During the course of an investigation carried out some years ago by the writer in the Gaspe peninsula of Quebec, it was discovered that adults of Dendroctonus piceaperda Hopk., Polygraphus rufipennis Kby., Ips perturbatus Eichh., and Ips borealis Sw., cut two sets of tunnels the same season and in some cases hibernated and cut tunnels in the following season. Subsequently, a series of detailed studies on the biology of Canadian barkbeetles has been in progress in field laboratories at Fredericton, N. B., Frater, Ont., Vernon, B.C., and Pender Harbour, B. C.