Culex pipiens sensu lato has been documented as West Nile virus (WNV) vector in southeastern Romania. Bucharest, the densely populated capital city of Romania, and the surrounding Ilfov county are WNV hotspots. In this area, the morphologically indistinguishable biotypes of Cx. pipiens, namely pipiens and molestus, are usually differentiated by their behavioral and physiological traits. Their involvement in WNV transmission, as suggested by entomological investigations, was not previously documented for each biotype. We used a Real-Time PCR assay based on CQ11 microsatellite to identify the Cx. pipiens biotypes and their hybrids collected in various habitats in the Bucharest metropolitan area. A sympatric distribution of both biotypes was observed, with a preference of green areas for pipiens, and human settings and animal farmlands for molestus. In the latter habitats, pipiens and molestus were found in mixed aboveground populations. A low number of hybrids was found suggesting existence of reproductive isolation. In subway tunnels molestus was dominant with a higher number of hybrids recorded than aboveground. Blood-engorged mosquitoes were identified to biotype and the blood meal source identified by DNA barcoding. Overall, Cx. pipiens s.l. fed mainly on birds, commonly on house sparrows, collared doves, and blackbirds, which are potential WNV-amplifying hosts. The preference for avian hosts was expressed strongest by pipiens biotype, while molestus was substantially less specific, feeding on avian and mammal hosts with similar frequency, with humans representing 20% of the hosts. Hybrids had a host choice closer to that of molestus. These findings highlight the role of pipiens biotype as enzootic/epizootic vector, and specifically show molestus as the bridge vector for WNV. The pipiens and molestus biotypes show important differences in habitat preferences, including oviposition; these findings demonstrate that targeted mosquito control to limit WNV transmission may be possible.
Keywords: Culex pipiens s.l.; biotype identification; blood meal analysis; hybrids; sympatric distribution.