HONEY BEES, BIODIVERSITY AND CLIMATE CHANGE

Honey bees (Apis mellifera) are vital pollinators for both natural ecosystems and agricultural productivity. However, their populations are threatened by factors such as habitat loss, pathogens, climate change, and the genetic risks associated with selective breeding. This thesis explores the genetic and microbial dimensions of honey bee health and productivity within a closed breeding population selected since 2015 for docility, hygienic behavior, and honey production, as part of the Beenomix project in northern Italy. The first study investigates the allelic diversity of the complementary sex determiner (csd) gene, crucial for sex determination in honey bees. Using whole genome sequencing of 100 colonies, 47 distinct csd alleles were identified, including three novel variants, demonstrating that high genetic diversity can be preserved even under selective breeding. These findings underscore the need to include csd diversity as a criterion in breeding programs to prevent the production of sterile diploid males and support colony viability. The second study examines the seasonal dynamics of the gut microbiota and its relationship with key traits such as docility and honey production. Despite seasonal shifts in bacterial abundance driven by dietary changes, a stable core microbiome was consistently observed. Notably, colonies with higher microbial α-diversity, particularly during early summer, were associated with increased honey yield, highlighting a potential link between microbial richness and colony performance. The third study explores the influence of host genetics on gut microbiota composition. Although time of sampling was the predominant factor shaping microbiota structure (β-diversity), differences in microbial richness (α-diversity) among genetic lines were significant. One particular line exhibited both lower microbial diversity and reduced honey production, suggesting a genetic component influencing both microbiota and economically important traits. Together, these studies illustrate the interdependence of genetic and microbial diversity in shaping honey bee health and performance. By integrating csd gene analysis, microbiota profiling, and phenotypic data, this research provides novel insights for developing sustainable and resilient breeding strategies in apiculture. Maintaining biodiversity at both genetic and microbial levels is crucial not only for honey bee survival, but also for securing ecosystem services and agricultural productivity in the context of global environmental change.