Biotype dynamics of the common house mosquito Culex pipiens in the anthropogenic environment in winter: a citizen science approach

Abstract The two biotypes of the mosquito species Culex pipiens s.s. (biotype pipiens and biotype molestus ) differ in overwintering strategy. Biotype pipiens enters diapause, whereas biotype molestus remains active year-round. In the Netherlands, flooded crawlspaces may provide sheltered development sites for biotype molestus in winter. We therefore investigated the effects of human population density and crawlspace flooding on the presence of Cx. pipiens s.s. biotypes and their hybrids using citizen-submitted mosquito samples via the platform ‘Muggenradar.’ Mosquitoes were categorized by population density and crawlspace condition. In addition, biotypes and feeding patterns were identified using molecular analyses. Descriptive analyses indicated that biotype molestus was more abundant in areas with high population density (24.1% at ’low’ versus 58.6% at ‘high’), while biotype pipiens dominated in areas of low population density (19.5% at ‘high’ versus 63.3% at ‘low’). Similarly, we found an association of biotype molestus with flooded crawlspaces (68.4% of specimens). However, these patterns were not fully supported by a multivariate analysis. Blood meal analyses revealed that nearly all biotype molestus (98.2%) and hybrid mosquitoes (100%) fed on humans. Surprisingly, six blood-engorged biotype pipiens were collected. We conclude that anthropogenic environments may influence the occurrence of Cx. pipiens s.s. biotypes and hybrids in winter.