Individual females ofTrichogramma nubilaleErtle and Davis were exposed to various densities (1 to 12) of European corn borer (ECB),ostrinia nubilalis(Hübner), egg masses for different exposure periods (l to 120 h). This parasitoid avoided excessive superparasitism under every host density and exposure period tested. It appears that the ovipositional behavior and manner of progeny distribution ofT. nubilalefemales are uniquely adapted to the mode of egg laying by its natural host, the ECB.