Mosquito bacterial communities show stage-specific patterns relevant for vector ecology and AMR surveillance

Mosquito-associated microbiota are influenced by a number of factors, e.g., geography, host species, and developmental stage. Understanding these microbiotas is crucial for assessing their role as vectors and in pathogen dissemination and most studies have largely focused on a few model species, while others like Aedes japonicus remain poorly characterized. Here, we compared the bacterial communities of Aedes albopictus and Aedes japonicus across eight countries: six in Europe, plus the USA and Japan, from both adults and larval stages when possible, using 16S rRNA amplicon sequencing. We found large differences in microbiota composition between mosquito species, with Ae. albopictus exhibiting lower bacterial diversity than Ae. japonicus . Geographic variation in bacterial diversity was also evident, with mosquitoes from Japan and the Netherlands harbouring the most diverse bacterial communities, while Austrian populations displayed the lowest diversity. Developmental stage (adults and larvae) had the strongest influence on bacterial composition, with aquatic-associated genera such as Limnohabitans and Aeromonas dominating larvae, whereas adult mosquitoes harboured higher abundances of Acinetobacter and Methylobacterium . No association was found between Aedes species genetic distance, determined by relatedness, and the bacterial community compositions. A number of bacterial genera with known pathogenic potential, including Pseudomonas , Serratia , Klebsiella , and Acinetobacter , were detected across multiple locations, suggesting that mosquitoes could serve as environmental reservoirs for opportunistic and antimicrobial-resistant bacteria. We identified Wolbachia in Ae. albopictus from Spain and Italy and at low abundances in Ae. japonicus from the USA and Japan, marking one of the first reports of Wolbachia in this species. This is, to our knowledge, the most comprehensive study on Ae. japonicus microbiotas. Our findings provide insights into the ecological and epidemiological implications of mosquito microbiota and emphasize the need for further investigation into their role in pathogen transmission and antimicrobial resistance dissemination.