Bee (Hymenoptera: Apoidea) diversity and floral use in remnant and planted tallgrass prairies of Northeast Iowa

Within tallgrass prairie ecosystems, bees (Hymenoptera: Apoidae) play a significant role in providing the important ecosystem service of pollination.  However, land use changes have severely reduced the availability of floral resources upon which native bees depend.  We investigated bee diversity and abundance within remnant and planted tallgrass prairies in Northeast Iowa.  Bees were collected every 2-3 weeks from four remnant and four planted prairies using a directed search method which involved collecting every bee observed on a flower and recording that species of plant.  Bees were separated into morphospecies for later identification, and species richness and abundance were calculated for each prairie.  858 bees belonging to 128 different morphospecies were collected.  Commonly observed bee species included Bombus griseocollis, Bombus impatiens, Bombus auricomus, Apis mellifera, and Peponapis pruinosa, as well as several species of Halictidae and Andrenidae.  Floral diversity was measured by recording each species of flowering plant observed during each sampling period.  Floral resource availability was estimated by measuring floral surface area in 10 random 0.5m² quadrats using ImageJ.  Bee abundance and species richness was similar in burned (411 bees, 83 species) and unburned prairies (448 bees, 90 species), but surprisingly, both species richness and abundance were lower in remnant (259 bees, 72 species) than planted prairies (571 bees, 95 species).  Bees were collected from 79 species of flowers, but only Amorpha canescens, Baptisia alba, Echinacea pallida, Erigeron strigosus, Erygium yuccifolium, Monarda fistulosa, Veronicastrum virginianum, and Zizia aurea were utilized by more than 10 species of bees.