Cytoplasmic Incompatibility within and Between Culex Molestus and Cx. Quinquefasciatus (Diptera: Culicidae)1

Abstract

Two members of the Culex pipiens complex of mosquitoes, Cx. quinquefasciatus and Cx. molestus, were treated as separate species in an investigation of cytoplasmic incompatibility between recently colonized geographical strains. Unidirectional incompatibility, semicompatibility or subfertility was found when females from Perth, Australia, were crossed with males originating from a warmer climate. Intertaxic crosses gave results similar to intrataxic crosses. Backcrosses to replace the quinquefasciatus genome with that of molestus over 9 generations produced a slight breakdown in incompatibility in the F₂ to F₄ backcross generations only. The results are interpreted as indicating that the phenomenon of cytoplasmic incompatibility is independent of species gene pools. A theory is proposed that a host-mediated environmental factor may act on the rickettsialike symbionts to produce different microbial strains in the different crossing types of the mosquito host.