Technical Abstract: Genetically engineered maize producing insecticidal Cry3Bb1protein from Bacillus thuringiensis (Bt) is protected from root damage by corn rootworm larvae. An examination was made to establish whether western corn rootworm (Diabrotica virgifera virgifera) adults are affected by Cry3Bb1-expressing maize (MON88017) when feeding on above-ground tissue. Effects of Bt maize on some life-table parameters, i.e., fecundity and male survival, were observed, but no consistent relationship with the level of exposure to Cry3Bb1 was present. The observed effects can be explained by direct effects of the expressed Bt protein, but also by potential variety effects between the Bt and near-isoline. Nutritional quality of different plant parts was important for adult performance, but did not seem to affect the beetle’s sensitivity to Bt maize. The results indicate that the impact of Bt maize on adult populations is likely to be limited.