Abstract: The rotation and mixture treatments of pesticides are two main strategies of pesticide application in the management of pest resistance to pesticides.The comparison of influences of the rotation and mixture treatments on the resistance evolution and the best interval period for rotation treatment of two pesticides were studied using resistance models and experiments in diamondback moth,Plutella xylostella, a “synthetic population” with 0.01 initial frequency of resistant individuals in laboratory. The simulating results on the computer indicated that the effect of rotation and mixture treatments on the resistance evolution was mainly depended on the intensity of action of pesticides,the fitness value of resistant genotype individuals and the mode of action of the mixture of the two pesticides.As for delaying the resistance evolution,the best effect could be gained under any circumstance if two pesticides were applied alternatively at every two applications. After treatments of 8 generations,the bioassay results indicated that the resistance ratio of the 3rd instar larvae to fenvalerate by the leaf dip method was 75.87 for successive treatment with fenvalerate, 28.67 for rotation treatment of fenvalerate and methylpo and 58.72 for mixture treatment of fenvalerate and methylpo.These data showed that the results from the simulation of system models had a good consistency with the bioassay results from the experimental population of the diamondback moth. It suggested that this system could be used to predict the resistance development and evaluate the resistance management strategies of pest population.

Key words: rotation treatment of pesticides, mixture treatment of pesticides, Plutella xylostella, evolution of resistance to pesticides