Development and survival of the spruce bark beetle, Ips typographus (Coleoptera: Curculionidae: Scolytinae) at low temperatures in the laboratory and the field

The European spruce bark beetle (Ips typographus) is a highly destructive pest of spruce monocultures. Adult spruce bark beetles are well-adapted to survive over winter however, the ability of sub-adult stages to overwinter has not been clearly established. The increase in average temperature recorded over the last three decades has resulted in an increase in voltinism by one generation, but due to insufficient time the last generation may not complete its development. It is crucial to investigate the survival and development of sub-adult stages at low temperatures in order to predict the effect of increased voltinism on the population dynamics of this species. We measured the development and survival of larvae and pupae (over 12 weeks) in logs kept at winter temperatures outdoors (in shade and exposed to sunlight) and in the laboratory (at 0 and 5 degrees C), with 10 degrees C as a control, at which normal development was expected. Overall, findings revealed that development continued at low temperatures, although it was slower than at high temperatures. Importantly, after 12 weeks significant numbers of spruce bark beetles were present, including newly emerged adults. We demonstrate, for the first time, that sub-adult spruce bark beetles can mature over winter and the percentage survival was significant, indicating that some of the beetles that did not complete their development before the onset of winter can complete their development during winter and potentially adversely affect forests and pose problems for their management.