pH-responsive λ-cyhalothrin nanopesticides for effective pest control and reduced toxicity to Harmonia axyridis

In this study, pH-responsive LC@O-CMCS/PU nanoparticles were prepared by encapsulating λ-cyhalothrin (LC) with O-carboxymethyl chitosan (O-CMCS) to form LC/O-CMCS and then covering it with polyurethane (PU). Characterization and performance test results demonstrate that LC@O-CMCS/PU had good alkaline release properties and pesticide loading performance. Compared to commercial formulations containing large amounts of emulsifiers (e.g., emulsifiable concentrate, EC), LC@O-CMCS/PU showed better leaf-surface adhesion. On the dried pesticide-applied surfaces, the acute contact toxicity of LC@O-CMCS/PU to Harmonia axyridis (H. axyridis) was nearly 20 times lower than that of LC EC. Due to the slow-releasing property of LC@O-CMCS/PU, only 16.38 % of LC was released at 48 h in dew and effectively reduced the toxicity of dew. On the pesticide-applied leaves with dew, exposure to the LC (EC) caused 86.66 % mortality of H. axyridis larvae significantly higher than the LC@O-CMCS/PU, which was only 16.66 % lethality. Additionally, quantitative analysis demonstrated 11.33 mg/kg of λ-cyhalothrin in the dew on LC@O-CMCS/PU lower than LC (EC) with 4.54 mg/kg. In summary, LC@O-CMCS/PU effectively improves the safety of λ-cyhalothrin to H. axyridis and has great potential to be used in pest control combining natural enemies and chemical pesticides.