Lorenzo Assentato: The influence of host-environment interactions in shaping insect microbiota: limitations and considerations

Abstract

This thesis investigates insect-associated microbiota and the statistical approaches used to study them, with a particular focus on how environmental context shapes microbial community composition. The work encompasses three main research aims. First, we examined the microbiota of Anopheles mosquitoes, assessing how breeding-site characteristics, such as habitat type, and the physicochemical properties of aquatic environments, influence site and larval microbial communities and the link between those. We also explored whether a trace of adult host-seeking behavior, specifically preference for human or cattle hosts, can be recognized in mosquito microbial composition, and how these patterns reflect the surrounding environment.

Second, we investigated microbial communities in Cicadellidae (Membracoidea) and their parasitoid wasps (Hymenoptera and Strepsiptera) to evaluate whether parasitization influences leafhopper symbionts. By sampling host–parasitoid pairs, we identified instances in which microbial strains occurred in both insects, suggesting that transient microbial transfer may occur during parasitization and could, over evolutionary time, contribute to stable symbiotic associations.

Finally, we addressed methodological challenges in microbial ecology by developing a framework for choosing a threshold for rarefation, a widely used normalization procedure for 16S rRNA sequencing data. The resulting tool, Sibyl, provides a data-driven approach for threshold selection and offers users clearer insights into how preprocessing decisions may influence downstream analyses.

Environmental context emerges as a major determinant of insect microbiota, influencing through a complex network of interactions, both the microbial pools available to insects and the communities they ultimately harbor.