Abstract: 【Aim】 This study aims to make green synthesis of silver nanoparticles (AgNPs) using aqueous extracts of multiple medicinal plants, and to detect and analyze their toxicity and action mechanism against the Formosan subterranean termite, Coptotermes formosanus, so as to explore the potential of AgNPs in termite control and expand its future application in agriculture. 【Methods】 The aqueous extracts of four medicinal plants including root of rhubarb (Rheum palmatum), plants of decumbent bugle herb (Ajuga nipponensis), root of lightyellow sophorn (Sophora flavescens) and plants of houttuynia (Houttuynia cordata) were used as the raw materials to synthesize AgNPs. The formation of AgNPs was characterized by UV-visiblespectroscopy (UV-vis), scanning electron microscopy (SEM), transmission electronmicroscopy (TEM), X-ray energy dispersive spectrum(EDS) and nanoparticle size analyzer to assess the size, shape and aggregation degree of AgNPs. Then, the toxicity of AgNPs to C. formosanus workers was measured in the laboratory condition and the action mechanism of AgNPs on termites was explored by determining the soluble protein content, acetylcholinesterase (AchE) activity and filter paper activity (FPA) in C. formosanus workers at 7 d after treatment with 800 mg/L AgNPs.【Results】 The green synthesized AgNPs with the aqueous extracts of four medicinal plants were spherical particles, with an average particle diameter of 69-180 nm. The LC₅₀ values of AgNPs against C. formosanus workers in 7 d were 150, 340, 342 and 309 mg/L, respectively. The soluble protein contents, AchE activities and FPA in C. formosanus workers at 7 d after treatment with 800 mg/L AgNPs were significantly decreased compared with those in the control. 【Conclusion】 AgNPs synthesized by four plant extracts show high toxicity to C. formosanus workers, and the survival of termites can be affected by AgNPs by reducing the soluble protein content, AchE activity and FPA, suggesting that AgNPs have great potential in control of C. formosanus.

Key words: Coptotermes formosanus, silver nanoparticles, plant extracts, green synthesis, insecticidal activity, action mechanism