Hibernation site patterns and survival rates of adult overwintering mosquitoes in Central Europe

Abstract text

Adult overwintering mosquitoes can act as reservoir for viruses (e.g. West Nile virus) and thus may contribute to the establishment of mosquito-borne viruses in Central Europe. Knowledge on the ecology of adult overwintering mosquitoes can enhance our understanding of the mosquito population development after winter and how arboviruses persist in temperate regions. Here, we present three studies analysing mosquitoes" preferred hibernation sites and the factors influencing the winter survival in these hibernation sites. In the first study, we quantified the number of adult overwintering mosquitoes in cellars and aboveground structures such as sheds or barns. In 2016/17 and 2018/19, we searched for overwintering mosquitoes in 149 different constructions in Northwest Germany. Over both winters, 2,716 mosquitoes were collected; mosquitoes were detected in 44% of the cellars and 33% of the aboveground constructions. Culex p. pipiens Linnaeus, 1758 was the dominant species in cellars, while high numbers of Anopheles messeae Falleroni, 1926 were detected in a single barn. Only nine Culex torrentium Martini, 1925 specimens were detected, although collection data from summer would suggest that the species is highly abundant. In 2022, a second study was conducted in Poznań, Poland, where we collected overwintering mosquitoes from animal burrows and spatially close man-made constructions. In total, we detected 5,511 Culex specimens (man-made sites: 3,823, animal burrows: 1,688). While Cx. p. pipiens was again the most abundant species at the man-made hibernation sites (~90%), Cx. torrentium predominated in the animal burrows (~75%). The third study aimed to analyse the survival rates in dependence of the environmental conditions at different hibernation sites. Field-sampled overwintering Cx. p. pipiens and An. messeae were divided into groups and placed in cages at different cellars and sheds, where temperature and relative humidity was logged hourly. Mosquito wing size, lipid content and mortality rates were measured. Increasing mean temperatures at the hibernation sites (5 °C to 16 °C) but not mean relative humidity (58% to 94%) were correlated to the winter mortality rates of the mosquitoes. Larger specimens store more lipids, and in Cx. p pipiens, but not in An. messeae, survival probability of large specimens was significantly higher.