The microbes living inside a mosquito may be tiny, but their influence on disease transmission is anything but small. The bacterial communities that colonize a mosquito’s gut and tissues can shape the insect’s physiology, its immune responses, and even its ability to acquire and transmit pathogens such as malaria parasites and arboviruses. Yet despite decades of research, scientists have struggled to map which factors actually determine the composition of these microbial communities in wild mosquito populations, rather than in the laboratory. A new study published in Microbial Ecology offers one of the most detailed field-based portraits to date, revealing how mosquito species, geography, season, and infection with avian malaria parasites each leave a measurable imprint on the mosquito microbiome.

An international research team led by Marta Garrigós of the Estación Biológica de Doñana (EBD-CSIC) in Seville, Spain, together with colleagues from institutions across Andalusia, set out to disentangle these drivers using an ambitious sampling program in southern Spain. Between spring and autumn of 2022, the researchers collected mosquitoes from five localities, targeting three common and ecologically distinct species: Culex pipiens, Aedes albopictus, and Culiseta longiareolata. Each of these species occupies a different niche in the human landscape. Culex pipiens, the northern house mosquito, thrives in urban and peri-urban environments and is a key vector of West Nile virus and avian malaria parasites in Europe. Aedes albopictus, the Asian tiger mosquito, is an invasive species that has spread rapidly across the continent and is capable of transmitting dengue, chikungunya, and Zika viruses. Culiseta longiareolata, by contrast, is a less medically prominent species that frequently breeds in artificial and natural containers, including water tanks and stone basins.

The team analyzed a total of 196 mosquito pools, each containing four female mosquitoes, using 16S rRNA metabarcoding. This technique amplifies and sequences a variable region of the bacterial 16S ribosomal RNA gene, allowing researchers to identify the bacterial taxa present in each sample without the need to culture the organisms, which is notoriously difficult for the majority of environmental bacteria. By processing pooled samples, the study could capture the collective bacterial community carried by small groups of wild-caught females, balancing sequencing depth with broad ecological coverage.

The results revealed striking differences among the three mosquito species. Alpha diversity, a measure of the number and evenness of bacterial types within a sample, was significantly higher in Culiseta longiareolata than in either Culex pipiens or Aedes albopictus. Meanwhile, beta diversity, which quantifies differences in community composition between samples, also varied strongly by host species. In other words, the three mosquito species each harbored distinct bacterial neighborhoods, suggesting that host identity is a powerful filter shaping which microbes can establish themselves in the mosquito body.

Perhaps the most dramatic finding concerned the endosymbiotic bacterium Wolbachia. This maternally inherited microbe is famous among biologists for its ability to manipulate the reproduction of its insect hosts, and it has become a major tool in the fight against mosquito-borne diseases: releases of Wolbachia-carrying Aedes mosquitoes have been shown to suppress virus transmission in several countries. In the southern Spanish samples, Wolbachia dominated the bacterial communities of both Culex pipiens and Aedes albopictus, but was virtually absent from Culiseta longiareolata. This pattern suggests that Wolbachia can reach near-fixation within wild populations of two major vector species while leaving related species untouched, with potentially profound consequences for how these insects interact with viruses and parasites.

To probe the environmental dimension of microbiome variation, the researchers focused on Culex pipiens, the most extensively sampled species in the study, and examined how sampling locality, season, and infection status with avian Plasmodium parasites, the agents of avian malaria, shaped its bacterial community. Both locality and season influenced alpha and beta diversity. Mosquitoes collected in autumn from the coastal locality of Fuengirola showed the highest observed richness, indicating that even within a single species, the bacterial load and variety can fluctuate dramatically depending on where and when the insects are caught.

The study also revealed a technical subtlety that is increasingly recognized in microbial ecology: differences in beta diversity among localities and seasons could be influenced, at least in part, by differences in beta dispersion. In essence, some groups of samples showed more variability in their community composition than others, and this heterogeneity in spread can mimic or obscure genuine differences in average community composition. By accounting for dispersion, the researchers were able to interpret their results more rigorously, distinguishing between cases where communities differ in their central composition and cases where one group is simply more variable than another.

Infection status added another layer of complexity. The relative abundance of different bacterial taxa in Culex pipiens varied according to whether the mosquitoes were infected with avian Plasmodium parasites. This observation aligns with a growing body of evidence that vector-borne pathogens do not interact with their mosquito hosts in a microbial vacuum. Malaria parasites must navigate a series of barriers within the mosquito, including the midgut epithelium, and the resident microbiota can interfere with or facilitate these journeys. Some gut bacteria are known to prime the mosquito immune system or produce molecules that directly inhibit Plasmodium development, while others may create conditions more favorable to parasite survival. The correlation reported here cannot establish causation, since it is possible that infection alters the microbiome, the microbiome alters susceptibility to infection, or environmental factors shape both simultaneously. Still, the finding reinforces the idea that the tripartite interaction among mosquito, microbiome, and pathogen is a critical axis of transmission ecology.

The implications of this work extend beyond basic science. Strategies to control mosquito-borne diseases increasingly rely on manipulating the microbiome, whether through Wolbachia-based population replacement, the use of probiotic bacteria to reduce parasite development, or environmental management that alters the microbial landscapes mosquitoes encounter. Designing such interventions rationally requires knowing which factors govern microbiome composition under natural conditions. If locality and season strongly influence the bacterial community, as this study demonstrates, then interventions may need to be tailored to specific regions and timed to particular parts of the transmission season to remain effective. The dominance of Wolbachia in Culex pipiens and Aedes albopictus in southern Spain also provides a baseline against which future microbiome changes, whether driven by climate change, urbanization, or biocontrol releases, can be measured.

The study also highlights the value of sampling wild mosquitoes across multiple dimensions of ecological variation. Many microbiome studies rely on laboratory colonies, which harbor simplified and often unstable bacterial communities, or on single sampling events that cannot capture temporal dynamics. By collecting mosquitoes repeatedly across spring, summer, and autumn, and across five localities spanning urban, semi-natural, and managed environments, including a collaboration with the Bioparc Fuengirola, the team built a framework that captures the real-world variability that any control program would face.

The research, which was supported by grants from the Spanish Ministry of Science, Innovation and Universities and co-financed by European Union funds, and carried out within the CIBER Epidemiología y Salud Pública network, represents a collaborative effort spanning parasitology, genomics, and animal ecology. Open-access publication was enabled through the CRUE-CSIC agreement with Springer Nature, ensuring that the dataset and findings are freely available to researchers, public health officials, and vector control programs across Europe and beyond.

As mosquito-borne pathogens expand their ranges in a warming and urbanizing world, understanding the invisible communities inside the insects that carry them may prove as important as studying the pathogens themselves. This study provides a comprehensive framework for understanding the ecological drivers of the wild mosquito microbiome, a key step toward predicting vector-pathogen interactions and improving strategies for vector-borne disease control. What remains to be determined is whether the microbial differences documented here translate into meaningful variation in vectorial capacity in nature, a question the authors argue should be addressed in future work.

Subject of Research: Drivers of microbiome composition in wild mosquito populations, examining the effects of mosquito species, sampling locality, season, and avian Plasmodium infection in southern Spain.

Subject of Research: Biology

Article Title: Drivers of Mosquito Microbiome Composition: Effects of Species, Locality, Season, and Plasmodium Infection

Article References: Garrigós, M., Veiga, J., Garrido, M., García-López, M. J., Morales-Yuste, M., Marín, C., Recuero, J., Rosales, M. J., Moreno-Indias, I., & Martínez-de la Puente, J. (2026). Drivers of Mosquito Microbiome Composition: Effects of Species, Locality, Season, and Plasmodium Infection. Microbial Ecology. https://doi.org/10.1007/s00248-026-02801-7

Image Credits: AI Generated

DOI: 10.1007/s00248-026-02801-7

Keywords: mosquito microbiome, Aedes albopictus, Culex pipiens, Wolbachia, avian malaria, Plasmodium, 16S rRNA metabarcoding, vector-borne disease, Culiseta longiareolata, microbiota, environmental variation, invasive species

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Morgan Morrow. (September 8, 2026). Drivers of Mosquito Microbiome Composition: Effects of Species, Locality, Season, and Plasmodium Infection. Scienmag. https://scienmag.com/drivers-of-mosquito-microbiome-composition-effects-of-species-locality-season-and-plasmodium-infection/

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