Functional Characterization of Double Mutations T929I/K1774N in the Voltage-Gated Sodium Channel of Megalurothrips usitatus (Bagnall) Related to Pyrethroid Resistance

Megalurothrips usitatus (Bagnall), the main pest on legume vegetables, is controlled by pyrethroids in the field. Field strains of M. usitatus resistant to pyrethroids were collected from three areas in Hainan Province (Haikou, Ledong, and Sanya City), and two mutations, T929I and K1774N, were detected in the voltage-gated sodium channel. In this study, the sodium channel in M. usitatus was first subcloned and successfully expressed in Xenopus oocytes. The single mutation (T929I or K1774N) and double mutation (T929I/K1774N) shifted the voltage dependence of activation in the hyperpolarization direction. The three mutants all reduced the amplitude of tail currents induced by type I (permethrin and bifenthrin) and type II (deltamethrin and λ-cyhalothrin) pyrethroids. Homology modeling analysis of these two mutations shows that they may change the local hydrophobicity and positive charge of the sodium channel. Our data can be used to reveal the causes of the resistance of M. usitatus to pyrethroids and provide guidance for the comprehensive control of M. usitatus in the future.