Fall armyworm, Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae), is composed of two sympatric, morphologically identical host strains (corn and rice) that differ in their distribution on different host plants. This suggests possible strain specificity in the use of host plants. However, although feeding studies published since 1987 have reported such developmental differences, the results were often contradictory, making generalizations about strain-specific physiological traits problematic. Here, we tested whether more consistent results could be obtained using several genetically characterized colonies when assayed in the same laboratory. We also assessed whether a commonly used meridic diet was more favorable to one strain and the potential this might have on altering the behavior of artificially raised colonies. Corn and rice strain colonies were characterized by cytochrome oxidase I (COI) strain markers and were subjected to feeding studies using corn (Zea mays L.), stargrass (Cynodon nlemfuensis Vanderyst variety nlemfuensis ‘Florona’), and a meridic pinto bean diet. In 2005 bioassays, all colonies developed best on corn, whereas the meridic and stargrass diets were associated with more pronounced strain differences. However, bioassays conducted in 2010 using different colonies showed fewer differences between host strains. The limitations of feeding bioassays and the COI marker to identify host strains and the potential for unintended selection of corn strain traits when using a meridic diet are discussed.