Identification Of Point Mutations Related To Pyrethroid Resistance In Voltage-Gated Sodium Channel Genes In Aphis Glycines

Knockdown resistance (kdr) and super-kdr (skdr) point mutations have been identified in the voltage-gated sodium channel (vgsc) para genes in several aphid species with resistance to pyrethroids, but have not been confirmed in Aphis glycines Matsumura (Hemiptera: Aphididae), a serious soybean crop pest with resistance to pyrethroids. We used the A. glycines genome assembly GenBank accession number VYZN00000000 to mine potential vgsc para-ortholog genes, and amplicon-seq to screen for kdr and skdr mutations in nine populations from North Central USA with different pyrethroid susceptibility, sampled in 2018-2019. As was found in other aphids, two putative vgsc genes (vgsc1 and vgsc2) were identified in the same scaffold, oriented in opposite directions similar to 4 kb distant from each other. The vgsc1 gene coded heterodimer 1 (AglNav1) containing the VGSC domains I and II, while vgsc2 coded heterodimer 2 (AglNav2) with domains III and IV. Three splice variants were identified for each vgsc gene. The mutations M918L (skdr), M918I and L925M were identified in domain II in the IIS4-IIS5 linker region, and mutation L1014F (kdr) in the IIS6 segment. Although all mutations were found as heterozygotes, the population with the single M918L mutation and most populations with multiple mutations (M918I+L1014F or L925M+L1014F) exhibited a pyrethroid resistance phenotype, confirmed by lambda-cyhalothrin exposure bioassays. The kdr and skdr point mutations in soybean aphid are the same point mutations associated with the target site insensitivity to pyrethroids in other arthropods and very likely contribute to resistance in soybean aphid.