LAUSR

Simple Summary The fall armyworm, Spodoptera frugiperda (Lepidoptera: Noctuidae), is considered a lepidopteran pest that originated from the Americas. In 2019, the fall armyworm (FAW) was first reported in Taiwan. Alternative host plants also play an important role in the insect population ecology. Hence, the study aimed to investigate how different alternative host plants, two grasses (napier and natal grass) and one legume (sunn hemp) crop, affect the population growth of this insect pest. The findings revealed that alternative host plants significantly affect the developmental period and reproduction of this pest. Based on the age-stage, two-sex life table, sunn hemp resulted to be a more suitable host plant while natal grass a less suitable host plant for FAW. Overall, all alternative host plants could support the growth and development of this pest in the absence of the main host plant. As a result, monitoring the host plants for the pest in the off-season could be used as a technique for prediction. Abstract After being discovered in Taiwan for the first time in June 2019, the polyphagous invasive fall armyworm (FAW), Spodoptera frugiperda (Lepidoptera: Noctuidae), has since spread throughout the entire nation. In Taiwan, this insect has a significant impact on the quality and output of wheat, corn, sorghum, and millet. It may further infest more crops in Taiwan due to its diverse range of hosts and alternate hosts. Maize and other staple crops have already been the subject of several study. The biology of FAW has not yet been studied in relation to the alternative hosts, particularly those commonly found in Taiwanese farmlands. Therefore, this study proposed to investigate the effects of napier grass (Pennisetum purpureum), natal grass (Melinis repens), and sunn hemp (Crotalaria juncea) on the development, reproduction, survivorship, and population growth of FAW under laboratory conditions. According to the results, the developmental duration was considerably the shortest when FAW was reared on sunn hemp while the longest on natal grass. Furthermore, female adults reared on napier grass had a longer adult pre-oviposition period, total pre-oviposition period, oviposition period, longevity, highest fecundity, and highest net reproductive rate (Ro: 465.12). Among the tested three alternative host plants evaluated, sunn hemp had the highest intrinsic rate of increase (r: 0.1993), finite rate of increase (λ: 1.2206), and shortest mean generation time (T: 29.98). Therefore, this study suggests that all hosts plants can contribute to the development and outbreak of this pest in the absence of its primary host; however, sunn hemp was a relatively more suitable host plant for this insect. The possibilities for the FAW’s growth and development vary depending on the host plant. Thereby, all potential host plants in the area should be extensively examined while developing an IPM program against FAW.