Abstract: 【Aim】Diaphorina citri and Xanthomonas citri subsp. citri (Xcc) are two major pests and diseases that seriously hinder the sustainable development of citrus industry in our country, and their current control methods are limited. Silver nanoparticles (AgNPs) and nano-silicon dioxide (SiO₂ NPs) exhibit insecticidal and antibacterial activities, holding potential application prospects for the control of agricultural pests and diseases. This study aims to test the toxicity of Ag-SiO₂ nanocomposite to D. citri and the antibacterial activity against Xcc, offering a novel measure for effective control of citrus pests and diseases.【Methods】In a controlled laboratory setting, we tested the toxicity of Ag-SiO₂ nanocomposite at the concentrations of 1, 2, 4, 8 and 16 mg/mL to the early (1st-2nd instar) nymphs, late (3rd-5th instar) nymphs, and adults of D. citri by immersion method, and calculated the corrected mortality rates of D. citri and the median lethal concentration (LC₅₀) values of Ag-SiO₂ nanocomposite against different developmental stages of D. citri at 24, 48 and 72 h after treatment. Meanwhile we investigated the alterations in morphology and behavior of D. citri at 24 and 48 h after treatment with Ag-SiO₂ nanocomposite using optical microscopy and scanning electron microscopy, and tested the antibacterial activities of Ag-SiO₂ nanocomposite at the concentrations of 100, 200, 400, 800 and 1 600 μg/mL targeting Xcc by inhibition zone method, measured the diameter of the inhibition zone using the cross method, and calculated the relative antibacterial rate and the medium effective concentration (EC₅₀) value at 48 h after treatment. 【Results】At 72 h after treatment, the corrected mortality rates of the early and late nymphs, and adults of D. citri caused by Ag-SiO₂ nanocomposite at the concentration of 8 mg/mL reached 97.50%, 85.00% and 57.14%, respectively, and the LC₅₀ values of Ag-SiO₂ nanocomposite against the early and late nymphs, and adults of D. citri were 1.3949, 1.9650 and 5.4648 mg/mL, respectively. At 48 h after treatment, the relative antibacterial rate of Ag-SiO₂ nanocomposite at the concentration of 1 600 μg/mL against Xcc reached 53%, and the EC₅₀ value of Ag-SiO₂ nanocomposite against Xcc in 48 h was 1.1853 mg/mL.【Conclusion】Ag-SiO₂ nanocomposite exhibited obvious toxicity to D. citri and also inhibited the activity of Xcc. Ag-SiO₂ nanocomposite exhibited promising potential as both efficient insecticide against D. citri and efficient fungicide for Xcc in the control of citrus pests and diseases, providing a theoretical basis for the pesticide development and field application in the integrated management of citrus pests and diseases.

Key words: Diaphorina citi, Xanthomonas citri subsp. citri, Ag-SiO₂, nanocomposite, insecticidal activity, antibacterial activity