Honey bees and wild pollinators differ in their preference for and use of introduced floral resources

Introduced plants may be important foraging resources for honey bees and
wild pollinators, but how often and why pollinators visit introduced
plants across an entire plant community is not well understood.
Understanding the importance of introduced plants for pollinators could
help guide management of these plants and conservation of pollinator
habitat. We assessed how floral abundance and pollinator preference
influence pollinator visitation rate and diversity on 30 introduced vs. 24
native plants in central New York. Honey bees visited introduced and
native plants at similar rates regardless of floral abundance. In
contrast, as floral abundance increased, wild pollinator visitation rate
decreased more strongly for introduced plants than native plants.
Introduced plants as a group and native plants as group did not differ in
bee diversity or preference, but honey bees and wild pollinators preferred
different plant species. As a case study, we then focused on knapweed
(Centaurea spp.), an introduced plant that was the most preferred plant by
honey bees, and that beekeepers value as a late-summer foraging resource.
We compared the extent to which honey bees vs. wild pollinators visited
knapweed relative to co-flowering plants, and we quantified knapweed
pollen and nectar collection by honey bees across 22 New York apiaries.
Honey bees visited knapweed more frequently than co-flowering plants and
at a similar rate as all wild pollinators combined. All apiaries contained
knapweed pollen in nectar, 86% of apiaries contained knapweed pollen in
bee bread, and knapweed was sometimes a main pollen or nectar source for
honey bees in late summer. Our results suggest that because of diverging
responses to floral abundance and preferences for different plants, honey
bees and wild pollinators differ in their use of introduced plants.
Depending on the plant and its abundance, removing an introduced plant may
impact honey bees more than wild pollinators.