The Study On Genetics Of Chlorfenapyr Resistance In Plutella Xylostella

The genetics of resistance to chlorfenapyr were carried out on susceptible laboratory strains and resistant strains (2368.91 X ) of diamondback moth, Plutella xylostella. The LD50 and probit regression lines of susceptible and resistant parents and their F1 hybrids, F1-backcross progeny and F2-masscross progeny were assessed in order to determine inheritance character. The result showed that the degree of dominance of FRS and FSR were 0.5517 and 0.5402 respectively. It suggested that the resistance of diamondback moth to chlorfenapyr was autosomal, incompletely dominant and probably polygenic control. The resistance gene frequency decreased significantly.The research was taken to two different 'strains in the terms of developmental and reproducetive characterstics under artifitial climate condition. Life tables of the resistant strain and the susceptible strain were constructed. The results indicated that the resistant strain possessed some developmental disadvantage including prolonged larva duration, and reproductive disadvantage including lower mean number of eggs per female. The intrinsic rate of natural increase in the resistant and susceptible strain calculated by establishing life table were 25.2 and 55.4, respectively. Rate of relative fitness of resistant strain was 0.45 based on comparing with that of susceptible strain.The resistance ratios (RR) of Plutella xylostella declined when the resistant strain was reared on fresh cabbage leaves in the laboratory. From F1 to F3, resistance reversion rate was slow. From F4 to F6, resistance reversion rate was fast relatively. From F7 to F9, there was a tendency for declining slowly once again. After 9 generation, the resistance ratios were over 7-8 folds from 2368.91 folds to 305.38 folds.Great difference was found between the two strains in rate of respiration after treated by insecticide chlorfenapyr, the resistant strain showed little variation treated by insecticide, but the susceptible strain showed great decrease treated by insecticide. The difference of F1 hybrids and F2-masscross progeny treated varied between those of the resistant strain and susceptible strain, backcross progeny while the difference of treated by insecticide was greater than those of F1 and F2. So it was estimated that the variation of respiration rate was related to resistance reversion.The activity of 3 enzymes (esterase, carboxylesterase and glutathione-S-transferase)from two strains were determined. The results showed that the activity of esterase and carboxylesterase of the resistant strain has no distinct difference compared with those of the susceptible strain, and those of F1 hybrids, F2 and BC were all lower than those of the susceptible strain and there were not any regularities.The activity of glutathione-S-transferase of the resistant strain was lower than that of the susceptible strain, was 0.5775-fold compared with the susceptible strain, while that of other strains between that of the resistant strain and susceptible strain and greater than that of the resistant strain. The results indicated that the glutathione-S-transferase contributed to resistance of diamondback moth to Chlorfenapyr.The esterase of hemolymph of the diamondback moth was analysed by polyacrylamide gelelectrophoresis (PAGE). In contrast to the susceptible strain, there was a special enzyme band in the resistant strain, the results indicated that perhaps there was a new enzymes.