Investigating techniques for successful overwintering of honey bee queens in bulk

Progress report for OW20-356

Project Type: Professional + Producer
Funds awarded in 2020: $49,796.00
Projected End Date: 08/31/2023
Host Institution Award ID: G121-21-W7901
Grant Recipient: Oregon State University
Region: Western
State: Oregon
Principal Investigator:
Dr. Ramesh Sagili
Oregon State University
Ellen Topitzhofer
Oregon State University
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Project Information


Beekeepers in the United States have reported high colony losses for more than a decade. Among many stress factors experienced by honey bees, beekeepers report queen failure as one of the highest contributors to colony loss. Beekeepers can effectively reduce the rates of colony mortality in their apiaries by replacing failing queens, which are available through queen producers. Beekeepers assess their colonies in January and February in preparation for almond pollination services in California. Accompanied by high colony losses, beekeepers may struggle to fill their pollination contract commitments with healthy queenright colonies.

Reports on management practices suggest that the rate of queen replacement by U.S. beekeepers has drastically increased in recent years. This heavy increase in demand for new queens warrants exploring solutions to increase queen supply. One available technique involves overwintering queens in "bank" colonies. For this technique, beekeepers purchase late-season queens and suspend them inside a single bank colony during the winter. After winter, beekeepers can use these queens to replace failing queens in colonies prepared for almond pollination services or introduce them into newly divided colonies after the almond bloom to offset winter colony losses.

We proposed to investigate the technique of overwintering honey bee queens in bank colonies with Oregon beekeepers that pollinate almonds in California. We overwintered queens in bank colonies with three commercial beekeeping operations (September 2020 – January 2021). Bank colonies were assessed for strength (frames of bees, frames of brood), amount of stored honey, and pest and pathogen levels (Varroa mites, Nosema spp.). We sampled queens from these bank colonies for morphometric and reproductive metrics and will compare results from queens confined in banks with unconfined queens from established colonies. We also introduced banked queens into new colonies at the end of the almond bloom, and their performance will be assessed throughout the year (March 2021 – January 2022). Preliminary results from bank colony assessments and queen survival data will influence our project goals for next winter, including determining optimal queen placement in bank colonies, validating pest and pathogen pre-screening methods for candidate bank colonies, and improving bank colonies by increasing colony strength in September.

Project Objectives:

Our goal is to evaluate the technique of overwintering queens in bank colonies for beekeepers in Oregon. We posed some research questions regarding this technique: will overwintering queens in bank colonies for approximately 4-5 months effect their reproductive potential? How will these queens perform compared to standard early-season sourced queens? What is the optimal positioning for queens inside bank colonies to maximize winter survival? We will continue evaluating this technique for the next two winters. The following is the progress pertaining to the study:

  1. We determined the percent survival rate of queens overwintered in bank colonies with three commercial beekeeping operations in Oregon (September 2020 - January 2021).
  2. We sampled queens that overwintered in two situations: a) confined in bank colonies and b) unconfined in established colonies (January 2021). We will analyze these queens for morphology, total sperm count, and sperm viability.
  3. We introduced queens that overwintered in bank colonies into newly established colonies after the almond bloom in California (March 2021). We will evaluate the performance of these queens throughout the year alongside early-season sourced queens. Performance metrics include queen supersedure events, brood pattern quality, and brood disease prevalence.

Refer to the two attachments of a Gantt chart for a timeline covering all project objectives.

  1. .xlsx file attachment: WSARE_Gantt_Chart_xlsx
  2. .pdf file attachment: WSARE_Gantt_Chart_pdf



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Materials and methods:

The research team (PI, co-PI, and five producers) determined necessary attributes of bank colonies based on published research findings and personal experiences. We also agreed on a bank frame design that holds 20 queens. In September and October 2021, we constructed five bank colonies with three producers, each residing in different regions of Oregon. We assessed every colony in one of the producers’ highest performing apiaries and chose five candidates to serve as bank colonies based on criteria from our discussion. We placed 20 experimental queens in each of the five bank colonies. An additional 32 colonies were assessed in the same apiary to serve as control colonies. The original queen was removed from each control colony and replaced with an experimental sister queen. Queen survival was determined in bank colonies before and after transit to California in January.

The research team actively managed the bank colonies during placement in California. The management process involved introducing two full frames of brood every two weeks. These brood frames were assessed 7-8 days later for queen cells, and all queen cells were destroyed. We recorded total frames of bees for each bank throughout the management process.

After approximately two weeks in California, queens were sampled from bank colonies and control colonies (n=20) and sent to North Carolina State University’s Honey Bee Queen and Disease Clinic and will be analyzed for morphology, total sperm count, and sperm viability. We successfully replaced each queen sampled from control colonies.

Research results and discussion:

Bank colonies had the following attributes when the queens were introduced.

  • Double-story (2 boxes) hive configuration
  • 14-19 frames of bees
  • Approximately 70 pounds of stored honey
  • No laying queen present
  • Technician assessed brood 7-8 days later for queen cells; cells were destroyed

As the table illustrates, there was wide variation in queen survival among bank colonies and beekeeping operations. However, we observed high queen survival for banks during transit to California. Based on observations from January 30 – March 8, all bank colonies satisfied the minimum colony strength requirement recommended for almond pollination (four frames of bees). However, not all bank colonies satisfied the average strength recommendation of eight frames of bees.

Beekeeping Operation Average Queen Survival (%) Range (%)
BK1 86 55-100
BK2 78 67-95
BK3 34 0-90


Participation Summary
5 Farmers participating in research

Educational & Outreach Activities

1 Webinars / talks / presentations

Participation Summary:

Education/outreach description:

We presented preliminary results from this project at the British Columbia Honey Producer Association’s Semi-Annual Education Day on March 21, 2021. Approximately 130 beekeepers attended this presentation.

Project Outcomes

Project outcomes:

Both current and future results from this project can be used to increase the sustainability and profitability of the Pacific Northwest beekeeping by reducing colony loss during almond crop pollination. This study also has potential to reduce risk of poor pollination due to healthy honey bee colonies, therefore increasing agricultural crop yield that requires bee pollination. We already received tremendous support for researching the technique of overwintering queens in bank colonies in Oregon. Active producer participation and widespread interest in this project bolsters strong potential for industry adoption of this technique.


We do not have any final recommendations yet, but we have collected valuable data that will help us refine the current methods. Project improvements include determining optimal queen placement in bank colonies, validating pest and pathogen pre-screening methods for candidate bank colonies, and improving bank colonies by increasing colony strength in September.

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.