Green Nanopesticides from Copper (I) Oxide and Neem Seed Oil: Activity against Cowpea Weevil and Mosquito Larvae.

Abstract

Sustainable alternatives to synthetic pesticides are urgently needed for crop protection and vector control. In this study, a green route to copper(I)-oxide nanoparticles (Cu₂O-NPs) using aqueous Azadirachta indica (neem) leaf extract and their hybridization with neem seed oil (NSO) to yield a bio-nanocomposite (Cu₂O-NPs@NSO) is described. GC-MS revealed that the NSO (29.3% yield) contained biologically active fatty acids, esters, terpenoids, and related constituents. Formation of Cu₂O-NPs was confirmed by UV–Vis (strong UV edge with visible tail), FT-IR (Cu–O bands with phytochemical capping signatures), XRD (cubic Cu₂O; Average crystallite sizes 7.5 nm for Cu₂O-NPs and 6.5 nm for Cu₂O-NPs@NSO), SEM (rough, quasi-spherical particles with moderate agglomeration; increased compactness upon oil loading), EDX (C/O/Cu consistent with capping and oil incorporation), and TGA (12.76% NSO loading). Bioefficacy was evaluated against the storage pest, Callosobruchus maculatus and Anopheles gambiae larvae. Cu₂O-NPs alone showed limited toxicity, whereas NSO was moderately active. The composite displayed pronounced synergy: for C. maculatus, Cu₂O-NPs@NSO achieved 56.7% mortality at 24 h (LC₅₀ 25.63 µg/mL) and 100% at 72 h (LC₅₀ 11.86 µg/mL; LC₉₀ 17.49 µg/mL), outperforming NSO and Cu₂O-NPs. For A. gambiae larvae, Cu₂O-NPs@NSO reached 80.0% mortality at 48 h (LC₅₀ 208.96 µg/mL) and 100%G at 72 h (LC₅₀ 131.85 µg/mL), again surpassing single components. The enhanced activity is attributed to nanoparticle-enabled delivery and controlled release of NSO actives, combined with Cu₂O-mediated membrane disruption and oxidative stress. These results position Cu₂O-NPs@NSO as a promising, biodegradable nanobiopesticide for dual agricultural and public-health applications. Future work should address formulation stability, field validation, and non-target/ecotoxicological profiles to support scalable deployment.