Forty-nine species of Carabidae were collected from 10 alfalfa fields in Rockbridge County, Va. Species composition and diversity of carabid populations were affected by insecticides applied to control the alfalfa weevil,Hypera postica(Gyllenhal) (Coleoptera: Curculionidae)Harpalus pensylvanicusDeGeer (Coleoptera: Carabidae), a species known to feed on diapausing forms of the alfalfa weevil parasite,Bathyplectes curculionis(Thomson) (Hymenoptera: Ichneumonidae), and on adult alfalfa weevils was more abundant in untreated alfalfa fields than in fields treated with insecticides. A positive relationship was found between densities of adultH. pensylvanicusand damagedBathyplectesspp. cocoons.