Broad-spectrum defence in maize induced by Spodoptera frugiperda feeding against Lepidoptera pests based on secondary metabolome analysis

The invasion of the fall armyworm (FAW), Spodoptera frugiperda, has markedly altered the community structure of Lepidoptera pests in maize fields. This study systematically evaluated the inhibitory effects of FAW feeding-induced defence in maize against other Lepidoptera pests through field artificial infestation assays and laboratory bioassays, and elucidated the underlying chemical basis using secondary metabolomics and bioactive screening. Field experiments demonstrated that pre-infestation by FAW significantly reduced the population densities of Ostrinia furnacalis and Mythimna loreyi, but had no significant impact on Helicoverpa armigera. Laboratory experiments further confirmed that feeding on FAW-pretreated leaves significantly suppressed the weight gain and feeding preference of O. furnacalis and M. loreyi larvae, whereas H. armigera remained unaffected, revealing the species-specific nature of this induced resistance. Metabolomic analysis and toxicity screening revealed that methyl nicotinate (MN), chlorogenic acid (CA), umbelliferone (Um), and 6-Methoxy-2-benzoxazolinone (MBOA), which accumulated significantly after FAW herbivory, exhibited significant antifeedant, lethal or growth inhibitory activity against FAW and/or M. loreyi. This study clarifies that FAW feeding induces the production of specific defensive metabolites in maize, which asymmetrically affect the population establishment of subsequent pests. It provides insights into the interspecific competition mediated by induced defence of maize and offers novel chemical targets for developing multi-target, eco-friendly pest management strategies based on plant-induced defence.