Abstract: In the past years,we have extensively investigated the geographic distribution of B chromosomes (Bs) in natural populations of Drosophila albomicans in China.The karyotypes of 6.738 individuals from 572 isofemale lines in 24 populations were scored.The results revealed that Bs were widely distributed in all populations except Taiwan population.The number of Bs varied from 0 to 14 in different individuals.The frequency of occurrence was the highest in Hainan population,in which 87.7 percent of the individuals contained B chromosomes.Interestingly,we found the occurrence of Bs in D.albomicans displayed a cline pattern:the frequency increased from east to west,from south to north.Furthermore,correlation was found between Bs frequency and ecological condition of habitat.In terms of this correlation,we categorized these 24 populations into 5 ecological types:1) coastal hilly land populations,2)plateau populations,3) island populations,4) mountain populations,and 5) canyon populations.