Distributions of leafmining sawflies (Hymenoptera: Tenthredinidae) on birch and alder in northwestern Canada

Exotic leafmining sawflies (Hymenoptera: Tenthredinidae) on birch (Betula spp., Betulaceae) have become widely distributed in Canada since their introduction to eastern North America in the last century (Digweed et al. 1997). However, their distributions north of the 60th parallel are poorly known (Digweed et al. 2003). No birch leafmining sawflies were detected at Hay River and Louise Falls, Northwest Territories (NT), in 1993, but the ambermarked birch leafminer, Profenusa thomsoni (Konow), was reported from Yellowknife, NT, in 1994 (Digweed et al. 1997). Since that time, P. thomsoni populations have reached epidemic levels on urban birches in Yellowknife and Hay River, NT (unpublished data). While examining infested birches in Hay River in 2003, the authors also found the European alder leafminer, Fenusa dohrnii (Tischbein), attacking alder (Alnus spp., Betulaceae).