I studied the diurnal and ontological patterns of feeding by European corn borer adults, Ostrinia nubilalis (Hübner), and characterized the effect of feeding on adult mortality in the laboratory. Adults were provided a sucrose diet and water ad libitum, and were observed at periodic intervals to estimate the proportion feeding on sucrose or water. Dead adults were counted daily to estimate mortality. Adults preferred to feed on the sucrose diet during the first week of life, but not thereafter. Feeding occurred mainly just after the lights were turned off but also just after lights were turned on, and this time preference also waned by the second week of life. Daily mortality rates increased during adult life. These results are consistent with other studies on adult mortality, and suggest that feeding on sugar may be beneficial for adults only when their life expectancy exceeds 4 d.