Revealing the hidden resource of fall armyworm Spodoptera frugiperda (Lepidoptera: Noctuidae): Asteraceae weeds as alternative hosts

While the fall armyworm, Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae), has invaded Asia, whether it uses local weeds as alternative hosts remains understudied. This knowledge gap is significant as alternative hosts may facilitate fall armyworm expansion. Here we conducted three experiments to investigate the potential use of Asteraceae weeds (Emilia sonchifolia var. javanica [E. sonchifolia hereafter] and E. praetermissa) by fall armyworm in Taiwan: (1) The feeding experiment examined fall armyworm performance on the two Emilia species against the control (artificial diet). (2) The host-plant shift experiment tested if fall armyworm can survive on the Emilia species after depleting its primary host (maize). (3) Spatial analysis mapped current fall armyworm invasions, maize production areas, and the distribution of Emilia host plants (if confirmed) to demonstrate the potential of Asteraceae weeds as fall armyworm’s untapped resource. The results indicated that fall armyworm could complete its life cycle on E. sonchifolia but not E. praetermissa. Compared to the control, both sexes of fall armyworms on E. sonchifolia performed similarly in survivorship, larval weight, larval and pupal duration, but worse in pupal length and weight. In addition, larvae can switch to E. sonchifolia after depleting maize, reaching adult emergence and producing fertile eggs. The spatial analysis demonstrated hotspots of fall armyworm invasions and a large area of E. sonchifolia as potential food resource for future fall armyworm expansion. Overall, our results raise concerns that overlooking the use of weeds from the Asteraceae family may lead to an underestimation of future fall armyworm expansion.