Insecticide resistance in Plutella xylostella (Linnaeus) (Lepidoptera: Plutellidae) is a major constraint on the global production of cruciferous crops. For effective management of insecticide resistance, it is necessary to develop a molecular detection tool for predicting insecticide resistance levels based on the mutation frequency of target sites. In this study, a susceptible strain (SHggt) of P. xylostella was subjected to chlorantraniliprole and tetraniliprole selection under laboratory conditions to obtain the CHLSel and TETSel strains, respectively, to determine their resistance development, cross-resistance and mutation frequencies of the P. xylostella ryanodine receptor (PxRyR). In addition, the tetraniliprole resistance and the mutation frequencies of the PxRyR from 7 field populations were evaluated. Continuous selection over 30 generations resulted in resistance ratios (RRs) of 7,073.2-fold and 6,971.0-fold for the CHLSel and TETSel strains, respectively, and thousandfold increases in cross-resistance to unexposed diamides, e.g., cyantraniliprole and flubendiamide, were observed. For the field populations, three out of seven populations have developed more than thousandfold resistance to tetraniliprole. Among the three investigated target site mutations in PxRyR, only I4790K was detected in both laboratory-selected strains. However, 2 mutations, I4790K and G4946E, were detected in field populations. A positive correlation between RRs and K allele frequencies was observed in the laboratory-selected/relaxed strains and field populations of P. xylostella. These results suggest a possible link between the development of anthranilic diamide resistance and the frequency of the PxRyR I4790K mutation, which can be used to develop effective strategies for diamide resistance management in P. xylostella.
Graphical Abstract
The I4790K mutation plays a key role in anthranilic diamide resistance in P. xylostella. The K allele frequency increased when the resistance ratio (RR) increased but decreased when the selection pressure was removed and when the RR decreased. A positive correlation between resistance ratios and K allele frequencies was observed in the laboratory-selected and relaxed strains and field populations. This correlation could be used for the rapid prediction of diamide resistance levels in field populations of P. xylostella.
