Resistance to Diamide Insecticides in Plutella xylostella (Lepidoptera: Plutellidae): Comparison Between Lab-Selected Strains and Field-Collected Populations

Diamondback moth, Plutella xylostella (L.; Lepidoptera: Plutellidae), is an important pest of crucifers worldwide. The extensive use of diamide insecticides has led to P. xylostella resistance and this presents a serious threat to vegetable production. We selected chlorantraniliprole (R-f) and flubendiamide (R-h) resistance strains of P. xylostella with resistance ratios of 684.54-fold and 677.25-fold, respectively. The R-f and R-h strains underwent 46 and 36 generations of lab-selection for resistance, respectively. Low cross resistance of R-h to cyantraniliprole was found. Cross resistance to chlorfenapyr, tebufenozid, and indoxacarb was not found in R-f and R-h strains. The P. xylostella ryanodine receptor gene (PxRyR) transcripts level in the R-f and R-h strains was up-regulated. Except for R-f34 and R-h36, PxRyR expression in all generations of R-f and R-h selection gradually increased with increasing resistance. Two resistant populations were field-collected from Guangzhou Baiyun (R-b) and Zengcheng (R-z) and propagated for several generations without exposure to any pesticide had higher PxRyR expression than the susceptible strain (S). In the S strain, PxRyR expression was not related to the resistance ratio. Gene sequencing found that the RyR 4946 gene site was glycine (G) in the S, R-f, and R-h strains, and was glutamate (E) with 70% and 80% frequency in the R-b and R-z populations, respectively. The 4946 gene site was substituted by valine (V) with the frequency of 30% and 20% in R-b and R-z populations, respectively. These results increase the understanding of the mechanisms of diamide insecticide resistance in P. xylostella.