Sympatric occurrence of Culex pipiens (Diptera, Culicidae) biotypes pipiens, molestus and their hybrids in Portugal, Western Europe: feeding patterns and habitat determinants

Abstract

Culex (Culex) pipiens (Diptera: Culicidae) has two recognized biotypes, pipiens and molestus, which differ in physiology and behaviour; this difference may influence vectorial capacity for West Nile virus (WNV). Our goal was first to determine the presence of Cx. pipiens populations in 31 locations in Portugal and to subsequently analyse their host-feeding preferences and habitat determinants. Molecular identification of Cx. pipiens forms and their hybrids was performed in 97 females; bloodmeal sources were identified in 59 engorged specimens. Overall, 61.9% of specimens were identified as Cx. pipiens f. pipiens, 20.6% as Cx. pipiens f. molestus, and 17.5% as hybrid forms. Culex pipiens f. pipiens fed preferentially on birds, and Cx. pipiens f. molestus on humans. Hybrid forms fed mostly on birds, but human bloodmeals were common. With reference to habitat, Cx. pipiens f. pipiens and hybrid forms were positively correlated with peri-urban habitats. Our results confirm the sympatric presence of different Cx. pipiens biotypes in 14 of the 31 locations studied. Peri-urban areas were a common habitat of all biotypes and may represent zones of hybridization. The feeding preferences and sympatric distribution of the Cx. pipiens biotypes observed in Portugal favour the epizootic circulation of WNV and the occurrence of disease outbreaks of WNV.

The role of Culex pipiens mosquitoes in transmission of West Nile virus in Europe

“…pipiens biotypes and hybrids in aboveground habitats throughout Europe. These results are in line with previous findings from The Netherlands , Germany (Rudolf et al 2013), Austria (Zittra et al 2016), Portugal (Gomes et al 2009, Osório et al 2014), Italy (Di Luca et al 2016, and Greece (Gomes et al 2013a). There was a clear gradient of decreasing biotype pipiens and increasing biotype molestus proportions from northern to southern latitudes.…”

“…Hybrids of the two biotypes were described from The Netherlands in 2010, but they were exclusively reported from the underground transit system of Amsterdam (Reusken et al 2010a). In the present nationwide study, we found that biotypes pipiens and molestus both occur aboveground (in mosquito traps, as well as inside houses of Dutch citizens), as is the case in southern European countries, with comparable hybridization rates ranging between 5-15 % (Amraoui et al 2012, Gomes et al 2013a, Gomes et al 2009, Osório et al 2014). …”

“…These laboratory findings are supported by field studies carried out in northern Europe, which reported serological evidence of WNV in sentinel chickens, resident birds, and migratory birds in the United Kingdom (Buckley et al 2006, Buckley et al 2003, and in migratory birds in Germany (Linke et al 2007). This evidence may suggest that WNV is already circulating among birds Introduction 1 they have a relatively high infection prevalence in the field (Engler et al 2013, Hayes et al 2005, strong preference to feed on bird hosts (Fritz et al 2015, Hamer et al 2009, Osório et al 2014, and high abundance during summer (Chaskopoulou et al 2016, Spielman 2001, which together makes Cx. pipiens a potentially important contributor to WNV transmission (Kilpatrick et al 2005).…”

“…Host availability can induce a strong shift in host feeding behaviour of biotype molestus from mammals to birds, especially in areas with high bird densities (Gomes et al 2013b). Previously, biotype molestus has been described as occurring underground , but recent studies show that both biotypes occur sympatrically in aboveground habitats throughout Europe (Di Luca et al 2016, Osório et al 2014, Rudolf et al 2013. Furthermore, biotype pipiens and biotype molestus can form hybrids which show intermediate host preference (Fritz et al 2015).…”

“…Thus far, in-depth studies that differentiated between the biotypes were done at country level (Di Luca et al 2016, Gomes et al 2013a, Osório et al 2014, Rudolf et al 2013, Zittra et al 2016. Few of these studies systematically compared biotype ratios among different habitat types (Di Luca et al 2016, Osório et al 2014, Zittra et al 2016). However, due to differences in experimental design it is hard to make direct comparisons between Cx.…”