Development of Metal–Organic Framework-Based Emamectin Benzoate Nanopesticides for Effective Control of Bursaphelenchus xylophilus

Pine wilt disease is caused by Bursaphelenchus xylophilus invasion and has a great impact on global pine resources. Injection of emamectin benzoate (EB) into pine trunks is an effective way to control B. xylophilus. However, EB has limited aqueous solubility, easily photodissociates, and its long-term use causes resistance problems. In this study, the metal-organic framework material ZIF-8 was prepared, and EB was loaded onto ZIF-8 through physical adsorption, resulting in a pH-responsive EB@ZIF-8 nanopesticide with a high drug loading rate (36.04%). Simulated release experiments of EB@ZIF-8 under different pH conditions showed a cumulative release of 64.43% within 10 h at pH 5.0, which increased as the pH decreased, compared to conditions at pH 7.0 and 9.0. EB@ZIF-8 showed positive insecticidal activity in a laboratory biological test (LC₅₀ = 52.503 mg/L). In addition, 7 days after trunk injection in Pinus massoniana, EB residuals were detected in all parts of the branches, with the lowest residue level being 73.39 mg/kg. The proportion of the EB residue in the lower, middle, and upper branches of P. massoniana gradually increased, reaching 43.92% at 28 days after trunk injection, indicating that EB was distributed evenly in the tree. Therefore, EB@ZIF-8 had good morphology, structure, and pH-responsive release performance. EB@ZIF-8 also exhibited a high nematocidal ability due to its smaller particle size and rapid transport in P. massoniana. This study provides a new approach for the development of highly effective EB preparations, improvement of pesticide utilization, and B. xylophilus control.