Enhancing the biological efficacy of clove extract via silver nano-loading to combat the stored drug beetle (Coleoptera: Anobiidae )

Abstract

Growing environmental and resistance concerns have spurred the search for sustainable botanical insecticides to replace synthetic fumigants in stored-product protection. To address this need, this study evaluated the contact toxicity of clove (Syzygium aromaticum) extracts using both aqueous and ethanolic extracts as well as a novel formulation of silver nanoparticle-enhanced aqueous extract (AgNPs) against adults of the drugstore beetle, Stegobium paniceum. Filter paper bioassays were conducted at concentrations of 5%, 10%, 15%, and 20% (v/v), with mortality recorded after 6, 12, and 24 hours. Results demonstrated that the structural characterization (SEM, EDX, FT-IR) confirmed the successful synthesis of spherical, crystalline AgNPs with an average diameter of 28.34 ± 1.203 nm, stabilized by polyphenolic phytoconstituents. The AgNP-enhanced extract was the most potent formulation, exhibiting a 24-hour LC₅₀ of 1.52 % . This represents a 4.34-fold increase in potency over the aqueous extract alone (LC₅₀ = 6.60%), while the ethanolic extract had an LC₅₀ of 2.50%. Statistical analysis (ANCOVA) confirmed that the nanoparticle enhancement caused a significant increase in mortality of approximately 21%. These results demonstrate that clove-based extracts, particularly the nano-formulation, present a promising and biodegradable alternative to synthetic insecticides for protecting stored products.