Reproduction and developmental phenology of IPS perturbatus (Coleoptera: Scolytidae) inhabiting white spruce (Pinaceae)

Three white spruces, Picea glauca (Moench) Voss (30-35 cm diameter at breast height), felled in central Alberta, were colonized by Ips perturbatus (Eichhoff) beginning in late May 1999. The mean (±SE) density of breeding galleries on the trees was 217 ± 23/m² (n = 30). Harem size ranged from one to four females per gallery, with a mean of 2.1 ± 0.6 (n = 90). Tunnel excavation and oviposition occured primarily during the first 3 weeks after gallery initiation. Individual females laid 48.9 ± 2.5 eggs (n = 30) in galleries that reached 10.0 ± 0.3 cm in length (n = 45). Males assisted their mates by removing frass and woody debris from the tunnels. Males remained in their galleries for at least 1 week, although there was gradual attrition such that < 15% of males remained after 6 weeks. Large males abandoned their galleries sooner than small males. In contrast, females were present in almost half of the oviposition tunnels examined after 6 weeks, and there was no significant relationship between female size and residence time. Mortality from egg to adult was high (98%) during this 1-year study, likely a result of the intense crowding of galleries. Adult offspring were found beneath the bark in mid-July, although the main emergence did not begin until mid-September. Because such late emergence would be too late for these individuals to reproduce before winter, I conclude that I. perturbatus has only one generation per year in central Alberta.