Larvae of the black spruce cone maggot, Strobilomyia appalachensis, were infected and killed by Steinernema carpocapsae (Weiser) All and Umeå strains, S. feltiae (Filipjev) (= bibionis) strain 27, and S. glaseri Steiner strain 326, in laboratory tests. After formation of puparia, however, cone maggots were practically resistant to all species and strains tested. Very few or no maggots were infected when nematodes were sprayed on or injected into infested spruce cones. The survival, activity, and infectivity of infective juveniles held in an aerated infusion of black spruce cones were significantly lower compared with those held in aerated water. In peat–sand columns, the proportion of larvae infected with S. feltiae, but not S. carpocapsae Umeå strain, was significantly greater when larvae were dropped immediately or 1 day following nematode application compared with 1 day before or 3 days following nematode application. Our results suggest that, in field trials for cone maggot suppression, nematodes should be applied within a day prior to larval drop and that repeated applications may be required for persistence of sufficient infectivity.