Abstract: 【Aim】To explore the safety of commonly used insecticides to the natural enemy Picromerus lewisi and their impact on predation function.【Methods】The spraying method was applied to detect the median lethal concentration (LC₅₀) values of 14 insecticides of 6 categories ［broflanilide, cyantraniliprole, chlorantraniliprole and flubendiamide (diamides), lambda-cyhalothrin (pyrethroids), imidacloprid, flupyradifurone and sulfoxaflor (neonicotinoids and analogues), triflumezopyrim (mesoionics), emamectin benzoate, spinosad and abamectin (macrolides), and bioinsecticides (Bacillus thuringiensis and Metarhizium anisopliae CQMa421)］ against the 3rd instar nymphs of P. lewisi, and the safety factor was used to evaluate their safety to P. lewisi. In addition, the predatory efficiency of the 3rd instar nymphs of P. lewisi treated with four insecticides mentioned above (lambda-cyhalothrin, cyantraniliprole, imidacloprid and abamectin) on the 2nd and 3rd instar larvae of Mythimna seperata was analyzed using the disc equation. 【Results】Chlorantraniliprole, cyantraniliprole and abamectin exhibited relatively high safety levels to the 3rd instar nymphs of P. lewisi, and flubendiamide demonstrated the highest safety to the 3rd instar nymphs of P. lewisi, with the LC₅₀ value of 369.71 mg/L in 24 h and the safety factor of 7.39. In contrast, lambda-cyhalothrin, imidacloprid and broflanilide exhibited lower safety to the 3rd instar nymphs of P. lewisi, and broflanilide showed the lowest safety to the 3rd instar nymphs of P. lewisi, with the LC₅₀ value of 0.01 mg/L in 24 h and the safety factor of below 0.01. After 48-h treatment, sulfoxaflor, chlorantraniliprole, flubendiamide and cyantraniliprole maintained relatively high safety to the 3rd instar nymphs of P. lewisi, and flubendiamide was recorded to have the highest safety to the 3rd instar nymphs of P. lewisi, with the LC₅₀ value of 299.28 mg/L and the safety factor of 5.99. Conversely, broflanilide, imidacloprid and lambda-cyhalothrin exhibited lower safety to the 3rd instar nymphs of P. lewisi, and broflanilide had the lowest safety to the 3rd instar nymphs of P. lewisi, with the LC₅₀ value of 0.04 mg/L in 48 h and the safety factor of below 0.01. The bioinsecticides M. anisopliae CQMa421 and B. thuringiensis were found to be relatively safe to the 3rd instar nymphs of P. lewisi. Compared to the control treated with 0.1% Triton X-100, the stress from the four insecticides (lambda-cyhalothrin, cyantraniliprole, imidacloprid and abamectin) reduced the predation efficiency of the 3rd instar nymphs of P. lewisi, although had no significant effect on the instantaneous attack rate. Notably, under the stress of 20 mg/L cyantraniliprole, the 3rd instar nymphs of P. lewisi had the highest instantaneous attack rates (0.623 and 0.586, respectively) on the 2nd and 3rd instar larvae of M. seperata.  Under the stress of 2 mg/L abamectin, the 3rd instar nymphs of P. lewisi nymphs had the shortest handling time for prey (0.091 and 0.076 d, respectively), the highest maximum daily predation amount (11.00 and 13.12 individuals, respectively) and the highest predatory efficiency (4.72 and 5.34, respectively) on the 2nd and 3rd instar larvae of M. seperata, while under the stress of 2 mg/L imidacloprid, the 3rd instar nymphs of P. lewisi had the lowest predation efficiency (2.46 and 2.08, respectively) on the 2nd and 3rd instar larvae of M. seperata. 【Conclusion】Chlorantraniliprole, flubendiamide and M. anisopliae CQMa421 demonstrated higher safety to P. lewisi nymphs, whereas broflanilide and imidacloprid exhibited lower safety to P. lewisi nymphs. Additionally, treatments with abamectin and cyantraniliprole had minimal impact on the predation capability of P. lewisi nymphs, while imidacloprid treatment significantly affected their predation capability. These findings play a crucial role in providing information for pest management strategies in agricultural environments by minimizing the toxicity of insecticides.

Key words:  Picromerus lewisi, Mythimna seperata, pesticide, safety, predation efficiency