Ergot alkaloids produced by endophytic fungi in the tribe Balansiae (Clavicipitaceae, Ascomycetes), which infect grasses, may provide plant defense against herbivores. This study examined the effects of six ergot alkaloids on survivorship, feeding, and growth of larvae of the fall armyworm (Spodoptera frugiperda, Lepidoptera: Noctuidae), a generalist herbivore of grasses. Corn leaf disks were soaked in solutions of individual ergot alkaloids at different concentrations and presented to neonate larvae. At the highest concentrations (77-100 mg/liter) of ergonovine, ergotamine, ergocryptine, agroclavine, and elymoclavine, larval weights and/or leaf area consumed after eight days were reduced relative to controls. Lysergol had no effect on larval weights and leaf consumption at any concentration. Although active concentrations were higher than those reported from two host grasses, in vivo levels of ergot alkaloids have not been quantified for most endophyte-infected grasses. The detrimental effects on fall armyworm observed in this study suggest that ergot alkaloids could be responsible, at least in part, for the greater insect resistance of endophyte-infected grasses.