The Holarctic ichneumonid parasitoid Lathrolestes luteolator (Gravenhorst) was found attacking Profenusa thomsoni (Konow), an introduced birch-leafmining sawfly, in Edmonton, Alberta. This appears to be a recently evolved host-parasitoid association in Alberta. Populations of L. luteolator increased dramatically relative to those of P. thomsoni as the sawfly declined from epidemic to low levels between 1992 and 1995, after a sustained outbreak beginning with its earliest local detection in the early 1970s. The only previously recorded host of L. luteolator that occurs in Alberta is the tenthredinid Caliroa cerasi L.; however, L. luteolator was not associated with a population of C. cerasi sampled during 1995. Sampling at several locations in Alberta, Saskatchewan, and Ontario showed that L. luteolator is currently associated with populations of P. thomsoni throughout Canada. Further study is required to determine whether L. luteolator is involved in regulating populations of P. thomsoni at the present low levels observed in central Alberta. none