Microctonus melanopus (Ruthe) were reared and dissected from adult cabbage seedpod weevil, Ceutorhynchus obstrictus (Marsham), collected in southern Alberta in 2000 and 2001, and M. melanopus females were collected near Creston, British Columbia in 2001. These collections represent the first records for this European species in Canada. Previously published records of M. melanopus in North America are from the northwestern United States. A first diagnosis for adult female M. melanopus is provided that places M. melanopus in Loan's (1969) key for Microctonus species of North America, north of Mexico. Scanning electron photomicrographs of female morphology are provided to illustrate important diagnostic characters: the mesonotal sculpture with a distinct median longitudinal carina posteriorly, and the sculpture of metasomal tergite 1 with costae distinctly converging posteriorly. It is probable that M. melanopus has long been established in the southern interior of British Columbia because its host, C. obstrictus, has occurred there for many years. The occurrence of M. melanopus in southern Alberta is likely more recent, as its host only recently dispersed to that region. Rates of parasitism of C. obstrictus by M. melanopus, with one exception, were low in southern Alberta ( 10%), and only one parasitized weevil was found on spring-seeded Brassica napus L., the primary brassicaceous oilseed crop associated with the weevil on the Canadian prairies. We hypothesize that M. melanopus will not provide substantial control of C. obstrictus in the mixed grassland ecoregion of its new range. Systematics; Nomenclature; Parasites diseases and disorders; Parasites; Insect parasites; Hosts; Insect hosts; Land zones; Nearctic region; Canada; North America Ceutorhynchus obstrictus (Curculionidae); Hymenopteran parasites; Microctonus melanopus; New host record; Alberta; Lethbrdge & Nobleford; New hymenopteran host record Microctonus melanopus (Braconidae); Coleopteran hosts; Ceutorhynchus obstrictus; Alberta; Lethbrdge & Nobleford; New record, coleopteran host Microctonus melanopus (Ruthe) (Braconidae); Diagnosis; Female, p. 353 none