ABSTRACT
Urbanization and the expansion of human activities foster radical
ecosystem changes with cascading effects also involving host-pathogen
interactions. Urban pollinator insects face several stressors related to
landscape and local scale features such as green habitat loss,
fragmentation, and availability reduction of floral resources with
unpredictable effects on parasite transmission. Furthermore, beekeeping
may contribute to the spread of parasites to wild pollinators by
increasing the number of parasite hosts. Here we used DNA-based
diagnostics tools to evaluate how the occurrence of parasites, namely
microsporidians (Nosema spp.), trypanosomatids (Crithidiaspp.) and neogregarines (Apicystis bombi ), is shaped by the
above-mentioned stressors in two bumblebee species (i.e, Bombus
terrestris and B. pascuorum ). Infection rates of the two species
were different and generally higher in B. terrestris . Moreover,
they showed different responses towards the same ecological variables,
possibly due to differences in body size and foraging habits supposed to
affect their susceptibility to parasite infection. The probability of
infection was found to be reduced in B. pascuorum by green
habitat fragmentation, while increased along with floral resource
availability. Unexpectedly, B. terrestris had a lower parasite
richness nearby apiaries probably because parasites are prone to be
transmitted among the most abundant species. Our finding supports the
need to design proper conservation measures based on species-specific
knowledge, as suggested by the variation in the parasite occurrence of
the two species. Moreover, conservation policies aiming at safeguarding
pollinators through flower planting should consider the indirect effects
of these measures for parasite transmission together with pollinator
biodiversity issues.