The influence of host plant on the susceptibility of the fall armyworm (FAW),Spodoptera frugiperda(J. E. Smith), to a nuclear polyhedrosis virus (NPV) was investigated. Median lethal concentrations (LC50's) of NPV were determined in third-instar FAW by a leaf-disk feeding bioassay. LC50's for FAW on signalgrass/corn (88 polyhedral inclusion bodies [PIB] per mm2), corn (l05 PIB per mm2), brown-top millet (111 PIB per mm2), and signalgrass (142 PIB per mm2) were significantly higher than the LC50's for FAW on soybeans (13 PIB per mm2), bermudagrass (17 PIB per mm2), ryegrass (24 PIB per mm2), and sorghum (32 PIB per mm2), based on the lack of overlap of the 95% FL.