Fall armyworm, Spodoptera frugiperda (J.E. Smith), and Southwestern corn borer, Diatraea grandiosella Dyar, are economically important pests of maize (Zea mays L.) in the southeastern United States. These insects attack plants in both the vegetative and reproductive stages of growth. Plant resistance is widely considered a desirable means for reducing losses to both insects, and corn germplasm lines with resistance to leaf feeding damage have been developed and released. Fall armyworm and southwestern corn borer larvae feeding on resistant genotypes grow more slowly than those feeding on susceptible genotypes. The objectives of the investigation were to evaluate 20 single cross maize hybrids for leaf feeding damage by southwestern corn borer and fall armyworm, to compare larval growth on laboratory diets prepared from lyophilized leaf tissue of single cross hybrids with different levels of resistance to leaf feeding, and to determine whether larval growth differed between diets prepared from leaf tissue collected from plants previously infested with southwestern corn borer or fall armyworm and non-infested plants. Both fall armyworm and southwestern corn borer larvae weighed significantly less when fed on laboratory diets prepared from lyophilized leaf tissue of resistant single cross hybrids than susceptible hybrids. When tissue from either resistant or susceptible plants that had been infested with either insect in the field was used in bioassays, larval weights were further reduced. It appears that both constitutive and induced defensive mechanisms may be operating.