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By using three strains with different number of B chromosome (1-2Bs, 0B, > 2Bs) on the same genetic background, the effect of B chromosome on the reproduction of Drosophila albomicans was studied. Comparison of net reproduction and sex ratio among three strains showed that Bs has significantly effect on flies' net reproduction. The net reproduction of flies with 1-2Bs, 0B, > 2Bs is 196, 157, 147, respectively. Significant difference among three strains exists in the early stage of reproduction. The sex ratios of three strains are all close to 1:1, no significant difference was observed. The results indicated that lower dose of Bs enhances the flies' reproduction and fitness, while higher dose of Bs slightly reduces flies reproduction and fitness. These results lend the first strong support to the heterotic model.

The technique of mtDNA restriction fragments length polymorphism (RFLP) was used to survey the population structure of D. albomicans. Remarkable mtDNA polymorphism has been observed in D. albomicans populations. A total of 34 nucleomorphs were detected from 82 isofemale lines assayed by only 8 restriction enzymes. The cause and the effect of this phenomenon were discussed. As a result, it is suggested that a mechanism which maintains mtDNA diversity exists in this fly, and that the high intra-populational polymorphism could numerically conceal the extent of differentiation between populations. In addition, on the base of restriction maps, it was found that the mtDNA molecule of D. albomicans might be impacted by the selection pressure during its evolution process both on the nucleotide composition and on the functional regions.