. of 16.5C. Attacks were greatest at the base (rather than the mid or top) of standing trees, and on the south and east of felled trees. Survival was highest at the base and lowest at the top of standing and felled trees.
Werner, R. and Holsten, E. (1985). Factors influencing generation times of spruce beetles in Alaska. Can. J. For. Res. 15(2): 438–443.