Aim: Many social insects introduced beyond their native ranges have become globally 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 and spread of B. terrestris is intricately connected with its gut microbiome, diet, and the environment. This study investigates how the gut microbiota of B. terrestris workers is affected by nutritional diversity (foraged pollen biome) and environmental variation across diverse landscapes in an invaded island system.

Location: Tasmania, Australia

Method: B. terrestris female workers were sampled from 19 sites across Tasmania, for which environmental data for seven variables were extracted. We obtained gut microbiome data for 16/19 (N = 92 bees) sites using 16s rRNA metabarcoding, and ITS2 metabarcoding from foraged pollen to obtain flowering plant diversity from 17/19 sites.  We examined how pollen diversity, environmental variables and their interactions influence gut bacterial diversity, richness and community composition.

Results: 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 foraged 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 the most strongly weighted variable, which, together with pollen diversity, negatively affected gut bacterial diversity.

Conclusions: Our findings uncover how environmental interactions affect the gut microbiome of B. terrestris in an invaded landscape with novel nutritional resources. This contributes to understanding the factors that predict the spread and persistence of invasive bumblebees globally.

B. terrestris female workers were sampled from 19 sites across Tasmania, for which environmental data for seven variables were extracted. We obtained gut microbiome data for 16/19 (N = 92 bees) sites using 16s rRNA metabarcoding, and ITS2 metabarcoding from foraged pollen to obtain flowering plant diversity from 17/19 sites.  Data were sequenced using Illumina MiSeq 2x150 bp.