Biosynthesis of silver nanoparticles using <i>Vitex negundo</i>: Pesticidal efficacy against <i>Spodoptera litura</i> and <i>Helicoverpa armigera</i> with a safety assessment

Plant-based metallic nanoparticles hold promise for agricultural applications. This study investigated the biosynthesis of silver nanoparticles (AgNPs) using Vitex negundo leaf extract. It assessed their pesticidal properties and safety. AgNPs were synthesized via aqueous extract and characterized by UV–Vis spectroscopy, dynamic light scattering (DLS), Scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier-transform infrared spectroscopy (FTIR) Characterization revealed a surface plasmon resonance (SPR) peak at 435 nm, an average particle size of 236.4 nm, and a stable zeta potential. SEM confirmed spherical morphology, XRD indicated a face-centred cubic (fcc) structure, and FTIR confirmed biomolecule-mediated capping and stabilization. Larvicidal bioassays showed that 5 mg/L AgNPs caused 78-89% mortality in Spodoptera litura and 83-100% in Helicoverpa armigera. In both pests, oxidative stress was triggered. Catalase (CAT) activity increased by over 80% in S.litura and moderately in H. armigera. Glutathione-S-transferase (GST) activity declined post-treatment, from 9.4 to 5.0 mM/min/mg protein in H. armigera and from 1.0 to 0.7 mM/min/mg protein in S. litura, indicating impaired detoxification. In Oreochromis urolepis, AgNPs (5, 10, and 25 mg/L) induced oxidative stress without mortality. CAT activity decreased within 24 hours (72.4% at 5 mg/L) and remained suppressed by day 5 (36.7% at 25 mg/L). Superoxide dismutase (SOD) activity increased at 5 mg/L (19.8%) and 25 mg/L (54.8%), while GST initially declined but rebounded at higher concentrations. Reduced glutathione (GSH) levels increased by 24.3% at 25 mg/L, indicating adaptation. This study highlights that V. negundo-derived AgNPs are effective, eco-friendly biopesticides with minimal non-target toxicity.