Five of the nine parasites we screened for were present in 13–53% (depending on the parasite) of the commercially produced bumblebee colonies, with a further three parasites being present in the pollen supplied with the colonies as food (Fig. 1; Tables S2 and S3, Supporting Information). In only 11 of the 48 colonies were the bees screened negative for all of the parasites. Of the 25 pollen samples, only a single sample was free of every parasite. Prevalence of the three bumblebee parasites ranged from 15 to 56% of colonies or pollen samples (Fig. 1). The commercial bumblebees had a somewhat lower prevalence of the honeybee parasites than of the bumblebee parasites, but the Ascosphaera fungal parasite was present in 60% of the pollen samples and only M. plutonius was completely absent from the samples examined. When examined by microscopy, we did not observe Crithidia in the hind guts of the bumblebees, but both Nosema and Apicystis spores were visible. The richness of parasite communities found in the bumblebees did not differ significantly between the two bumblebee subspecies supplied, the three producers or years (χ2 = 0·232, d.f. = 1, P = 0·63; χ2 = 5·04, d.f. = 2, P = 0·081; andχ2 = 0·042, d.f. = 1, P = 0·838, respectively), and there was also no difference between the producers or years in the richness of parasites in their pollen (χ2 = 5·04, d.f. = 2, P = 0·081 and χ2 = 0·581, d.f. = 1, P = 0·446, respectively). However, DWV was more common in bumblebee colonies from 2011 compared with 2012 (7/30 vs. 0/18 colonies; P = 0·036), while the reverse was true for C. bombi (9/30 vs. 11/18 colonies; χ2 = 4·32, d.f. = 1, P = 0·038). N. bombi was found in bumblebees from 5/5 colonies from Producer C, compared with 5/22 from Producer A and 3/13 from Producer B (P = 0·002), while N. apis was found only in pollen samples from Producer B (4/10 samples vs. 0/15 from the other two suppliers; P = 0·048). There were no other significant differences between bumblebee subspecies, producers or years in the number of colonies or pollen samples that carried the different parasites (P > 0·05 in all other cases; Table S6, Table S7, Supporting Information).