The present study was designed to obtain detail information on the relationship between the populations of different virulence and biotype formation oX BPH led on IR26 variety with Bphl resistant gene. It seemed that a distinct difference of individual virulence existed in the laboratory population,especially in resistant varieties IR26 and ASD7. The results showed that the different populations, of which the virulence was determined by the amount of honeydew excreted on IR26, had no significant difference in the degree of their adaptation to TR26 under the selection pressure. Using the seedling bulk test and the population build-up experiment, the 3 selected insect populations reared on IR26 in 10th generation were able to kill IR26 and adapted to these host plants but could't survive well on Mudgo variety with Bphl gene. In addition, the amount of honeydew excretion, survival and adult weight on IR26 increased during the selection process, the shift in the insect populations to a more virulent biotype was also confirmed by these tests.