Inbreeding depression and its effect on intrinsic population dynamics in engraver beetles

1. Phloem‐feeding bark beetles (Coleoptera: Curculionidae, Scolytinae) generally disperse before mating, leading to expectations of outbreeding. New York and British Columbia populations of engraver beetles ( Ips pini ) were tested for inbreeding depression using different methods. Among several traits measured, only the number of offspring surviving to adulthood was strongly reduced by inbreeding. 2. There was no evidence of avoidance of inbreeding depression in two possible mechanisms considered: differential male and female emergence times within full sib broods, and early termination of brood construction in forced sib mating. 3. Sib‐mated females lay more eggs and have longer galleries than those in outbred crosses, despite a low rate of survival to adulthood for such eggs. This difference may be due to the ability of engraver beetles to assess crowding in broods as larvae begin to feed, and allows partial compensation for the effects of inbreed depression. 4. Population models assuming density‐dependent generational effects were modified to account for inbreeding depression. Inbreeding depression makes populations less prone to cyclical behaviour, particularly at lower carrying capacities. 5. Inbreeding depression has not been previously measured in scolytids, nor has inbreeding‐related behaviour been explicitly considered outside of exclusively inbreeding tribes.