none European corn borer larvae, Ostrinia nubilalis (Hubner) (Lepidoptera: Crambidae) that have completed development on Event 176 Bt corn hybrids have survived exposure to sublethal doses of the Cry1Ab Bt toxin or are exploiting plant tissues that do not express the toxin. To evaluate the impact of such exposure, diapausing larvae were collected from Event 176 and conventional hybrids and compared for rates of pupation, parasitism, fitness (pupal weight, longevity, and fecundity) and susceptibility to the Cry1Ab toxin. Larvae completing development on Event 176 corn exhibited approximately 10% higher survival rates and correspondingly lower parasitism rates than larvae completing development on conventional hybrids. No significant differences were detected in pupal weight, fecundity, longevity or susceptibility to the Cry1Ab Bt toxin. These results indicate that survival on Event 176 corn are not adversely affect fitness and does not cause increased tolerance to the Cry1Ab toxin in subsequent generations. Animals and man; Control; Biometrics; Nutrition; Diet; Reproduction; Reproductive productivity; Life cycle and development; Development; Evolution; Parasites diseases and disorders; Parasites; Insect parasites; Hosts; Insect hosts; Ecology; Population dynamics Ostrinia nubilalis (Pyralidae); Biological control; Transgenic food plants expressing bacterial toxin; Weight; Food plants; Maize; Larval development on transgenic plants expressing bacterial toxin, effects on survival & fitness; Fecundity; Longevity; Natural selection; Fitness; Hymenopteran parasites; Eriborus terebrans & Macrocentrus grandii; Survival Macrocentrus grandii (Braconidae ); Eriborus terebrans (Ichneumonidae ); Lepidopteran hosts; Ostrinia nubilalis; Prevalence rates, effects of host rearing on transgenic food plants