Field surveys and field-cage studies were conducted to evaluate the parasitoid Microplitis croceipes (Cresson) as a biological control candidate for release against corn earworm, Helicoverpa zea (Boddie), in Virginia soybeans, and to gain knowledge of its diapause behavior. Of 609 H. zea collected from corn, only one was parasitized (by Campoletis sp.) indicating that field corn is not an early-season reservoir for H. zea parasitoids. Incidence of natural M. croceipes parasitism of H. zea in soybean also was very low (only 10 of 717 larvae collected were parasitized). In total, 1,960 laboratory-reared and 1,060 field-collected H. zea larvae were released with laboratory-reared M. croceipes adult females into field cages weekly from August to October in 1990 and 1991. An average of 65% (1,975) of H. zea larvae (over all cage releases) were recovered. Of these, 990 (50%) were parasitized by M. croceipes. M. croceipes effectively parasitized wild H. zea as efficiently as laboratory-reared hosts.