European Populations Carry Different Strains of .

The mosquito occurs in two ecotypes differing in their mating and overwintering behavior: pipiens mate in open environments and diapause, and molestus also mate in small spaces and is active throughout the year. carry endosymbionts of the Pip strain, but the frequency of infection differs between studied populations. infection affects the host reproductive success through cytoplasmic incompatibility. Pip is divided into five types, Pip I-V. The type of Pip carried varies among populations. In northern European locations different Pip types are found in the two ecotypes, whereas in southern locations, they often carry the same type, indicating differences in hybridization between ecotypes. In this study, specimens of both ecotypes were collected from Sweden and compared to specimens from Norway, England, Italy, and the Netherlands, as well as from Mali and Thailand. The abundance varied, but all specimens were infected by , while the tested specimens of other mosquito species were often uninfected. The Pip strains were determined through the sequence analysis of genes and , showing that ecotypes in Scandinavia carry different Pip strains. The observed differences in Pip strains indicate that hybridization is not frequent and may contribute to barriers against hybridization of the ecotypes in Sweden and Norway.