Microplastic-Induced Dysbiosis in Aedes aegypti and Aedes albopictus Larvae Without Immune Activation

Background: The pollution of microplastics (MP) is fast becoming a growing ecological threat. It holds potential implications for disease-incubation species such as Aedes aegypti, Aedes albopictus. While previous studies have examined the toxic effects of MPs on aquatic invertebrates, little is known about their impacts on the microbiota and immunity of mosquitoes. Objective: This study investigates how the ingestion of larvae changes the bacterial community and exhibiting of immune gene expression in two important species of mosquito having both medical and commercial value. Methods: First-instar Aedes aegypti and Aedes albopictus larvae were exposed to 1 µm polystyrene microbeads containing carboxyl-modifying dyes at environmentally relevant concentrations (0, 1000, 10 000 MP µL −1 ) for the duration of their stage development until pupation. 16S rRNA and ITS2 sequencing was carried out on the Illumina MiSeq platform to assess microbial diversity. qPCR was used to quantify the relative expression levels of Toll and IMD pathway immune genes Defensin A, Cecropin A, Relish and Dorsal, and analyzed with the ∆∆Ct method of calculation. Key discoveries: Exposure to MPs ultimately lead to significant bacterial dysbiosis, characterized by decreasing Shannon diversity and changes in community composition that benefited Pseudomonas and harmed Acinetobacter. The fungal microbiota, however, was largely unaffected by these changes of housekeeping in the bacterial population. Despite these shifts in the microbiome, there was no significant upregulation of immune genes across all treatments. Conclusion: In Aedes larvae, foodborne MP exposure impacts the gut microbiota without inducing significant transcriptional immune responses. Such microbiome changes might subtly influence vector competence or disease resistance in their hosts, thus begging the question of whether water pollution-induced modifications to mosquito ecology should be considered during vector control measures.