Using the eminent toolkit of Wolbachia to study Culex pipiens populations and their relations in Europe

Abstract: Culex pipiens, in the family Culicidae, has emerged as one of the biggest vectors for West Nile virus. It has two bioforms, pipiens and molestus, which differ from each other regarding habitat, diapause, and prey. Pipiens prefers to bite birds, and molestus prefers to bite humans. There is to some extent hybridization between the two, which creates a bridge-vector between birds and humans. One way to study the relationships and spreading of the mosquitos is using the intracellular bacteria Wolbachia pipientis which is present in at least 99% of al Culex mosquitoes. The bacteria have two fast evolving genes, pk1 and ank2 which are suitable for this. Not only are the bacteria suitable for genetics, but it is also manipulating the reproductive system of the mosquitoes through Cytoplasmic Incompatibility, which changes structures of populations and allows for the bacteria to spread fast and efficient. We wanted to investigate levels of Wolbachia in different populations, as well as if the two bioforms prefer a prey, together with mapping the relationships between populations using the two genes. We found that Wolbachia was present in all tested mosquitoes, with higher levels of it in the abdomen than in the thorax. We also found that the theory of a preferred prey was false within the tested populations, since both bioforms preferred birds. Lastly, we could identify five different strains of Wolbachia pipientis concentrated to different locations. This study has shown that Wolbachia is present in all tested mosquitoes and is a useful tool to determine relationships within and between populations. This is important to be able to gain understanding of the spread of West Nile virus and other vector borne diseases spread by Culex pipiens mosquitoes.