Cold and lonely: low-abundance microbiota and no core microbiome across a broad geographic sampling of a mosquito species in Greenland

Microbes are key players in insect ecology and evolution, but host-microbe interactions vary widely in stability and predictability across and within host species. The microbiota of insect clades such as high-latitude mosquitoes remain understudied, despite their high abundance and potential economic and medical relevance. Here, we implemented a novel approach combining amplicon-based species identification, microbial quantification and community composition reconstruction, and joint species distribution modelling, to resolve temporal and spatial variation in the abundance and diversity of bacteria and fungi associated with Ochlerotatus (formerly Aedes) mosquitoes across Greenland. COI amplicon data for 573 mosquitoes collected from five regions of Greenland over 15 years enabled the identification of two species, O. nigripes and O. impiger, revealing an overlap in their distributions and limited within-species genetic structure. Quantitative 16S-V4 rRNA amplicon sequencing showed low bacterial densities compared to other insect species, alongside highly variable microbiota composed of environmentally versatile genera, including Janthinobacterium, Pseudomonas, Serratia, and Escherichia-Shigella. Interestingly, several mosquitoes yielded DNA reads of local vertebrates (likely from blood meals), along with putative vertebrate pathogens such as Bartonella. Fungal communities were low in density and variable in composition, with much of the diversity comprising putative phytopathogens. In contrast, Cladosporium was consistently detected across mosquitoes and controls, indicating likely contamination. Notably, bacterial and fungal communities showed pronounced variation across geographic locations and sampling years, but not between sexes. Together, these findings suggest that Greenland Ochlerotatus mosquitoes do not rely on core microbiota, but engage in flexible associations with diverse, low-abundance microbial communities. They also point to mosquitoes as likely vectors of bacterial and fungal pathogens in the Arctic.