Abstract: 【Aim】 To ascertain the resistance levels of the field populations of Rhopalosiphum padi from the Guanzhong Region of Shaanxi Province, nothwestern China to five pyrethroid insecticides and analyze the correlations between the mutation frequencies of the voltage-gated sodium channel (VGSC) gene (the target gene of pyrethroid) of various field populations and resistance levels. 【Methods】Nine field populations of R. padi were collected from the Guanzhong Region of Shaanxi Province during April-June in 2023 and 2024 and the susceptibility of the apterous adults to five pyrethroid insecticides (bifenthrin, permethrin, lambda-cyhalothrin, deltamethyrin and fenvalerate) was tested by leaf-dipping method. PCR was used to detect the types and frequencies of VGSC gene mutation of various field populations of R. padi. The correlation between the mutation frequency and the resistance level (resistance ratio, RR) was analyzed. 【Results】Bioassay results revealed that the apterous adults of various field populations of R. padi exhibited varying degrees of resistance to five pyrethroid insecticides. The apterous adults of the population collected from Xingping County, Xianyang City in 2023 (XP-2023) showed the highest resistance levels to type Ⅰ pyrethroid insecticides (bifenthrin and permethrin), with the RRs of 76.1 and 52.3, respectively. The apterous adults of the populations collected from Fufeng County, Baoji City in 2024 and 2023 (FF-2024 and FF-2023) and the population collected from Liquan County, Baoji City in 2023 (LQ-2023) showed the highest resistance levels to type Ⅱ pyrethroid insecticides (lambda-cyhalothrin, deltamethrin and fenvalerate), with the RRs of 60.7, 97.5 and 42.6, respectively. Detection of VGSC gene mutations revealed that, except for the populations collected from Wugong County, Xianyang City and Qishan County, Baoji City, respectively, in 2023 (WG-2023 and QS-2023), all the field populations carried heterozygous mutation (M918L) in the VGSC gene, with the mutation frequencies ranging from 5.0% to 47.5%. The mutation frequency of M918L was significantly correlated with the level of resistance to pyrethroid insecticides. 【Conclusion】The M918L heterozygous mutation in the VGSC gene is significantly correlated with the resistance levels of the field populations of R. padi to pyrethroid insecticides, indicating that this target mutation plays an important role in the resistance of the field populations of R. padi to these insecticides. It is recommended to minimize or avoid the use of pyrethroid insecticides in field control of R. padi and to continuously monitor the resistance levels of field populations.

Key words: Rhopalosiphum padi, pyrethroid, resistance monitoring, target mutation, voltage-gated sodium channel, gene mutation