Studies were conducted at eight locations in Ingham County, Michigan, during 1989–1990 to determine the within-field distribution of European corn borer,Ostrinia nubilalis(H¨bner), larval parasitism.O. nubilalislarval sampling was conducted at multiple locations on three transects across large 1st-yr corn fields during the F1and F2generations. Plants were destructively sampled to determineO. nubilalisabundance and larvae were returned to the lab to determine parasitism.Eriborus terebrans(Gravenhorst) (Hymenoptera: Ichneumonidae) was the dominant parasitoid ofO. nubilalisin the sampled fields, accounting for 92.5% of the F1and 99.2% of the F2parasitism during 1989; and for 92.2% of the F1and 99.1% of the F2during 1990. Average parasitism byE. terebrans(n= 4 fields) was 4.9 and 18.7% of F1, 10.2 and 9.1% of F2larvae during 1989 and 1990 respectively. The maximumE. terebransparasitism observed (37.4%) of theO. nubilalislarvae in one field (F11990), is the highest level reported for this species in the Midwest. Parasitism byE. terebransduring the F1generation was greater along field margins than in field interiors in most fields during both years. During 1990,O. nubilalislarvae near wooded edges had significantly higherE. terebransparasitism than those near nonwooded edges or field interiors. In the F2generation, parasitism did not vary significantly from field margins to field interiors in either year. There was no consistent relationship betweenO. nubilalislarval density per infested plant andE. terebransparasitism. These data suggest that local landscape structure, including proximity of particular noncrop habitats, plays an important role in the effectiveness of this natural enemy.