Discovery and anti-insect activity of novel terpenoids from Zea mays corn silk against Spodoptera frugiperda

Terpenoids in maize serve as critical defense metabolites, offering protection against pathogens and insect pests. This investigation focused on corn silk (Zea mays), from which 20 terpenoids were isolated—15 diterpenoids (six novel compounds, 1–6) and five sesquiterpenoids (including one new compound, 7). Structural characterization of the novel compounds was achieved through extensive 1D/2D NMR analysis, HRESIMS, and Electronic Circular Dichroism (ECD) spectroscopy. Bioassays against Spodoptera frugiperda larvae demonstrated that compounds 6–8, 10, 13, 18, and 20 significantly reduced larval weight at 20 μg/g (dry weight). Compounds 7 and 20 displayed concentration-dependent inhibitory effects and exhibited comparable efficacy to that of positive control azadirachtin (6 μg/g) at 20 μg/g. The results highlight the potential of maize-derived sesquiterpenoids, particularly 7 and 20, as promising leads for eco-friendly insecticidal agents.