Novel β-macrocarpene sesquiterpenoids from maize with inhibition potential against Spodoptera pests via species-specific mechanisms

Phytochemical profiling of maize silk (Yunrui 62) revealed nine novel β-macrocarpene-type sesquiterpenoids (1–9) and the known analog 10, with structures established through integrated NMR, HRESIMS, X-crystallographic, and ECD analyses. Bioassays demonstrated potent anti-insect activity: compounds 2, 3, 6, 7, and 10 significantly suppressed Spodoptera frugiperda larval weight gain, whereas 4 and 10 inhibited S. litura growth at 20 μg/g in artificial diets. Quantitative analysis showed that compound 10 was broadly distributed across various maize tissues. Furthermore, 10 exhibited dose-dependent efficacies against both pests, inducing rapid S. frugiperda mortality by day 3 at 10 μg/g—exceeding azadirachtin’s potency—while maintaining comparable growth inhibition. Mechanistic studies revealed species-specific modes of action: in S. litura, 10 suppressed the expression of detoxification enzymes and digestive trypsin while upregulating the expression of carcinine transporter-like genes; conversely, in S. frugiperda, the genes encoding midgut cellular components were downregulated without impairing detoxification pathways. Our study provides both the molecular blueprints and a direct strategy for enhancing maize resistance through biosynthetic engineering, paving the way for developing next-generation insect-resistant crops.