Abstract: In order to understand the inviability of hybrid F₁ eggs and the relationship of this to Wolbachia infection in the Culex pipiens complex in China, the crossing experiments of 4 subspecies of the complex without and with tetracycline treatment were performed. The results revealed there was unidirectional cytoplasmic incompatibility (CI) between Cx. Pipiens molestus males and females of the other 3 subspecies in the complex without tetracycline treatment, and the hatching rates of eggs from matings between the males of Cx. Pipiens molestus and the females of Cx. Pipiens pipiens, Cx. Pipiens quinquefasciatus and Cx. Pipiens pallens were 0.06%，0.46% and 0.19%, respectively. Treatment with tetracycline resulted in the elimination of CI. F₃ hatching rates after tetracycline treatment between the males of Cx. Pipiens molestus and the females of Cx. Pipiens pipiens, Cx. Pipiens quinquefasciatus and Cx. Pipiens pallens were 89.49%（t=3.90×10²⁸＜t_0.01=2.704），23.39%（t=9.15×10⁷＜t_0.01=2.660）and 22.27%（t=5.08×10⁴＜t_0.01=2.750）, respectively. However, treatment with tetracycline resulted in the occurrence of new kinds of CI.

Key words: Culex pipiens complex, hybridization, cytoplasmic incompatibility, Wolbachia