Wildflower plantings on fruit farms provide pollen resources and increase nesting by stem nesting bees

Abstract

AbstractWildflower plantings on farms have been shown to attract foraging wild bees, however, whether these added floral resources increase nesting densities of bees remains largely untested. We placed nest boxes containing natural reeds at 20 fruit farms in Michigan. We then compared nesting densities between farms with and without wildflower plantings and analysed nest provisions to evaluate use of wildflower plantings for brood provisioning. We found significantly greater nesting at farms with wildflower plantings, with only one out of 236 completed nests at a farm without a planting. The majority of nests were completed by Megachile pugnata, with a portion of nests completed by Osmia caerulescens. We found that nesting bees collected pollen from only a subset of the available flowers in the wildflower plantings, with a strong preference for Centaurea maculosa, and Rudbeckia type pollens. While these species were found growing in the plantings, only Rudbeckia type species were seeded in the plantings. This study provides evidence that wildflower plantings (though not only seeded species) are filling a critical resource gap for stem‐nesting bees in agricultural landscapes and likely support local populations.