Efficacy of Biogenically Synthesized ZnO Nanoparticles by Hyptis suaveolens Leaf Extract against Cowpea Weevil (Callosobruchus maculatus) for Pesticidal Activity

This study reports the green synthesis and multifunctional evaluation of zinc oxide nanoparticles (ZnO NPs) using Hyptis suaveolens leaf extract. Fresh leaves were shade-dried, pulverized, and extracted to prepare the bio-reducing precursor, with zinc sulfate used as the metallic source. A color shift from deep green to pale yellow confirmed nanoparticle formation. The synthesized ZnO NPs were characterized by XRD, SEM, EDX, and FTIR, revealing crystalline, spherical particles stabilized by phytochemicals. Antibacterial assays demonstrated strong inhibitory activity against Bacillus subtilis, Pseudomonas aeruginosa, and Enterococcus faecalis, with Gram-positive strains showing higher sensitivity. Pesticidal bioassays against Callosobruchus maculatus showed dose-dependent mortality, reduced adult emergence, seed damage, and weight loss, along with enhanced seed protection. At higher concentrations (750–1050 ppm), ZnO NPs achieved complete adult suppression; however, 1050 ppm slightly reduced seed germination. These findings highlight H. suaveolens-mediated ZnO NPs as eco-friendly, dual-functional agents for sustainable pest and microbial management in agriculture.