Molecular discrimination of Wolbachia in the Culex pipiens complex: evidence for variable bacteriophage hyperparasitism.

The medically important members of the Culex pipiens species complex provide an enigma for systematists, evolutionary biologists, and vector biologists. The species complex is composed of forms that differ in their ecology, behaviour, physiology and vector competence. Cytoplasmic incompatibility (CI) caused by endosymbiotic Wolbachia bacteria is thought to play an important role in restricting gene flow and the evolution of the Culex complex. Here we describe the first molecular marker useful for discriminating between Wolbachia infections in Culex. A putative bacteriophage locus (orf7) varies between Culex forms in copy number and sequence. We provide evidence that the orf7 loci are strictly associated with Wolbachia and are maternally inherited.