Functional characterization of voltage-gated sodium channels in two mirid pests and identification of kdr mutations in pyrethroid resistant Lygus lineolaris population

Lygus lineolaris and Lygus hesperus are economically important pests that cause substantial damage to wide variety of crops in the United States. In this study, we isolated 17 full-length voltage-gated sodium channels cDNA clones encoding 14 unique splicing variants from a susceptible strain of L. hesperus (sLhNav), two variants from a susceptible L. lineolaris strain (sLlNav), and 8 clones encoding 7 variants from a pyrethroid-resistant L. lineolaris population (rLlNav), based on the usage of 12 alternative exons. Functional expression in Xenopus oocytes revealed that 11 sLh/LlNav variants produced sodium currents suitable for electrophysiological analysis, which displayed distinct gating properties. Notably, Nav variants lacking exon b generated significantly larger currents compared to those including exon b. We also identified A-to-I editing events in both Lygus Navs, and a key finding was the identification of three kdr mutations in rLlNav variants, L1023 F/S in segment IIS6 and L934I in the IIS4-S5 linker (corresponding to L1014F, L1014S and L925I in housefly Nav), all of which have been previously associated with pyrethroid resistance in other insect species. This is the first report of these mutations in resistant L. lineolaris populations. Together with earlier reports of enhanced metabolic detoxification, our findings suggest a dual resistance strategy in L. lineolaris, involving both target-site insensitivity and elevated detoxification enzyme activity. The comprehensive characterization of sodium channel variants in both Lygus, along with the identification of L1023 F/S and L934I mutations, provides valuable insight into Nav diversity in Lygus species and the molecular basis of pyrethroid resistance in L. lineolaris.