Landscape-wide metabarcoding of the invasive bumblebee (Bombus terrestris) shows interactions among the gut microbiome and pollenbiome

Many species of social insects introduced to regions beyond their native ranges have become highly invasive. The introduction of the eusocial European buff-tailed bumblebee, Bombus terrestris , to the island of Tasmania (Australia) ∼30 years ago is of concern due to its ecological impacts and its potential to spill over pathogens to native bees or commercially important honeybees. The health of B. terrestris is intricately connected with its gut microbiome and diet; however, environmental variables may also interact, particularly during invasion into novel environments. Using landscape-wide sampling and a metabarcoding approach to characterize the gut bacteria (16S rRNA) and diet composition from foraged pollen (ITS2: floristic diversity of pollen baskets), this study investigates how the gut microbiota of B. terrestris workers is affected by nutritional diversity (‘pollenbiome’) and environmental variation across diverse landscapes of its invasive range in Tasmania. Gut bacterial community composition and diversity were significantly predicted by site annual precipitation and percentage of pasture. Further, a positive interaction between site annual precipitation and site annual temperature significantly predicted gut bacterial diversity. The interaction effect of pollen diversity and average summer wind velocity was also significantly and positively related to gut bacterial diversity. Following comparison of Akaike information criterion (AIC) and sum of weights, the percentage of pasture was identified as the most strongly weighted variable, which, along with pollen diversity, had a negative impact on gut bacterial diversity. These insights help to uncover how environmental interactions affect the gut microbiome of B. terrestris in an invaded landscape with novel nutritional resources. This knowledge contributes to understanding the factors that predict the spread and persistence of invasive bumblebees.