The role of cover crops as a floral resource for native bee conservation in agroecosystems

2013 Annual Report for GNE12-037

Project Type: Graduate Student
Funds awarded in 2012: $14,929.00
Projected End Date: 12/31/2014
Grant Recipient: Penn State University
Region: Northeast
State: Pennsylvania
Graduate Student:
Faculty Advisor:
Mary Barbercheck
PSU Dept. of Entomology

The role of cover crops as a floral resource for native bee conservation in agroecosystems


     Conservation of natural processes such as pollination, pest control, and nutrient cycling are essential to maintaining a healthy agroecosystem. The incorporation of cover crops into annual crop rotations is one practice that is used in the Northeast U.S. to manage soil fertility, weed suppression, and erosion control. Additionally, cover crops that have a flowering stage have the potential to support beneficial insect communities, such as native bees. Because of the current decline facing managed honeybee colonies, the conservation of native bee communities is critical to maintaining ‘free’ pollination services. However, native bees are negatively affected by agricultural intensification and are in decline across North America. This project assesses the potential of flowering cover crop species to act as a conservation resource for native bee communities, in addition to providing benefits to soil fertility and agricultural production.
     Three flowering cover crop species were studied in this project over four fall planting dates. I evaluated each cover crop and planting date treatment for differences in winter survival, spring blooming time, flower density, and the subsequent influence that each of these factors had on native bee visitation. The three cover crop species bloomed at different times throughout the spring and attracted significantly different native bee communities. Planting date did not majorly influence spring flowering time, but did have a significant influence on winter survival. Across all three cover crop species, the planting date treatments with the lowest winter survival had lowest spring flower density which then resulted in the lowest bee visitation frequency. Overall, the main influences on bee community visitation were cover crop species and total flower density. Additionally, as the variations in winter survival and spring flowering time demonstrated, considering cash crop rotation window timing limitations is important to select appropriate cover crop species so that flowers are produced within the cover crop window timeframe.

Objectives/Performance Targets

OBJECTIVE 1: To identify (a) the blooming time frames of three common Northeast U.S. flowering cover crop plant species, and (b) the effect of cover crop planting and termination date on peak bloom.
Objective 1 accomplishments to date:
     The original proposal was designed to study six cover crop species over two fall planting dates. After contemplation this was altered to three cover crop species and four planting dates so as to better represent a fall planting gradient and allow for a more robust model for how these planting dates would fit into a variety of Northeast cash crop rotations. This also allowed for a greater variety of fall climate effects on each planting date to be observed.
     Data has been collected and analyzed on the overall spring blooming time of each of the three cover crop species studied as well as how this blooming time differed across planting dates. Each crop and planting date was monitored outside of a standard cash crop rotation window and thus the effect of spring termination time is represented by where the date of cover crop termination would fall relative to when each crop and planting date bloomed. Each treatment was monitored for starting and ending date of flower production as well as for relative flower density across time.  


OBJECTIVE 2: To identify (a) the native bee species that visit cover crop flowers for pollen and nectar resources, (b) when those bee species are most abundant in the environment and how that relates to cover crop bloom, and (c) what potential pollinator benefits may be lost through early termination of cover crops in standard crop rotations.
Objective 2 accomplishments to date:
     All bee visitors to the three cover crop species and planting dates were monitored once per week throughout the blooming period of each crop. On each data collection day, pollinators were visually monitored for two minutes per plot, once in the morning and once in the early afternoon. Following each visual observation period, one minute of hand-netting was performed to collect and return the bees observed to the laboratory for identification to species.
     Along with this plot-level bee data, I also set a series of landscape-level bee traps to collect the potential bee community in the local environment. I set out five different traps, replicated each eight times across the site. These five traps consisted of two trap types (pan traps and vane traps) and three different trap colors (blue, yellow and white). The traps were set once per week for 48 hours. The goal of these landscape-level traps was to be able to compare the potential native bee community to the actual sub-set that was utilizing the flowering cover crops; however, the traps did not sample all potential bee species in the area as several species were collected on the cover crops but not in any of the five landscape trap types. For this reason a direct comparison of cover crop bee use versus total bee community potential was not performed.
     Again, as this study was performed outside of a standard cash crop rotation window, the potential pollinator benefits lost in different rotation windows was considered based on the blooming time of each cover crop species in relation to the number of bees served by that crop and a standard cover crop termination date of a specific rotation schedule.


OBJECTIVE 3: (a) To participate in a series of public outreach activities highlighting the benefits of flowering cover crops for conservation of native bee species. (b) To create and distribute an extension publication that illustrates the results of this project and assists growers in determining the optimal species for use in their rotation.
Objective 3 accomplishments to date:
     The data from this study was shared at two summer Penn State Extension field day events. The first took place on September 7, 2013 on the organic grain farm of one of the farmer contributors of a corresponding cover crop research project of which I am a part. The second field day was held on September 11, 2013 and took place on the research farm of Penn State where this project was conducted. For both extension field day events I was able to spend 15-20 minutes educating the participants on the importance of native pollinators, their diversity and natural history, their agriculture conservation needs, and ways in which we can select flowering cover crop species to assist the conservation of these beneficial insects. I also included questions on field day evaluations regarding the participant’s previous knowledge of native pollinators, knowledge gained via my presentation, and future interest in planting flowering cover crops for the use of native pollinator communities.
     Currently I am in the process of producing an informative Penn State Extension document summarizing the results of my study. This document will either be printed for public distribution at future field days or similar events, or else it will be published online on the Penn State Extension and Entomology websites and is set to be finished by early 2014.


     The field work and data collection for 2013 progressed smoothly and essentially as planned. All crops were monitored for growth and signs of spring flower production starting in early May. The canola crops began to flower first during the last week of May and thus the true data collection began at that time as well. In total I conducted eleven weeks of data collection from the end of May into the second week of July.
     The three cover crop species bloomed roughly in sequence with limited overlap between crop blooming periods. During the flowering time of each crop, myself and a single field assistant spent an average of 2-3 days per week in the field collecting bee data from the flowering cover crop plots, monitoring plant growth and flower density over time, and setting landscape-level bee traps. The remaining days were spent in the laboratory sorting through the bee samples collected in the field and entering data onto computer spreadsheets. All data collection was repeated weekly from early-May until early-July.
     Cover crop plots were maintained during this period to limit weed growth in areas where weed competition may have had an influence on cover crop growth, although this control decreased over time as crops grew more robust and field time became more restricted. Additionally, each cover crop species was individually terminated on a plot-by-plot basis after all flowers had senesced and before final seed production. This was done to limit reseeding of the cover crop and to reduce the risk of it becoming a weed for future crops grown in the plot area.
     After mid-July, attention and time management switched from field data collection to data analysis and bee species identification. Bee species IDs were conducted on-site as much as possible using resources available on campus or via the internet, but further assistance was required for several of the more difficult bee genera. In order to finish the task of identifying all the bees to species-level, I contacted a bee taxonomist at Michigan State University and traveled to his laboratory for several days in September to finish the process of identifying all of my collected specimens.
     I also had the opportunity to share the results of my research at two cover crop-focused extension field days, (both in early September) as well as at two scientific conferences (one in mid-August and the second in mid-November). Throughout these exciting and informative experiences I had a series of positive interactions with local organic farmers, other agricultural and pollinator researchers, NRCS employees, and pollinator conservation specialists. Most of these people showed great interest in the topic of my research and felt it had potential for practical application and on-farm adoption.

Impacts and Contributions/Outcomes

     This project has been designed to provide information vital for extension agents or conservation specialists to be able to give informed recommendations on using flowering cover crops as a pollinator conservation strategy. While the idea of using flowering cover crops for pollinator benefit is not necessary new, the information available to the public at this time is mostly anecdotal. Because of this, the information is often deficient in detail on how various agronomic management properties such as fall cover crop planting date and spring termination date affect the blooming resource of various cover crop species. Therefore, the results from this research project, in combination with a consecutive experiment comparing cover crop diversity levels to pollinator floral resource potential, will provide specific data on how some of these farmer management choices or limitations influence the native bee conservation potential of three common, Northeastern U.S. cover crops.
     During this past summer I was fortunate enough to have been able to share the results of my research project with farmers and other sustainable agricultural professionals at two different farmer extension field days. The first event was held on September 7, 2013 in Milton, PA at the home of an organic forage grain farmer and Penn State research collaborator. The topic of this event was ‘Cover Crop Research and Organic Weed Control’ and included side-discussions and presentations on other related research projects our group is doing with cover crops at the University. This opportunity provided me with a platform to give a 20 minute presentation on the importance of native pollinators, why we should conserve them in agricultural landscapes, and how we can consider the use of flowering cover crops as a dual purpose crop for field-level agronomic and ecosystem service conservation benefits. Several of the famers that I spoke with at this event seemed genuinely interested in helping our native pollinators I believe my presentation peaked their interest in considering what other benefits can be gained from smart cover crop plant choices. The second extension field day event took place on September 11, 2013 at the Penn State research farm. This event was a collaborative event between our Penn State cover crop research team and the Pennsylvania Association for Sustainable Agriculture (PASA). The topic of this event was ‘Cocktails & Crimpers: Cover Crop Innovations for Low-Input Soy, Corn & Wheat Production’, but again I was able to speak to this audience for about 20 minutes about pollinators and using cover crops for their conservation benefit. Both field day events went very well and were met with interest and enthusiasm from many of the participants. Also included at the conclusion of both field days were evaluation questionnaires of the event. For this I incorporated questions that gave me information regarding the participant’s previous knowledge of native pollinators, knowledge gained via my presentation, and future interest in planting flowering cover crops for the use of native pollinator communities. We had a total of 41 participants between both field days. Combining the evaluations from both events, 61% of the participants reported leaving with increased knowledge of native pollinator diversity, 61% said that they would likely consider planting cover crops for the purpose of pollinator conservation, and 59% said they were now more likely to allow cover crops to flower for pollinator use.
     An extension publication detailing some of the results from this study and how these results translate into grower recommendations on using flowering cover crops for pollinator conservation purposes is forthcoming and will likely be published in early 2014.


Dr. Mary Barbercheck

[email protected]
Professor of Entomology
Penn State University
501 ASI Building
University Park, PA 16802
Office Phone: 8148632982