Abstract: To investigate the effects of high temperature on biological fitness and evolution of insecticide resistance, the life-table parameters and susceptibility to avermectin in the progenies of insecticide-resistant and -susceptible populations of Plutella xylostella were studied. The results showed that both resistant and susceptible populations displayed significantly lower development duration （D）, net reproduction rate （R₀）, innate rate of increase （r_m）, finite rate of increase （λ）, total fecundity number, average longevity of female adult, daily fecundity number and hatchability at 33.5℃ as compared to those at 25℃. There were no significant differences in r_m, λ, D and daily fecundity number between resistant population and susceptible population. although R₀ of resistant population was slightly lower than that of susceptible population at 25℃（87% of the susceptible population）. However, compared to the susceptible population, the resistant population had significantly lower R₀ （75% of the susceptible population）, r_m （64% of the susceptible population）, average longevity of female, total fecundity number and hatchability at 33.5℃. The avermevtin resistance declined greatly in the progenies of resistant population after the insects were reared at 33.5℃ for one generation. However, no great decrease of avermectin resistance was found in the progenies of susceptible population under the same treatment condition. The results suggest that the biological fitness of resistant population was eventually lower than that of susceptible population at both high and normal temperatures. In particular, the fitness of resistant population was far lower than that of susceptible population under high temperature condition. Significantly lower biological fitness of resistant population under heat stress might result in the sharp decline of avermectin resistance in the progenies of resistant population when the insects were reared at 33.5℃ for one generation.

Key words: Plutella xylostella, insecticide, resistant population, susceptible population, high temperature, life table, biological fitness