Assessing the attractiveness of native wildflower species to bees (Hymenoptera: Anthophila) in the southeastern United States

Pesticide use, disease, climate change, and habitat loss associated with agricultural intensification and urbanization have contributed to the decline of numerous insect groups. Recent government incentives have recognized the importance of supplementary wildflower plantings to support native bee populations, yet little information exists on the attractiveness of recommended plant species to bees. We evaluated the bee attractiveness of 18 native wildflower species belonging to 6 families (Apiaceae, Apocynaceae, Asteraceae, Fabaceae, Lamiaceae, and Verbenaceae) commonly recommended by the U.S. Department of Agriculture – Natural Resource Conservation Service (USDA-NRCS) to land managers in the southeastern United States. To accomplish this, we planted the 18 wildflower species in separate 1 m2 plots arranged in a randomized block design with four replicates in Auburn, Alabama, USA. We conducted floral counts and timed sweep netting events to assess each species’ attractiveness to bees from May-November 2019. We also evaluated the floral preferences of seven bee taxa (Apis mellifera, Halictus poeyi/ligatus, Bombus griseocollis, Bombus impatiens, Lasioglossum spp., Megachile spp., and Xylocopa virginica) to the planted wildflower species. We found that Asclepias tuberosa, Gaillardia pulchella, and Verbena hastata attracted the greatest abundance, richness, and diversity of native bees compared to the other wildflower species. While several wildflower species attracted low abundance, richness, and diversity of native bees, they are still ecologically important for attracting uncommon or specialist bee species. Each bee taxa were attracted to a particular combination of planted wildflower species; collectively, Asclepias tuberosa, Gaillardia pulchella, and Verbena hastata attracted 89% of all be taxa in the study, which exemplifies the importance of including them in a wildflower mixture to attract native bees. Our results highlight that each species of native wildflower varies in the abundance, richness, and diversity of native bees they attract; this could be considered in the decision-making of landowners and land managers to promote wildflower plantings to reflect their needs.