Insecticide resistance of field populations of Mythimna separata in Shaanxi and Shanxi province

Resistance of five field populations of Mythimna separata (Walker), which collected respectively from Chang'an district, Huayin county, Sanyuan county, Xingping city in Shaanxi province and Taigu county in Shanxi province of China, to six insecticides was evaluated by leaf dip method in laboratory. The results showed that the populations of M. separata in those five areas were relatively sensitive to emamectin benzoate (resistance ratio 0.6-1.6 fold). In terms of chlorantraniliprole and beta-cypermethrin, those five field populations of M. separata showed susceptible to low level resistance (RR 0-6.2). Compared with the relative susceptible strain of M. separata, those five field populations showed susceptible to moderate resistance level to chlorpyrifos and lambda-cyhalothrin (RR 0.1-32.8). Resistance to phoxim was moderate to high level in all the tested populations (RR 19.4-70.1) except for the Sanyuan population. Pair-wise correlation analysis among different insecticides indicated that chlorpyrifos has a positive and significant correlation with emamectin benzoate. However, chlorantraniliprole has no significant correlation with emamectin benzoate, chlorpyrifos or phoxim. Therefore, emamectin benzoate, chlorantraniliprole and beta-cypermethrin were recommended for the control of oriental armyworm. Meanwhile, to delay the generation and development of insecticide resistance in Shaanxi and Shanxi province, rotational application of insecticides between chlorantraniliprole and emamectin benzoate or chlorpyrifos is necessary.