Molecular analysis of the para-sodium channel gene in the pyrethroid-resistant diamondback moth, Plutella xylostella (Lepidoptera

Resistance to pyrethroids in the diamondback moth (DBM), Plutella xylostella, has been shown to be conferred by nerve insensitivity. In the present study, amino acid sequences corresponding to the domain IIS4-IIS6 region of the para-sodium channel, which is known to be significant for nerve insensitive pyrethroid resistance in a variety of insects, were compared between pyrethroid-resistant (R) and non-selected (NS) strains. Thr to Ile and Leu to Phe substitutions were identified in R strain at the IIS5 and IIS6 regions, respectively. Although the resistant Ile and Phe residues were also shared by the NS strain at the same amino acid positions, frequency of the resistant amino acid residues in the population was lower than that in the R strain. Amino acid sequences corresponding to the domain IS6 region and the linker region of the domains III-IV, which were recently shown to be involved in the pyrethroid resistance in particular lepidopteran insects, were also compared between the R and NS strains. However, no amino acid substitution was observed in the R strain at either region. These results suggest that Thr to Ile and Leu to Phe substitutions in the domain IIS4-IIS6 were associated with the pyrethroid resistance in DBM.