Defence, Metabolism And Resistance Risk Assessment To Chlorantraniliprole In Plutella Xylostella (L.)

In order to clarify the defense, metabolism and resistance risk to chlorantraniliprole in Plutella xylostella (L.), the influence of chlorantraniliprole on protective system (CAT and POD) and the detoxifying enzymes (CarE, GST, and cytochrome P450) in P. xylostella larvae were determined by biochemical measurement at the dose of LC₂₅ and LC₅₀. A resistant strain of P. xylostella with middle level resistance to chlorantraniliprole was obtained in laboratory by leaf-dipping method. Synergism of TPP, PBO and DEM to chlorantraniliprole, cross-resistance to other insecticides in resistant strain, specific activity of detoxifying enzymes and biological parameter were determined in both resistant and susceptible strain. Resistance risk was also studied in this study. The results were as follows.The influence of chlorantraniliprole at LC₂₅ and LC₅₀ on endogenous enzymes of protective system and the detoxifying enzymes of P. xylostella larvae were determined from 6 h to 72 h by biochemical measurement. The results suggested that CAT and POD activities were inhibited by chlorantraniliprole while the activities of detoxifying enzymes were induced. Detoxifying enzymes in P. xylostella larvae treated with chlorantraniliprole were all inhibited after 6 h except CarE activity at LC₂₅ treatment. CarE activity was induced 12 h after treatment, and higher concentration could induce higher CarE activity; compared with control, it was 1.33- and 1.50- fold in LC₂₅ and LC₅₀ treatments. ODM activity was induced after 24 h treated, and high activity was induced by low concentration; Compare with control, it was 2.13- and 1.57- fold in LC₂₅ and LC₅₀ treatments. GST activity was induced after 48 h treated, and high concentration could induce high activity; Compare with control, it was 1.30- and 1.82- fold in LC₂₅ and LC₅₀ treatments.After selection for 22 generations, P. xylostella larvae, developed 25.1-fold resistance to chlorantraniliprole by leaf-dipping method. The resistance developed slowly from F0 to F10, and rapidly after F10. Cross-resistance to beta-cypermethrin, chlorfenapyr, chlorpyrifos, hexaflumuron, tebufenozide, emamectin-benzoate and spinosad was 4.27, 3.35, 3.07, 2.73, 2.25, 1.36 and 1.12- fold, respectively. The resistant strain caused cross-resistance to pyrethroid, chitinase inhibitors, ecdysone analogues, aryl-pyrrole derivatives and organophosphorus pesticides, but no cross-resistance to macrolide and its derivatives were found.The synergism of PBO, DEM, and TPP to chlorantraniliprole was significant and the synergism ratio was 15.5, 3.90 and 2.48- fold, respectively. Biochemical study showed that the specific activity of GST and CarE were 217.6μmol/ min/ mg Pr., 448.2μmol/ min/ mg Pr., which was high but not significantly in the resistance strains. The specific activity of ODM was 0.167μmol/ min/ mg Pr., significantly higher in the resistant strain than that of the susceptible strain.Relative fitness experiments for the populations of susceptible and resistance strains of P. xylostella showed that relative finesses of the resistance strain was 0.81 compared with that of the susceptible strain. Duration of eggs was shorten by about 0.5 d; shorter pupal period and longer larval period were observed; the generation time was prolonged primarily for larval duration prolonged 5 d. Male longevity was shorten by 58.2 %, but peak time of oviposition was not change while the number of eggs laid per female was significantly higher. Larval survival rate, pupation rate and emergence rate were all significantly lower than the susceptible strain. A significant decline of intrinsic rate of increase, gross reproductive rate and net reproductive rate were observed in this study.Realized heritability (h²) of resistance in different selection stages was evaluated based on the Tabashnik's methods. The results suggested that realized heritability for the entire selection experiment was 0.165. Assuming that slope was 2.0 (δp = 0.5), and h² was 0.16, it required 15 7 generations of P. xylostella to obtain 10-fold increase of chlorantraniliprole in LC₅₀ under selection pressure at 50 % 90 % mortality for each generation of selection; When h2 was 0.08, it required 31 14 generations.