Barcoding pollen carriage in UK bumblebees

Predicting ecological impact of declining bumblebee (Bombus) populations requires better understanding of interactions between pollinator partitioning of floral resources and plant partitioning of pollinator resources. Here, we combine Cytochrome Oxidase 1 (CO1) barcoding for bumblebee identification and rbcL metabarcoding of pollen carried by bees in three species-rich UK pastures. CO1 barcoding assigned 272 bees to eight species, with 33 individuals belonging to the cryptic Bombus lucorum complex (16 B. lucorum and 17 B. cryptarum). Seasonal bias in capture rates varied by species, with B. pratorum found exclusively in June/July and B. pascuorum more abundant in August. Pollen metabarcoding revealed all bees carried several local pollen species. There was little pollen resource partitioning overall, although several subdominant bee species diverged in pollen carriage at some sites. There was nevertheless evidence of mutual avoidance by the cryptic species. Plant exploitation of bee resources varied by site far more than by plant species. No plant was heavily dependent on just one bee species. We infer that in these communities, most plant species are resilient against the local loss of individual bee species. We advocate combined use of pollen and bee barcoding for further study of plant-pollinator interactions at the landscape scale.