Abstract: To investigate the effects of immigration of individuals on evolution of insecticide resistance, frequencies of resistant individuals of the oriental fruit fly, Bactrocera dorsalis, to trichlorphon and β-cypermethrin were measured with different immigration rates of resistant or sensitive individuals in this study. The results showed that when resistant adults were immigrated into the susceptible population, the frequency of resistant individuals increased as the immigration rates increased. The changes in the frequency of resistant individuals to trichlorphon and β-cypermethrin were 20.04% and 41.75%, respectively, when the immigration rate of resistant individuals was 25%. Similarly, the frequency of resistant individuals decreased when increasing susceptible adults were immigrated into the resistant population. When the immigration rate of susceptible adults was 25%, the changes in the frequency of resistant individuals to trichlorphon and β-cypermethrin were 56.20% and 25.88%, respectively. The relative efficacy of influence on the changes of the frequency of resistant individuals by resistant adult immigration was the highest among all the tested populations when the immigration ratio was 5%. However, when susceptible individuals were immigrated into the resistant population, the relative efficacy of influence on the changes of the frequency of resistant individuals by trichlorphon-resistant adults and β-cypermethrin-resistant adults was the highest when the immigration ratio of sensitive individuals were 5% and 10%, respectively. The relative efficacy of influence on the changes of the frequency of resistant individuals by immigration was the highest among all the tested populations when the immigration ratio was 5%. The tendency fitting for changes of the frequency of resistant individuals and different immigration ratios indicated that resistance to trichlorphon and β-cypermethrin followed the density model and housing model, and the correlation coefficients were 0.9696 and 0.9647, respectively. The results suggest that the reasonably designing immigration rate would effectively postpone resistance development in B. dorsalis populations and meet the requirements for resistance management.

Key words: Bactrocera dorsalis, insecticide resistance, resistant individual flow, frequency of resistant individuals, trichlorphon, β-cypermethrin