Detection of Putative Mutation I873S in the Sodium Channel of Megalurothrips usitatus (Bagnall) Which May Be Associated with Pyrethroid Resistance

Simple Summary Megalurothrips usitatus is the main pest of cowpea in China, mainly by feeding on plant leaves and spreading plant viruses. In this study, a new mutation putative site, I873S, was correlated with pyrethroid resistance. According to the results of the bioassay, an I873S mutation may be associated with the resistance of M. usitatus to pyrethroids. The results of this study will promote the development of research on the resistance of M. usitatus to pyrethroids and provide guidance for improving the management system of M. usitatus in the future. Pyrethroid resistance of thrips has been reported in many countries, and knockdown resistance (kdr) has been identified as a main mechanism against pyrethroids in many insects. To characterize pyrethroid resistance in Megalurothrips usitatus from the Hainan Province of China, we conducted a biological assay and sequenced the voltage-gated sodium channel gene domain II from M. usitatus field populations. It showed high resistance to the pyrethroids for 2019 and 2020, in which LC50 to lambda-cyhalothrin of M. usitatus was 1683.521 mg/L from Sanya in 2020. The LC50 value of deltamethrin was lower in Haikou than in other locations, which mean the south of Hainan has higher resistance than the north of Hainan. Two mutations of I873S and V1015M were detected in the domain II region of the sodium channel in M. usitatus; however, the mutation frequency of V1015M was only 3.33% and that of I873S was 100%. One is homozygous and the other is a heterozygous mutant type. The three thrips-sensitive strains of sodium channel 873 are highly conserved in amino acids (isoleucine), while the M. usitatus pyrethroid-resistant strains are all serine, so I873S may be related to the resistance of M. usitatus to pyrethroids. The present study will contribute to the understanding of the evolution of pyrethroids resistance and contribute to the development of resistance management of M. usitatus in Hainan.