Toxic and Sublethal Effects of Commonly Used Pesticides on Neoseiulus barkeri (Acari: Phytoseiidae)

Neoseiulus barkeri is an important predatory mite used for biological control in citrus orchards in China. Systematic studies on the toxicity of commonly used pesticides to predatory mites are rarely reported. In this study, we developed a "four-well volcanic dish" bioassay system to determine the acute contact toxicity of 33 pesticides registered in citrus, and further evaluated the sublethal effects of chlorpyrifos, lambda-cyhalothrin, and chlorfenapyr at LC₁₀ and LC₂₀ on the development and reproduction of N. barkeri. Amitraz was the most toxic compound, with an LC₅₀ of 55.92 mg/L. Chlorpyrifos, chlorfenapyr, lambda-cyhalothrin, glufosinate-ammonium, and beta-cyfluthrin also showed relatively high toxicity, with LC₅₀ values of 100-400 mg/L, whereas many other pesticides were much less toxic, with LC₅₀ values above 1000 mg/L. LC₂₀ exposure to chlorpyrifos, lambda-cyhalothrin, or chlorfenapyr significantly prolonged development, reduced fecundity, and shortened female longevity. LC₂₀ treatments also decreased the net reproductive rate (R₀) and intrinsic rate of increase (r_m), indicating reduced population growth potential. This study clarified the toxic effects of various pesticides on predatory mites and further elucidated the sublethal effects of three broad-spectrum pesticides on these mites. These findings provide a theoretical basis for coordinating chemical and biological control in citrus IPM programs.