Landscape viromics of introduced honeybees and bumblebees reveal distinct environmental and host-specific effects

Understanding how viral communities vary across co-occurring hosts and environments is essential for assessing species-specific viral risks under changing land use and climate. This is particularly relevant for managing introduced bees, which face persistent viral threats themselves, as well as transmitting plant viruses. Here, we compare RNA viromes of the long-established honeybee (Apis mellifera, introduced to Tasmania in 1831) and the more recent invader, the bumblebee (Bombus terrestris, invasive since 1992), across 14 Tasmanian sites - an island still free of the viral vector, Varroa destructor. Using a metatranscriptomic approach on total RNA from whole bees, we identified insect- and plant-associated viruses and inferred phylogenetic patterns of insect viral sharing, divergence, and potential cross-species transmission. We also assessed spatial and environmental drivers of viral composition, diversity, and richness. Geographic longitude, precipitation, temperature, and pasture percentage influenced the total, insect-, and plant-associated viromes of B. terrestris. In contrast, for A. mellifera, only precipitation and temperature were associated with insect and plant viral alpha diversity and community composition. Phylogenetic analyses revealed that Black Queen Cell virus in A. mellifera from Tasmania has diverged from mainland Australian sequences, and two distinct sub-strains of Lake Sinai virus 1 were shared by both bee species. Lake Sinai virus 3 showed evidence of interspecies transmission between A. mellifera and B. terrestris. Notably, this study provides the first detection of Moku virus in Australian bees and globally in bumblebees, suggesting potential interspecies transmission among social Hymenoptera. Overall, our findings demonstrate local viral diversification and reveal that B. terrestris viromes are more strongly shaped by environmental factors than those of A. mellifera, underscoring the importance of monitoring invasive pollinators as reservoirs and vectors of viral emergence.