Urban habitat fragmentation and floral resources shape the occurrence of
gut parasites in two bumblebee species
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 (Crithidia spp.) 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.