The wide application of chlorantraniliprole, which selectively targets insect ryanodine receptors (RyR), for control of the diamondback moth, Plutella xylostell

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.

The diamondback moth (DBM), Plutella xylostella L., is an important pest of cruciferous vegetables, and population control mainly depends on chemical pesticides. Emamectin benzoate is a highly effective insecticide used for controlling DBM. However, it is unknown how the sublethal effects of low concentration residues of emamectin benzoate on DBM. So the population development sublethal effects of emamectin benzoate, at LC₅, LC₁₀, and LC₂₀ with concentrations of 0.014 mg/L, 0.024 mg/L and 0.047 mg/L, respectively, on adult DBM and their progeny were investigated in this study. The pupal weight, pupal period, female fecundity, and vitellin content of the F₀ DBM generation increased significantly compared to the control. And the single female oviposition number of DBM was increased by 20.21% with LC₂₀ treatment. The pupation rate, adult longevity and ovariole length of the treatment groups decreased significantly. The fecundity of DBM in the treatment groups increased, and this increased the population by a presumptive 13.84%. Treatment also led to the shortening of ovarioles and the reduction of egg hatching, and increased pupal weight in the F₁ generation. We concluded that the effects of sublethal/low concentration emamectin benzoate on the different life stages of DBM were variable, and the reproductive hormesis on DBM adults were attractive findings.