Honeybee visitation to shared flowers increases Vairimorpha ceranae
prevalence in bumblebees
Abstract
Vairimorpha (=Nosema) ceranae is a widespread pollinator parasite that
commonly infects honeybees and wild pollinators, including bumblebees.
Honeybees are highly competent V. ceranae hosts and previous work in
experimental flight cages suggests V. ceranae can be transmitted during
visitation to shared flowers. However, the relationship between floral
visitation in the natural environment and the prevalence of V. ceranae
among multiple bee species has not been explored. Here, we analyzed the
number and duration of pollinator visits to particular components of
squash flowers—including the petals, stamen, and nectary—at six
farms in southeastern Michigan, USA. We also determined the prevalence
of V. ceranae in honeybees and bumblebees at each site. Our results
showed that more honeybee flower contacts and longer duration of
contacts with pollen and nectar was linked with greater V. ceranae
prevalence in bumblebees. Honeybee visitation patterns appear to have a
disproportionately large impact on V. ceranae prevalence in bumblebees
even though honeybees are not the most frequent flower visitors. Floral
visitation by other pollinators was not linked with V. ceranae
prevalence in bumblebees. Further, V. ceranae prevalence in honeybees
was unaffected by floral visitation behaviors by any pollinator species.
These results suggest that honeybee visitation behaviors on shared
floral resources may be an important contributor to increased V. ceranae
spillover to bumblebees in the field. Understanding how V. ceranae
infection risk is influenced by pollinator behavior in the shared floral
landscape is critical for reducing parasite spillover into declining
native bee populations.