The study, conducted between April and September 2019, represents a significant advance for a country where mosquito research has historically been uneven. After the eradication of endemic malaria in the 1930s, public interest in Swiss mosquitoes waned considerably. Only in recent years, driven by the spread of invasive mosquito species, multiple outbreaks of mosquito-borne diseases in neighboring countries, and the first detection of West Nile virus in Swiss mosquitoes in 2022, has the urgency of understanding regional mosquito distribution become apparent. Currently, 41 mosquito species have been recorded in Switzerland, but detailed knowledge outside the southern region remains scarce or outdated.

Researchers deployed CDC miniature light traps baited with carbon dioxide from dry ice pellets at 15 sampling sites, hanging them approximately 1.5 meters above the ground to capture blood-seeking female mosquitoes. Traps ran for 24 hours during six monthly collection rounds. In parallel, the team surveyed larval habitats using standard pint dippers, examining ponds, ditches, and other accessible standing water bodies near each adult trapping site. During July and August, the peak season for container-breeding invasive species, additional larval sampling targeted garden pots, birdbaths, and other artificial containers at peri-urban and urban locations.

The 15 sites spanned three environment categories: eight in entirely natural settings within the nature reserves, six near residential zones classified as peri-urban, and one urban site within the city of Yverdon-les-Bains, home to roughly 30,000 people at the southern edge of the study area. This design allowed the researchers to compare mosquito communities across a gradient from pristine wetland to human-altered landscape, testing whether mosquitoes breeding in the reserves spill over into nearby settlements.

Over the six sampling rounds, the team collected 3,674 mosquito specimens, comprising 3,422 adult females from the CDC traps and 252 larvae from habitat surveys. Identification relied on morphological keys for female adults and third and fourth instar larvae, with several closely related species grouped where morphological differentiation alone was impossible. These groups included the Aedes annulipes-cantans pair, the Aedes cinereus-geminus pair, the Culex pipiens-torrentium complex, and the Anopheles claviger-petragnani group. Molecular methods were not applied in this study.

Five species dominated the adult catch, together accounting for 86.21 percent of all specimens: Aedes annulipes-cantans, Aedes vexans, Aedes sticticus, Aedes cinereus-geminus, and Aedes rusticus. This composition is typical for a wetland area, where floodwater species that deposit eggs in humid soil thrive when spring and early summer flooding creates ideal breeding conditions. The alluvial forest at Chablais de Cudrefin, flooded each spring by a beaver-regulated stream, proved particularly productive for Aedes vexans and Aedes sticticus, whose eggs can survive at least five years in dry soil before hatching when flooding coincides with temperatures exceeding 9 degrees Celsius.

Seasonal dynamics followed clear patterns. In April, adult abundance remained very low while larval numbers peaked, dominated by early-season species such as Aedes annulipes-cantans and Aedes rusticus, whose eggs hatch when water temperatures reach 6 to 8 degrees Celsius. Adult catches surged in mid-June, with more than three times as many adults collected compared to July. The emergence of the floodwater species Aedes vexans and Aedes sticticus in mid-June coincided with two episodes of rising water levels in Lake Neuchâtel, likely triggered by heavy precipitation. Less abundant species generally peaked later in the season.

Comparing habitat types revealed a striking overlap in species composition across natural, peri-urban, and urban environments, though diversity metrics told a more nuanced story. The Shannon-Wiener diversity index reached 1.637 in natural environments compared to just 0.811 in combined peri-urban and urban sites, indicating that mosquito communities in pristine wetlands are both richer and more evenly distributed. Adult catches per site were generally higher in nature areas, averaging 327 specimens per site versus 115 in peri-urban and urban locations combined. Interestingly, larval abundance was slightly higher in peri-urban sites, though this result was largely driven by two highly productive locations.

Notably, no invasive mosquito species were detected anywhere in the study area. The Asian tiger mosquito Aedes albopictus, an established urban pest in southern Switzerland capable of transmitting at least 26 arboviruses, was absent. So too were the Asian bush mosquito Aedes japonicus, which is widespread in Switzerland and has been detected close to the study area, and the Korean mosquito Aedes koreicus, currently restricted to a few Swiss regions. This absence is reassuring but not a reason for complacency, as native mosquitoes can also transmit pathogens.

The recent detection of West Nile virus in Culex pipiens mosquitoes in southern Switzerland, together with rising numbers of human infections across Europe, underscores the potential risk of local transmission. Culex pipiens form pipiens is considered the main vector for West Nile virus, while form molestus functions as a bridge vector facilitating virus movement from birds to humans and horses. Given that the Grande Cariçaie hosts both migratory birds and Culex pipiens-torrentium mosquitoes, the researchers argue that future monitoring for West Nile virus should be considered to assess public and veterinary health risks in the region.

Beyond disease surveillance, the study highlights the conservation value of the Grande Cariçaie as a hotspot of mosquito diversity. The 17 species recorded represent 41 percent of all mosquito species reported in Switzerland, a remarkably high proportion for a local-scale survey. This diversity is comparable to other well-studied Swiss wetlands, including the Bolle di Magadino nature reserve with 18 species and the Langholz wetland reserve with 17. In an alpine country where mountain barriers create distinct climatic zones, knowledge gained from one region cannot simply be extrapolated to another, making such regional inventories essential building blocks for a national picture.

The researchers acknowledge methodological limitations that shaped their results. Culex hortensis and Culex territans were found only as larvae, likely because these species feed primarily on reptiles, amphibians, and birds and are therefore less attracted to carbon dioxide-baited traps. The abundance of ornithophilic Culex species may also have been underestimated due to trap placement at 1.5 meters above ground, a height optimized for capturing human-biting species rather than bird-associated ones. Coquillettidia richiardii larvae, which attach to aquatic plants via their siphons, cannot be sampled with standard dipping techniques, meaning only adults of this species could be detected.

As Europe faces increasing emergence of mosquito-borne viruses, continued surveillance of mosquito diversity in Switzerland remains essential. This first comprehensive inventory of the Grande Cariçaie provides a valuable baseline for future monitoring, enables meaningful comparisons with other Swiss regions, and enhances understanding of mosquito ecology north of the Alps. Whether the aggressive human biters that dominate the wetland’s fauna will increasingly interact with nearby settlements as climate conditions shift is a question that only sustained monitoring can answer.

Subject of Research: First comprehensive mosquito inventory of the Grande Cariçaie wetland at Lake Neuchâtel, Switzerland

Article Title: Inventory of Culicidae in and around the Grande Cariçaie Nature Reserves at Lake Neuchâtel, Western Switzerland

Article References: Flämig, S., Gander, A., & Flacio, E. (2025). Inventory of Culicidae in and around the Grande Cariçaie Nature Reserves at Lake Neuchâtel, Western Switzerland. Alpine Entomology, 9, 103-111. https://doi.org/10.3897/alpento.9.165260

Image Credits: AI Generated

DOI: 10.3897/alpento.9.165260

Keywords: Inventory, Culicidae, around, Grande, Cari, Nature, Reserves, Lake, Neuch, Western, Switzerland, scientific research