Fall armyworm (FAW), Spodoptera frugiperda (J. E. Smith), larvae populations were investigated in three studies, including sorghum (Sorghum bicolor (L.) Moench] in pure stand, and sorghum and maize (Zea mays L.) in iotercropping and mixed cropping systems, established at Choluteca in southern Honduras. Early instar larvae infested the young sorghum hybrid Catracho (AT × 623 × Tortillero) in pure stand approximately ten days after emergence and persisted throughout the whorl stage (2 June-4 August) during the first growing season (primera) of the crop in 1983. In a small plot study in that year Catracho sorghum and the early maturing native maize variety, Tusa Morada, were planted in alternate hill ('golpe alterno'), alternate row ('surco alterno'), pure stand, and same hill ('casado') systems. Fewer sorghum plants than maize plants were infested with FAW larvae, except in the 'golpe alterno' system. In a third study, using the tropical indigenous sorghum variety Liberal and Tusa Morada maize in 1984, sorghum with a natural weed infestation and the 'casado system' had lower FAW infestations than sorghum with a maize trap crop and pure stand sorghum. A nematode (Mermithidae) was the most common parasite of the FAW in both years. Parasitization (up to 71 %) of larvae by this endoparasitic nematode increased as rainfall increased; precipitation accounted for 93% of the variation in parasitization.