Winter mortality in sub-corticolous populations of Ips typographus (Coleoptera, Scolytidae) and its parasitoids in the south-eastern Alps

A study concerning the winter mortality of a sub-corticolous population of Ips typographus and its parasitoids has been carried out in the south-eastern Alps (Italy) during the winter 1997/98. Three attacked spruce trees were sampled three times (November, February and April) by collecting infested bark disks (1 dm2 each). All insects that emerged from the bark or died in the samples before emergence were counted. The mean number of living Ips typographus occurring under the bark decreases by 49 % from November to April. Winter mortality mainly affects larval stages and young adults. The same trend was observed for the parasitoids Coeloides bostrychorum (48.5 %) and Roptrocerus xylophagorum (47.5 %).