The biology of Crymodes devastator [Apaniea devastatrix], a subterranean pest of grasses grown for seed, was studied in the laboratory at 20'C and LD 16:8 and in the field in Oregon. Light trap captures indicated that adult flight occurred from July to September, peaking in late July. Postharvest field burning eliminated all foliage and crop residue, probably making fields temporarily unsuitable for oviposition. Bentgrass (Agrostis tenuis [A. capillaris]), ryegrass (Lolium perenne and L. mulliflorum) and wild oats (Avena fatua), occurring as weeds in fine fescue [Festuca sp.] fields, attracted ovipositing females. High densities of feeding larvae damaged or killed the crop near weeds and became evident in late autumn. Larvae 1.5- 2 cm in length were present in fields during winter and readily began feeding after exposure to 21 'C for 2-7 days in the laboratory. The tachinid Nowickia latianulum [Tachina latianulum] and the ichneumonid Lissonota montana collectively parasitized 30 and 48% of larvae collected from 2 sites. none