Abstract: 【Aim】 The objective of this research is to clarify the resistance level and resistance stability of chlorantraniliprole in the rice leaffolder, Cnaphalocrocis medinalis, and to determine whether there are cross-resistance to other diamide insecticides in chlorantraniliprole-resistant populations. 【Methods】 The rice seedling dipping method was adopted to determine the resistance of 32 field populations of C. medinalis collected from nine provinces (autonomous regions) to chlorantraniliprole and tetraniliprole, the cross-resistance to other diamide insecticides in two chlorantranilipeole-resistant populations, and the resistance stability when the populations from Youxian, Hunan, Qianshan, Anhui, Lujiang, Anhui and Xing′an,Guangxi were not exposed to chlorantraniliprole in laboratory. 【Results】 The resistance of chlorantraniliprole in C. medinalis field populations kept increasing during 2019-2022. Lujiang, Xing′an, Wuxue, Danyang and Qianshan populations were monitored for the first time to have developed high level of resistance to chlorantraniliprole (102.3-135.1-fold), and other populations also reached moderate level of resistance (10.3-97.1-fold) in 2022. To tetraniliprole, all the monitored field populations kept susceptible during 2019-2021, while the populations monitored in 2022 have developed moderate level of resistance (41.9-98.0-fold). Moreover, the cross-resistance experiment results revealed that Jiaxing and Qianshan populations which appeared about 100-fold resistance to chlorantraniliprole also showed 31.6-100.5-fold cross-resistance to cyhalodiamide, tetraniliprole, cyantraniliprole, cyclaniliprole and tetrachlorantraniliprole. In addition, the chlorantraniliprole resistance of field populations decreased rapidly after 2-4 generations of successive rearing without exposure to insecticides in laboratory. 【Conclusion】 The field populations of C. medinalis have developed moderate to high level of resistance to chlorantraniliprole and tetraniliprole. Moderate to high level of cross-resistance to five other diamide insecticides was found in chlorantraniliprole-resistant populations. Besides, the resistance to chlorantraniliprole was unstable in C. medinalis field populations. So, we strongly suggested limiting or suspending the application of diamide insecticides in order to delay the resistance development and postpone the application of diamide insecticides in C. medinalis control in the future.

Key words: Cnaphalocrocis medinalis, resistance monitoring, chlorantraniliprole, cross-resistance, resistance stability