Section of the phylogenetic tree of the Bombus terrestris, Apis mellifera, and Drosophila melanogaster gustatory receptors (GRs) showing the impressive B. terrestris-specific expansion. This is a corrected distance tree. B. terrestris and A. mellifera proteins are highlighted in orange and blue, respectively, as are the branches leading to them to emphasize gene lineages. Bootstrap support level in percentage of 10,000 replications of uncorrected distance analysis is shown above major branches. The full phylogenetic tree of GRs can be found in Additional file 1.