Abstract
The Culex pipiens complex encompasses five species and subspecies of the genus Culex. Over time, a multitude of morphologically indistinguishable species has been assigned to this complex with several species being classified as important vectors for different diseases. Some species of this complex hibernate in subterranean habitats, and it has been proven that viruses can survive this phase of hibernation. However, studies focusing on the environmental requirements, ecology and spatial and temporal distribution patterns of mosquitos in underground habitats are sparse. Here, we investigate the main environmental factors and dependencies of Culex, considering the number of individuals and survival probabilities in underground habitats during the winter months. Methods. Since the State of Hesse, Germany harbors about 3500 to 4000 subterranean shelters ample availability of subterranean habitats there provides a good opportunity to conduct detailed investigations of the Culex pipiens complex. In this study, we identified a sample of 727 specimens of overwintering females within the Culex pipiens complex from 52 different underground sites collected over a period of 23 years using qPCR. A complete data set of samplings of hibernating mosquitos from 698 subterranean habitats in Central Germany over the same period was available to study the spatial and temporal patterns and the effect of temperature and precipitation conditions on these hibernating populations using a generalized linear model (GLM). Results. Our qPCR-results show, similar to aboveground studies of mosquitos, that Culex pipiens pipiens and Culex torrentium occur sympatrically. On the other hand, Culex pipiens molestus occurred very rarely. The GLM revealed no shifts in species composition over time, but different preferences for subterranean hibernacula, chemical effects on overwintering populations as well as effects of annual and seasonal mean temperature and precipitation during the active phase from March to November. Cx. p. pipiens and Cx. torrentium are the most common species within Hessian caves and other underground habitats during winter. They co-occur with different frequency without any patterns in species composition. Weather conditions influence the number of overwintering mosquitos during the activity phase. Depending on cave parameters, the number of mosquitos decreases during the winter months.
Highlights
Culicidae members belonging to the Culex pipiens complex are difficult to distinguish morphologically
Since Cx. p. pipiens is o rnithophilic[15,16], it plays a major role in the transmission of West Nile Virus (WNV) within wild bird populations, except in the northern Central and Mid-Atlantic United States, where it shows higher than usual affinity for humans and becomes a bridge v ector17. Andreadis[17] attributes this alteration of host preference to potential genetic ancestry with Cx. p. molestus and is considered analogous to the assumed h ybridization[18]
P. pipiens and Cx. torrentium in most of the cavernous habitats while there were no clear differences in species composition when comparing different sampling years
Summary
Culicidae members belonging to the Culex pipiens complex are difficult to distinguish morphologically. Like many other mosquito species, members of the Culex pipiens complex transmit different arthropodborne viruses (arboviruses). Several studies show that Culex species are competent vectors[13,14,15] This may be true for Cx. torrentium which is widely distributed in Central E urope[13,14]. Considering the still unresolved structure of the Culex pipiens complex as well as the variability in their biological interactions and lack of knowledge within Germany, this is the first study to include hibernating mosquitos on a larger scale. Hesse is suited to study the population structure and hibernation preferences of Culex due to its many subterranean habitats, the wide-ranging distribution of various Culex species and the temperate Central European climate in this region of Germany
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