CONCLUSIONS
This study highlights that even though commercially raised bumble bees typically carry several honey bee viruses, the viral composition generally changes towards bumble bee viruses after field exposure, with no or little impact on colony development. Hence, the widely studied and discussed negative impacts of honey bee virus transmissions to wild pollinators might often be negligible for B. terrestris since neither a coherent establishment of such viruses in the colonies during field exposure nor clear consequences on colony development were found. Additionally, our results highlight the importance of landscape structure in shaping viral patterns during field exposure. Notably, habitat heterogeneity and well-connected agricultural patches in areas with little forest cover led to lower viral loads, fewer viruses, and lower appearance of new viruses in bumble bee colonies. We thus highlight the importance of habitat diversity and heterogeneity in agricultural landscapes, as evidenced numerous times before underline the importance of maintaining existing heterogeneous agricultural landscapes and restoring where necessary.