Evaluation of bioactivity and field efficacy of seven insecticides to lepidopterous pests

To clarify the insecticidal activity and field efficacy of seven insecticides （IRAC 28 group: chlorantraniliprole, cyantraniliprole, tetrachlorantraniliprole, tetraniliprole and thiotraniliprole, IRAC 30 group: broflanilide and isocycloseram）on lepidopterous pests, the bioactivity assays against Plutella xylostella, Spodoptera exigua, Helicoverpa armigera and Chilo suppressalis were performed by immersion method, and the field trials were conducted to evaluate the control efficacy on P. xylostella and S. exigua. The bioassay showed that the toxicities of isocycloseram against P. xylostella, S. exigua and C. suppressalis were the highest, with LC₅₀ values of 0.0040, 0.0521 and 0.0078 mg/L, respectively. Followed by broflanilide, the LC₅₀ values were 0.0198, 0.0584 and 0.0339 mg/L, respectively. The LC₅₀ values of the other five insecticides against P. xylostella, S. exigua and C. suppressalis were 0.0212-0.1378 mg/L, 0.2577-0.8080 mg/L and 0.2886-1.2277 mg/L, respectively. The toxicity of thiotraniliprole against H. armigera was an highest with the LC₅₀ value of 0.0218 mg/L, which was significantly higher than that of the other 6 insecticides (LC₅₀ values were 0.0694-0.2747 mg/L). The field trials for controlling P. xylostella showed that the control efficacy of IRAC 30 group insecticides at a dose of 30 a.i. g/hm² was 95.60%-96.68% at 7 d after treatment, significantly higher than that of IRAC 28 group insecticides at the dose of 30 a.i. g/hm² and 60 a.i. g/hm² (49.07%-81.77% and 57.47%-85.90%). The control efficacy of thiotraniliprole, cyantraniliprole and tetrachlorantraniliprole was over 80% at the dose of 60 a.i. g/hm², which was higher than that of chlorantraniliprole (57.47%). The control efficacy of broflanilide against S. exigua was 96.45% after 7 d treatment at a dose of 22.5 a.i. g/hm², which was higher than that of the other six insecticides at a dose of 22.5 and 45 a.i. g/hm² (62.34%-86.75% and 68.06%-85.56%). Chlorantraniliprole showed the weakest effect on S. exigua (62.34%). The research showed that the seven insecticides tested had high activity against four lepidopterous pests, but variations of control effect existed under field trials. Field populations of P. xylostella and S. exigua were likely to have developed different levels of resistance to insecticides in IRAC 28 group. Corresponding resistance management strategies need to be launched timely and the development and application of insecticides in IRAC 30 group need to be accelerated.