Data from: Species richness of wild bees, but not the use of managed honey bees, increases fruit set of a pollinator-dependent crop

1. Native, wild bees are important pollinators for both crop and wild
plants. With concerns over the availability and cost of managed honey
bees, attention has turned to native, wild bees as crop pollinators.
However, the ability of native, wild bees to provide sufficient
pollination may depend on their populations at local scales. 2. Therefore,
at the farm scale, we examined the pollination contribution of both
native, wild bees and managed honey bees to apples, and assessed the
relative importance of bee abundance versus species richness. Over three
growing seasons, apple fruit set, bee abundance, and bee species richness
were measured at orchards in Wisconsin, half of which used managed honey
bees, thus allowing us to independently examine the contribution of
native, wild bees to fruit set. We additionally conducted observations of
honey bees and wild bees foraging on apple blossoms in order to examine
functional complementarity. 3. We found that apples are highly dependent
on animal pollinators. However, fruit set was not significantly higher at
orchards with managed honey bees, nor did it increase with the number of
honey bees per orchard. Instead, fruit set significantly increased with
the species richness of native, wild bees during bloom. 4. Honey bees and
wild bees showed different foraging preferences: honey bees more
frequently visited apple flowers on densely blooming trees, while wild
bees showed no preference for floral density, thereby evenly visiting
trees throughout the orchard. 5. Synthesis and applications. Our results
show that native, wild bees play a significant and unique role in apple
pollination within our region, and cannot therefore be replaced by managed
bees. Moreover, our findings suggest that bee conservation efforts should
focus specifically on maintaining or increasing bee species richness in
order to improve pollination and crop yields.