Host-dominated oxidative cascades and transgenerational Cu transfer drive population collapse in Spodoptera frugiperda under chronic CuO nanoparticle exposure: Implications for nano-pesticide environmental risk assessment

The increasing use of CuO nanoparticles (NPs) in agriculture raises urgent concerns about their long-term ecological risks, particularly regarding transgenerational reproduction and gut microbiota in pest species. Here, we chronically exposed Spodoptera frugiperda to a sublethal concentration of CuO NPs (25 mg/kg). Population collapse occurred in the F₄ generation (0 % survival), driven by pronounced oxidative stress (CAT and MDA activities increased up to 2.0-fold), substantial Cu accumulation in eggs (12 → 30 ng/mg) and gut tissue (25 → 750 ng/mg), and impaired reproductive output (33 % reduction in egg production with only 30 % hatching in F₃). Although gut microbial diversity remained structurally stable (Shannon index, P > 0.05), metagenomic analysis revealed functional reprogramming, particularly in energy metabolism. Sterile larva inoculation assays confirmed that microbiota exacerbated toxicity, though direct NPs effects dominated. These findings highlight that current risk assessment frameworks, which are primarily focused on acute toxicity and microbial composition, severely underestimate the hazards of nanopesticides. We advocate for integrating multigenerational toxicity testing and metagenomic profiling into nano-pesticide risk evaluations to better capture population-level outcomes.