Next Generation Bees: Determining the Floral Resources that Support Wild Bee Reproduction and Pollination Services in Urban Agriculture

Final report for GNC16-233

Project Type: Graduate Student
Funds awarded in 2016: $11,930.00
Projected End Date: 03/31/2020
Grant Recipient: The Ohio State University
Region: North Central
State: Ohio
Faculty Advisor:
Mary Gardiner
The Ohio State University
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Project Information


Since the 1890s, Americans have responded to economic declines by transforming urban vacant land for agricultural production. Similar trends continue today and urban agriculture is revitalizing post-industrial cities, like Cleveland, OH where economic recession has resulted in the formation of over 22,000 vacant lots. Currently, Cleveland hosts an estimated 235 urban farms and this proliferation reflects worldwide interest in urban agriculture initiatives. However, as our world’s 800 million urban farmers try to address food insecurity and support growing human populations, they are faced with land use legacies including soil compaction, contamination, and high degrees of impervious surface—factors which challenge urban pollinators and influence availability of floral and nesting resources. Since research shows that urban bees are critical to urban crop quality and quantity, the sustainability of urban agriculture relies on urban pollinator populations. Therefore, we propose to identify the flowering plants that sustain wild bee populations critical for urban farm pollination in Cleveland, OH.  Our project aims to utilize next generation sequencing tools to: 1) determine the crop and non-crop floral resources found within an urban farm that are important for bee larvae and 2) evaluate if the establishment of “pocket prairies”, or vacant lots seeded with native prairie vegetation, alter bee foraging and improve reproductive success. Through these two objectives, we will identify which cavity nesting bees pollinate urban crops, assess the potential contributions of these solitary bees to urban farm pollination, and make recommendations for on-farm flower plantings that will encourage bees to nest and reproduce near urban farms. In the short term, our project will contribute to important research on how to analyze pollen more effectively and conserve urban pollinators. Long term, our project will inform urban farmers about pollinator resources (both nesting and foraging) and encourage them to improve farming practices to benefit pollinator communities and the services they provide. As economic success is integrally tied to ecological success, our work will support healthier urban environments and more productive urban agriculture.

Project Objectives:

Our research’s long-term goals are to demonstrate the value of cavity nesting bees for urban crop pollination, and examine how to manage urban habitats to support productive bee communities. We will progress towards these general long term goals through two learning outcomes and one action outcome. By the end of our project, we will help 60-100 urban farmers and gardeners learn (1) what crop and non-crop floral resources bees are using on urban farms and (2) if planting prairie plants near nesting sites improves bee reproductive success. Likewise, we will encourage these urban farmers to take action and modify their farm management practices to incorporate pollinator habitat on their farms (Action Outcome).

In order to achieve our learning and action outcomes we will conduct pollinator workshops, field days in urban farms and pocket prairies, extension factsheets, scientific publications, and partner with a farming advisory committee of six Cleveland urban farmers, who will be compensated for their time and participation. Educating our advisory committee and other urban farmers about pollinator communities within urban agroecosystems will provide these growers with the information they need to make sustainable decisions.


Click linked name(s) to expand/collapse or show everyone's info
  • Mary M. Gardiner
  • Reed Johnson


Materials and methods:

Field Work:

  1. We established trap nests at nine urban farms and ten pocket prairies in Cleveland, OH on April 5, 2017.
  2. Trap nests consisted of a PVC pipe filled with thirty cardboard nesting straws (15 cm long) at three diameters (4,6,8 mm) and provided supplementary bee nesting cavities.
  3. Throughout the 2017 and 2018 summers (April-July), we visited each nest biweekly, removed all occupied straws, and replaced them with new straws.
  4. We also completed a floral inventory and measured bloom abundance and area along four 10 m transects, arraying out from each nest in cardinal directions. 
  5. Removed straws were then X-rayed to confirm nesting, and the pollen was dissected from the straws for further molecular analysis.



Pollen Molecular Work:

  1. Pollen samples were homogenized and then lysed with a bead beater machine. We extracted DNA from all of our pollen samples using a phenol chloroform method.
  2. We then used a multi-locus, consensus based approach to pollen metabarcoding-- this means we amplified our pollen DNA at three molecular markers (ITS2, trnl, rbcl) and can estimate a plant species' relative quantity within a pollen ball by calculating the median proportion of sequencing reads across all markers. Only species identified by 2/3 markers will be considered true positives.
  3. For each sample, we conducted 9 PCR reactions (we use a three step process for each molecular marker-- See Richardson et al. 2015 for details) in order to prepare our DNA libraries for sequencing. 
    • Richardson, R. T., C. Lin, J. O. Quijia, N. S. Riusech, K. Goodell, and R. M. Johnson. 2015. Rank-based characterization of pollen assemblages collected by honey bees using a multi-locus metabarcoding approach. Appl. Plant Sci. 3: 1500043.

  4. Next generation Illumina sequencing took place in March 2020 through Ohio State University's Molecular and Cellular Imaging Center (MCIC).
  5. A UTAX algorithm compared sequencing reads to known sequences in the NCBI database and identified plant species. Only species identified by 2/3 markers were considered true positives.


Analysis and Future Work:

We report preliminary, qualitative results below, including a comparison of pollen choices in prairie and farm habitats with a non-metric multidimensional scaled analysis (NMDS). This analysis evaluates if the urban bees foraged on different plant communities when nesting in these unique habitats and at different time points during the sampling season. Likewise, we also report a list of urban crops which were foraged on by bees throughout our project.

In the future, we plan to complete linear regression models to determine what local habitat and landscape factors influence bee's foraging breadth and the proportion of crop pollen visited. 

DNA from collected larvae was sent to the Canadian Centre of DNA Barcoding (CCDB) for further species identifications and we are awaiting results from this analysis.

Research results and discussion:


  • We collected 111 bee nests from 6 urban farms and 8 urban prairies in Cleveland, OH. 
  • All bee nests were X-rayed and then pollen/bees were dissected
  • A total of 559 larvae were counted from our collected nests.
  • DNA extraction is underway.


  • Bee nesting abundances were pretty poor in 2018, but we still collected an additional 36 nests containing 180 bee larvae.
    • (That's a 68% decrease in nest abundances although there were still 5 bees per nest, on average.)
  • We pooled pollen from each nest and have completed DNA extraction for all of our 2017-18 samples.
  • We are 2/3 of the way through our sequencing preparation and are hoping to send our samples out this Spring!



  • After some trouble shooting, we completed our pollen DNA sequencing!
  • We detected 130 plant genera foraged on by bees, although only 30 genera were present in amounts >0.25% of all collected pollen.
  • Our top 10 foraged on plants were as follows:


    Common Name

    Amount %


    Trifolium spp.


    51.3% 100.0%

    Lotus spp.

    Birds foot trefoil

    11.0% 93.2%

    Securigera spp.

    Crown vetch

    11.0% 93.2%

    Cichorium spp.


    3.3% 63.2%

    Vicia spp.

    Hairy vetch

    3.1% 41.4%

    Taraxacum spp.


    2.5% 49.6%

    Rubus spp.


    1.5% 19.5%

    Malva spp.


    1.2% 50.4%

    Potentilla spp.


    1.0% 34.6%

    Zinnia spp.


    0.9% 3.0%

NMDS Ordination Plot of Pollen Communities

  • Our comparison of bee foraging on urban farms and prairies to-date showed no significant difference in the plant community visited by nesting bees (p>0.05)
  • This means that urban cavity nesting bees visit similar plants within the urban landscape, regardless of whether the bees are nesting at a farm or prairie habitat. 
  • In general, exotic Fabaceae weeds dominated each pollen sample and the top 3 species were consistent and independent of nesting habitat location.





Pollen Collected From Urban Farms

  • Crop pollen only accounted for an estimated ~2% of all bee collected pollen
  • We identified at least 27 species which were likely foraged upon from nearby gardens. Species inferences were based off of ITS2 sequence alignments of 98 percent identity or higher.


Common Name

Amelanchier canadensis


Allium cepa


Asparagus officinalis


Anethum graveolens


Borago officinalis


Brassica napus, oleracea and rapa

Cruciferous vegetables

Coriandrum sativum

Coriander and cilantro

Cucumis melo


Daucus carota


Fagopyrum esculentum


Foeniculum vulgare


Assorted Fragaria species


Glycine max


Helianthus annuus


Malus domestica


Mentha spicata


Origanum majorana, vulgare

Marjoram and oregano

Petroselinum crispum


Phaseolus vulgaris

Common bean

Physalis philadelphica


Rheum rhabarbarum


Assorted Rubus species

Blackberries, raspberries and dewberries

Sambucus canadensis


Solanum aethiopicum

Ethiopian eggplant

Solanum lycopersicum


Spinacia oleracea


Zea mays



Preliminary Conclusions

  • Most of the top foraged on plants were non-native spontaneous vegetation, or common urban weeds, in the Fabaceae family (i.e. legumes). However, we have yet to connect which bee species accounted for particular foraging choices. This indicates that it might be beneficial to allow weeds, especially red clover, to grow on urban farms as these non-native plants support bee reproduction.
  • Raspberries and Zinnias were frequent forage on farms, whereas other planted crops or ornamental flowers were not found in high abundances within our bee nest provisions. This suggests that urban cavity nesting bees are likely providing pollination services to urban raspberry crops and that zinnias and raspberries may be appropriate planting recommendations for future on-farm pollinator plantings.


Participation Summary
5 Farmers participating in research

Educational & Outreach Activities

1 On-farm demonstrations
1 Tours
4 Webinars / talks / presentations
2 Workshop field days

Participation Summary:

50 Farmers participated
20 Ag professionals participated
Education/outreach description:

2017: In conjunction with the Cleveland Botanical Garden's Green Corps and the Ohio Ecological Food and Farming Association, Katie and her mentored undergraduate co-presented to an estimated 100-115 urban residents about their research on urban farms and its potential to influence urban pollinators. 

Rodney and Katie also co-conducted two separate field days with 47 youth who were employed as urban farmers through Green Corps. On these field days they broadly taught youth farmers about insects, and then familiarized them with urban pollinators and their role in pollinating crops. 

Katie also traveled to Uppsala, Sweden and presented her research (to-date) to a collaborator's group at the Swedish University of Agricultural Sciences (SLU).

2018: We continued our collaboration with Cleveland's Green Corps of youth urban farmers this year. We developed and ran a workshop about urban biodiversity on the farm. As part of workshop, we taught this year's cohort of youth farmers about insect taxonomy, convinced them to try both insect catching and pinning, and facilitated a scavenger hunt about common plants and insects that occur on urban farms. Involved in this outreach event were Denisha Parker (another NCR SARE recipient) and our two mentored undergraduates, who helped design our workshop stations.

Both Rodney and Katie presented about their research at the annual Entomological Society of America's meeting in Vancouver, BC, Canada in November 2018. Moreover, Rodney successfully defended his dissertation in December and has now accepted a Post-Doc position at York University in Toronto, Canada!

2019: We collaborated with the Cleveland Museum of Natural History to host "From Blight to Bright: Reimagining vacant land to support people and biodiversity in cities"-- a day-long field tour/workshop discussing vacant lot restoration.

We rented a bus and brought ~50 participants on a tour of a 1) vacant lot, 2) pocket prairie, and 3) urban farm. At each site, we discussed research findings that the Gardiner Laboratory has yielded over the past 5 years and their importance.The tour then concluded at the museum with four seminar presentations about 1) urban conservation, 2) Summer Sprout gardening initiatives, 3) the process of prairie construction, and the 4) value of urban trees.

Due to conference coronavirus cancellations, we have not presented research results in person to-date. However, Katie participated in two virtual conferences this spring, 1) Ohio State's College of Food, Agriculture, and Environmental Studies research conference, and 2) the North Central branch of the Entomological Society annual meeting, where she discussed bee foraging in urban pocket prairies.

2020: In May, Rodney accepted a faculty position at the University of Maryland Center for Environmental Science, where he will continue to apply metagenetic techniques to advance pollinator health research. 


Project Outcomes

1 Grant received that built upon this project
Project outcomes:

Our project will contribute to urban agriculture sustainability by elucidating which floral resources are common food sources for important pollinators. We found that weeds (non-native spontaneous vegetation) provide much of the pollen fed to developing bees and thus farmers should consider a relaxed approach to weed management in order to support bee foraging. Especially since planted crops do not always provide continuous blooms, reduced mowing and weeding may help extend food resources for nesting bees. Economically, reduced management may be beneficial to farmers as workers will have more time for crop cultivation and fewer equipment expenses for mowing or herbiciding. Likewise, with better pollination services, crops are expected to increase in quality and quantity-- hopefully benefiting farms financially.

Knowledge Gained:

We assessed partnering farmer's attitude towards and awareness of urban bee conservation through a Project Assessment survey.


In this survey, we asked farmers to describe their motivation to work in urban agriculture, their interest in on-farm pollinator conservation, and barriers to implementing pollinator conservation practices. 

Results from this survey indicated that growers were:

  • Motivated to urban farm for various reasons including job training, income, interest in sustainability and food security
  • Somewhat or Strongly motivated to conserve urban pollinators
  • Generally willing to reserve <5% of their land for bees. Although 2 participants listed 10% and 15%
  • Time and city ordinances were the most common barriers to urban bee conservation
Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.