Abstract While many bee species are experiencing population declines, some host plant generalist bees remain common in Europe, partly because they seem able to shift to new resources. However, foraging on a new alternative plant, such as an invasive species, can modify diet quality and have a potentially detrimental effect on bee health. Herein, we investigated whether the spread of the invasive plant Impatiens glandulifera affects Bombus pascuorum population regarding parasite prevalence, genetic structure, and nest density in Belgium. While no difference in bumble bee genetic structure was detected between invaded and uninvaded sites, we show that I. glandulifera occurrence was significantly correlated with a decrease in the prevalence of Apicystis bombi but not the prevalence of three other parasite species (i.e., Crithidia bombi, Nosema bombi, Nosema ceranae, and Nosema sp.). Regarding our investigations, this effect was likely not due to variation in local bumble bee population fitness before I. glandulifera flowering, nor to the relative abundance of other pollinators such as Apis mellifera, but the unique chemical composition (i.e., polyphenol rich) of the pollen of I. glandulifera remained as an interesting hypothesis. Whereas B. pascuorum queens probably colonize all the potential nesting sites in an area, invaded by I. glandulifera or not, the abundance of polyphenol ampelopsin in pollen from I. glandulifera pollen might reduce local parasite prevalence. Our field study confirms that bumble bee parasite prevalence is potentially related to the particular chemical composition of collected pollen. Plant traits such as secondary metabolite occurrence could play a key role in the health and conservation of bumble bees.
