title: Winter Activity and Aboveground Hybridization Between the Two Biotypes of the West Nile Virus Vector Culex pipiens.
abstract: Culex (Cx.) pipiens mosquitoes are important vectors of West Nile virus (WNV). In Europe, the species Cx. pipiens consists of two biotypes, pipiens and molestus, which are morphologically identical, but differ in behavior. Typical behavior of the molestus biotype is the ability to remain active during winter, whereas the pipiens biotype enters diapause. The current paradigm is that the two biotypes occur sympatrically in southern Europe, but occur in isolated above- and belowground populations in northern Europe. In northern Europe, hybridization between biotypes is considered to be low because of the barrier that exists between typical habitats. Data on the occurrence of the biotypes and hybrids in northern Europe, however, are scarce, because identification to the level of biotype is often not performed. Our objective was to clarify the distribution of the Cx. pipiens biotypes and to determine hybridization rates in The Netherlands. Cx. pipiens mosquitoes were collected using three different approaches. First, traps were deployed randomly throughout The Netherlands during the summers of 2011 and 2012 (active surveillance). Second, using a web-based reporting platform and media campaign, Dutch citizens were asked to send dead mosquitoes to our laboratory during the winter and summer of 2014 (passive surveillance). Third, larvae and adults were collected during the summer of 2014 from aboveground locations in Amsterdam to identify molestus larval habitats. Real-time PCR was used for identification to the level of biotype. We found that biotype molestus and hybrids were feeding indoors during winter and summer in The Netherlands and that hybridization rates ranged between 6% and 15%. Larval habitats of biotype molestus were found to occur aboveground. The high percentage of hybridization has implications for assessing the risk of WNV transmission, because hybrids are thought to have ideal characteristics for bridging WNV between birds and humans.
authors.affiliation: 1 Laboratory of Entomology, Wageningen University and Research Centre , Wageningen, The Netherlands .
authors.forename: Chantal B F
authors.initials: CB
authors.lastname: Vogels
authors.affiliation: 1 Laboratory of Entomology, Wageningen University and Research Centre , Wageningen, The Netherlands .
authors.forename: Lennart J J
authors.initials: LJ
authors.lastname: van de Peppel
authors.affiliation: 2 Environmental Systems Analysis Group, Wageningen University and Research Centre , Wageningen, The Netherlands .
authors.forename: Arnold J H
authors.initials: AJ
authors.lastname: van Vliet
authors.affiliation: 3 Dutch National Plant Protection Organization , Wageningen, The Netherlands .
authors.forename: Marcel
authors.initials: M
authors.lastname: Westenberg
authors.affiliation: 4 Centre for Monitoring of Vectors (CMV), National Reference Centre (NRC) , Netherlands Food and Consumer Product Safety Authority (NVWA), Ministry of Economic Affairs, Wageningen, The Netherlands .
authors.forename: Adolfo
authors.initials: A
authors.lastname: Ibañez-Justicia
authors.affiliation: 4 Centre for Monitoring of Vectors (CMV), National Reference Centre (NRC) , Netherlands Food and Consumer Product Safety Authority (NVWA), Ministry of Economic Affairs, Wageningen, The Netherlands .
authors.forename: Arjan
authors.initials: A
authors.lastname: Stroo
authors.affiliation: 5 Public Health Service Amsterdam , Amsterdam, The Netherlands .
authors.forename: Jan A
authors.initials: JA
authors.lastname: Buijs
authors.affiliation: 1 Laboratory of Entomology, Wageningen University and Research Centre , Wageningen, The Netherlands .
authors.forename: Tessa M
authors.initials: TM
authors.lastname: Visser
authors.affiliation: 1 Laboratory of Entomology, Wageningen University and Research Centre , Wageningen, The Netherlands .
authors.forename: Constantianus J M
authors.initials: CJ
authors.lastname: Koenraadt
mesh_terms: D000818:Animals; D003465:Culex / Q000235:genetics / Q000502:physiology* / Q000821:virology; D017753:Ecosystem; D005060:Europe / Q000453:epidemiology; D005260:Female; D006801:Humans; D006824:Hybridization, Genetic; D007303:Insect Vectors / Q000235:genetics / Q000502:physiology* / Q000821:virology; D007814:Larva; D008297:Male; D009426:Netherlands / Q000453:epidemiology; D011159:Population Surveillance; D012621:Seasons; D014901:West Nile Fever / Q000453:epidemiology*; D014902:West Nile virus / Q000302:isolation & purification*
keywords: Active surveillance; Culex torrentium; Distribution; Europe; Passive surveillance; The Netherlands; molestus; pipiens