Cold-hardiness of adult and larval spruce beetles Dendroctonus rufipennis (Kirby) in interior Alaska
Dendroctonus rufipennis, a serious insect pest causing periodic widespread damage to mature white spruce (Picea glauca (Moench) Voss) stands in Alaska, was studied to determine if either larvae or adults were freezing-tolerant. Mean supercooling points in both larvae and adults dropped from −12 °C in summer to about −31 °C in winter. The decrease in supercooling points in larvae was closely associated with synthesis of glycerol, but the decline in adult supercooling points partially preceded the synthesis of glycerol in the fall. Winter glycerol levels reached 3 molal. Neither larvae nor adults were freezing-tolerant at any time of the year. Measurement of temperatures beneath the bark of standing spruce showed that only beetles hibernating below the snowline would be expected to survive a typical winter.