Factors influencing generation times of spruce beetles in Alaska

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Abstract
Direct solar radiation to the bark surface of white spruce, Picea glauca (Moench) Voss, is the primary environmental factor influencing the developmental rate of spruce beetles, D. rufipennis (Kirby), in Alaska. A phloem threshold temperature of 16.5.degree. C is 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 determine which trees or areas of the tree support beetles with 1- and 2-yr life cycles. Two-year cycles normally developed on the north and west sides of standing trees and the north and bottom sides of felled trees, which were characterized by an average phloem temperature of 10.6.degree. C. One-year cycles normally developed on the south sides of standing trees and the south and top sides of felled trees, which were characterized by an average phloem temperature of 16.5.degree. C.