Date of Award
Master of Science
Ecology, Evolution, and Organismal Biology
Ecology and Evolutionary Biology
Mary A. Harris
John D. Nason
Landscapes dominated by agriculture offer little vegetative heterogeneity and are frequently disturbed by farming practices. In Iowa, 72% of the land is devoted to the production of corn (Zea mays L.) and soybean (Glycine max L.), neither of which require animal-mediated pollination, thus provide few resources for pollinators. An approach to mitigating the negative impacts of highly intensive agricultural practices on the surrounding landscape is the implementation of Conservation Reserve Program (CRP) contour buffer and filter strips within agricultural fields. This study assessed the impact of such strips with varying plant diversities on the local native bee communities. Surveys of bee communities were conducted at eleven sites throughout Iowa using traps (bowl, blue vane, and emergence) and netting techniques. Vegetation surveys were also conducted to determine blooming floral diversity within the strips at each site. After five years of surveys, we found statistically significant relationships between native bee abundance and floral coverage within the strips as well as between bee species richness and floral species richness. Additionally, in the third year of the study, we established experimental plots of bare ground within flight distance of the strips to serve as potential nesting habitat for ground-nesting bees. In subsequent evaluations of these plots, we collected 330 individual bees representing 30 species. Based on these results, it is clear that contour buffer and filter strips with greater blooming floral diversity have the potential to offer quality forage and establishing bare soil plots increases nesting resource availability, ultimately supporting bee communities of greater diversity than areas lacking these essential habitat components. Furthermore, we wanted to address the floral species included in seed mixes intended to support bees. Using a targeted-sweeping method, in which a bee was collected from a known flower and stored individually, we collected 610 bees representing 58 species and identified the pollen carried by each bee. A total of 63 pollen species were identified despite bees being collected from only 31 floral species. From these data, we were able to create networks relating bee species and the floral species from which each bee was collected as well as the bee species and the carried pollen species. The interactions between bees, pollen, and flowers revealed that the following floral species were utilized by the greatest number of bees and bee species: Asclepias syriaca L., Erigeron annuus L., Heliopsis helianthoides L., Monarda fistulosa L., Ratibida pinnata Ventenat, Rudbeckia hirta L., Silphium perfoliatum L., Solidago canadensis L., and Zizia aurea L. The methodology employed in this study can be applied to additional ecotypes and regions to determine which floral species support the most diverse bee community and should be included in seed mixes designed to do so. In these studies, we have provided several strategies to provide or improve habitat for native bees within agricultural systems. Establishing contour buffer and filter strips, providing bare soil areas for ground-nesting bees, and including appropriate floral species in seed mixes are methods that can be used to lessen the effects of agricultural practices on the landscape while simultaneously increasing biodiversity in a heavily altered region.
Mackert, Morgan, "Strategies to improve native bee (Hymenoptera: Apoidea) habitat in agroecosystems" (2019). Graduate Theses and Dissertations. 17255.
Available for download on Friday, April 24, 2020