Heliothis zea(Boddie) larvae and eggs were collected from soybean fields in five Virginia counties during 1987 and six counties in 1988.Microplitis croceipes(Cresson) was the predominant parasitoid associated withH. zealarvae throughout the study. GreaterH. zealarval density and rates of parasitism were observed in fields planted after 10 June than in fields that were planted earlier. High levels of parasitism occurred only in fields where the presence ofM. croceipescoincided with first appearance of host larvae. Most parasitoids emerged fromH. zealarvae collected as third or fourth instars. No parasitoids emerged fromH. zealarvae sampled from field corn, suggesting thatM. croceipespopulations in soybeans do not originate fromH. zeahosts in corn fields. Despite warm holding temperature, 14% of theM. croceipesprepupae collected in 1987 entered diapause in the laboratory and emerged in August the following year. This is evidence for the hypothesis thatM. croceipesoverwinter in soybean fields and emerge in summer to coincide with first presence ofH. zealarvae. Less than 4% of collectedH. zeaeggs were parasitized by Trichogrammatidae in Eastern Shore counties. However, high levelsof egg parasitism,>90% on some sample dates, occurred in fields in the Northern Neck.