<p>The fall armyworm (<i>Spodoptera frugiperda</i>) is a polyphagous migratory pest that can disperse among various host plants within a certain area. It is known to reduce crop yields, particularly in corn, by approximately 15–20%. Additionally, the fall armyworm follows seasonal changes and feeds successively, complicating monitoring and integrated management efforts. Therefore, understanding how host-plant switching affects the growth and development of the fall armyworm and examining its adaptive responses can provide valuable theoretical insights for its monitoring and control. This article selected eight plant species from the field, including Corn (<i>Zea mays</i> L.), wheat (<i>Triticum aestivum</i> L.), Veronica (<i>Veronica didyma Tenore</i>), spurge (<i>Euphorbia bupleurifolia</i>), chickweed (<i>Stellaria media</i>), hairy flower millet grass (<i>Setaria italica</i>), wild germander (<i>Teucrium chamaedrys</i>), and stitchwort (<i>Stellaria holostea</i>), and ultimately established five strains of fall armyworms that have undergone host-plant switching. Subsequently, we investigated the physiological and transcriptomic responses of <i>S. frugiperda</i> to host-plant switching, utilizing controlled experiments to assess its growth, feeding behavior, and gene expression after host-plant switching. The research results provide a theoretical basis for the development of new targets for plant resistance to insects and pest control, offer new ideas for the early warning and control of this pest, and provide a scientific basis for deepening the understanding of the ecological adaptation mechanisms of the fall armyworm.</p>