Establishment and spread of two introduced parasitoids (Ichneumonidae) of the birch leafminer, Fenusa pusilla (Lepeletier) (Tenthredinidae)

Lathrolestes nigricollis (Thomson) and Grypocentrus albipes Ruthe, Palearct ic specialist parasitoids of the birch-leafmining sawfly Fenusa pusilla (Le peletier), were imported from central Europe and released at three location s in Edmonton, Alberta, Canada during 1994-1996. Parasitoids became establi shed at two locations, L. nigricollis at both and G. albipes at one, and we re recovered for 3-5 years after release. Lathrolestes nigricollis has disp ersed throughout most of Edmonton, and at least 13 km from release sites, b ut G. albipes has been recovered only 400-500 m from one release site. Five years after introduction at one site, percent parasitism by L. nigricollis was 78% and 84% for the first and second generations, respectively, and ab out 48% of parasitoid eggs were encapsulated.