Parasite Prevalence May Drive the Biotic Impoverishment of New England (USA) Bumble Bee Communities

SIMPLE SUMMARY: Here we discuss widespread changes in the community structure of bumble bees (Bombus spp.) found in the coastal-zone community of New England. One species in particular, Bombus impatiens Cresson, 1863, has increased in relative abundance nearly 45% since the 1990s to become the dominant species in the region, representing nearly 75% of all Bombus individuals collected in our studies. These changes in abundance may be, in part, due to differences in infection rates by microparasites, with B. impatiens having significantly fewer microparasites than several other less common and declining Bombus species. We discuss the possible role of microparasites in influencing the community composition of Bombus species in our region, and how these infections might be compounding declines in conjunction with habitat loss and climate change. ABSTRACT: Numerous studies have reported a diversity of stressors that may explain continental-scale declines in populations of native pollinators, particularly those in the genus Bombus. However, there has been little focus on the identification of the local-scale dynamics that may structure currently impoverished Bombus communities. For example, the historically diverse coastal-zone communities of New England (USA) now comprise only a few species and are primarily dominated by a single species, B. impatiens. To better understand the local-scale factors that might be influencing this change in community structure, we examined differences in the presence of parasites in different species of Bombus collected in coastal-zone communities. Our results indicate that Bombus species that are in decline in this region were more likely to harbor parasites than are B. impatiens populations, which were more likely to be parasite-free and to harbor fewer intense infections or co-infections. The contrasting parasite burden between co-occurring winners and losers in this community may impact the endgame of asymmetric contests among species competing for dwindling resources. We suggest that under changing climate and landscape conditions, increasing domination of communities by healthy, synanthropic Bombus species (such as B. impatiens) may be another factor hastening the further erosion of bumble bee diversity.