Releases of 835 mated adult femaleCampoletis sonorensis(Cameron) at a rate of 50–100/day for 10 days against an introduced population of tobacco budworms,Heliothis virescens(F.), on cotton in a 0.4-acre field cage resulted in 85–95% parasitization of tobacco budworm larvae for ca. 2 months. As host pressure was maintained by daily releases of adult moths,C. sonorensiswas eventually replaced as the major regulator of the tobacco budworm population by parasitization of host eggs byTrichogrammasp. and predation of host eggs and small larvae byOrius insidiosus(Say). TheC. sonorensispopulation was also greatly affected by the hyperparasitesCatolaccus aeneoviridis(Girault) andCeratosmicra immaculata(Cresson); and the predatorCollops vittatus(Say) consumed up to 70% of the cocoons ofC. sonorensis. Nevertheless, the beneficial species markedly suppressed the tobacco budworm population throughout the experiment. Weekly average temperatures between 80 and 86°F did not appear to reduce the efficiency ofC. sonorensis. The sex ratio of parasites produced in a field cage was near 1:1 as compared to 1:4 in a culture maintained in the laboratory.