Chitosan-grafted polylactic acid as a novel pesticide carrier: optimizing etoxazole release, boosting mite control,...

Conventional acaricides face challenges of environmental persistence and non-target toxicity. To address this, a chitosan-grafted polylactic acid (CS-co-PLA) controlled-release system was rationally designed as a biodegradable carrier for etoxazole (Eto), aiming to enhance acaricidal efficacy while minimizing ecological risks. This study focuses on synthesizing Eto@CS-co-PLA through ring-opening polymerization and evaluating its controlled-release behavior, bioactivity against Tetranychus urticae and environmental biosafety.

The hexahedron-shaped Eto@CS-co-PLA exhibited a uniform particle size (3.45 ± 0.77 μm, scanning electron microscopy) with 9.05% drug loading. The release followed first-order kinetics (R² = 0.986), with the CS-co-PLA carrier showing slowed release in later stages. At 72 h, cumulative release reached 83.65% for R-etoxazole and 82.44% for S-etoxazole. Bioassays revealed superior ovicidal activity (median lethal concentration = 0.170 mg L^-1), 1.5-fold lower than free Eto (0.259 mg L^-1; P < 0.001), but no acute toxicity to adult mites or earthworms. Enhanced leaf adhesion (contact angle: 45 ± 2.2° versus 63.4 ± 2.5° for Eto) and adhesion work ensured reduced environmental loss. Biosafety assessments demonstrated crop growth promotion and non-target safety.

The Eto@CS-co-PLA controlled-release system demonstrated excellent slow-release capabilities, achieving high efficacy against T. urticae without acute toxicity to adult mites and earthworms. Its biodegradability and plant growth-promoting properties ensured minimal environmental impact. This study provides a sustainable paradigm for precision application of agricultural chemicals, achieving a balance between insecticidal efficiency and ecological safety. © 2025 Society of Chemical Industry.