What’s the Buzz? Assessing Efficacy, Synergisms, and Sustainability of Pollinators in Southern Highbush Blueberry (Vaccinium  corymbosum  L.) 

Progress report for GS21-244

Project Type: Graduate Student
Funds awarded in 2021: $16,493.00
Projected End Date: 08/31/2023
Grant Recipient: University of Florida
Region: Southern
State: Florida
Graduate Student:
Major Professor:
Rachel Mallinger, Dr.
University of Florida
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Project Information


Southern highbush blueberry (Vaccinium corymbosum L.) is highly dependent upon insect pollination with fruit set and berry weight both decreasing dramatically in the absence of pollinators. Due to this, the abundance and efficacy of pollinators is closely tied to successful blueberry production. In Florida, previous research has shown that wild pollinator visitation rates are low. This leaves growers reliant on managed honey bees (Apis mellifera L.), and still often receiving unsatisfactory pollination due in part to honey bees limited efficacy as blueberry pollinators. Bumble bees (Bombus impatiens), which are capable of buzz pollinating and can be stocked as managed pollinators, have been shown to be more effective pollinators; we found that increasing bumble bee stocking density improves fruit set and yield despite low overall visitation rates as compared to honey bees, indicating a disproportionately positive impact on blueberry pollination. However, the use of these two managed pollinators together to achieve optimal pollination has not been well studied despite the growing proportion of farmers who invest in both pollinators during bloom. The objective of this study is to test the hypothesis that managed bumble bee deployment facilitates and improves the efficacy of non-buzz pollinators by increasing rates of pollen release. Additionally, southern highbush blueberry breeding selections will be assessed to determine their attractiveness to buzz pollinators including their pollen quantity and release rates. The proposed research will provide a better understanding of whether utilizing both managed bumble bees and honey bees together is an economically sustainable approach to improving blueberry pollination.


Project Objectives:

Objective 1: Assess synergy between buzz pollinators and honey bees. The first objective will focus on the pollen deposition of honey bees both in the presence and absence of buzz pollinators. This will provide insight into the mechanisms by which honey bees are able to encounter and deposit blueberry pollen. We know that honey bees are depositing small amounts of pollen when visiting blueberry flowers, even during nectar foraging (Rogers et al. 2013, Benjamin and Winfree 2014). However, it is not clear how they are coming into contact with pollen and what role previous visitors, including buzz pollinators, are playing. Are honey bees able to release pollen on their own despite their inability to buzz pollinate or are they encountering pollen as a result of previous buzz pollination? If the latter mechanism is correct, then the presence of buzz pollinators would likely have a synergistic impact on pollination by increasing pollen release and facilitating honey bee pollination efficacy.

Objective 2: Evaluate pollen quantity and release rates across blueberry genotypes. The second objective will assess how breeding selections vary in pollen quantity and release when buzz pollinated. This will provide a framework for assessing what breeding selections could receive optimal pollination services from both buzz and non-buzz pollinators. We predict that cultivars will vary in their total available pollen quantity as well as the release rate of pollen that occurs in response to buzz pollination. These two factors in combination would influence the amount of pollen that visitors would encounter, thereby influencing both pollinator recruitment and pollen transfer. In collaboration with the Blueberry Breeding Program at UF, we will be able to highlight certain selections to inform future breeding efforts. This outcome would provide producers with cultivars that exhibit greater pollination success.

Objective 3: Examine the influence of floral traits on pollinator visitation and behavior. Finally, the third objective will examine the influence of these pollen traits including pollen quantity and release rates on pollinator recruitment and pollination efficacy. If these traits are in fact impacting pollinator recruitment and behavior, they could play a key role in pollen transfer and pollination success.. These understudied traits could play an important role in the attraction and effectiveness of pollinators and represent an area of interest for plant breeding to improve pollination. Examining variation across selections in pollen quantity and release will enhance our understanding of why growers report differences in fruit set and yield across cultivars as well as improve our understanding of the efficacy of pollinators.


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  • Dr. Patricio Muñoz (Researcher)


Materials and methods:

Obj. 1: Synergisms Between Buzz and Non-Buzz Pollinators

            To assess the impact of buzz pollinators on honey bee pollination efficacy, I will examine pollen deposition by honey bees with bumble bees present and absent. To accomplish this, four paired large-scale blueberry high tunnel production sites will be used. The high tunnel setups will have identical stocking densities of honey bees with colonies placed outside of the tunnel with the end open to allow visits. One of the high tunnel sites per pair will receive additional managed bumble bee colonies at a density of approximately 1 quad (4 individual colonies) per acre placed inside of the tunnel (Koppert Biological Systems). At both sites, pollinators will be allowed to forage on blueberry flowers. After approximately 2 hours of active foraging within the high tunnels a minimum of 15 honey bees actively visiting blueberry flowers will be collected in each treatment per sampling date. Sampling will be replicated twice-weekly for a minimum of 6 times across the bloom period. Honey bees will be collected and individually placed in Eppendorf tubes on ice as they forage in the high tunnels. Upon returning to the lab, bees will be placed in a freezer until they are ready to be processed. Processing will begin with honey bees being dried for 96 hours at 40°C and then stored at room temperature. Honey bees will then be individually washed using a solution of 12 mL of saline with 100 µL of a 0.1% aqueous solution of malachite green stain (Vaissiére & Froissart 1996). The solution with the bee will be ultrasonically probed for 60 seconds to remove all pollen from the body of the honey bee. This washing method will be repeated to ensure that all pollen is successfully removed (Vaissiére & Froissart 1996). Blueberry pollen grains will then be identified, counted, and compared across the two treatments (with and without bumble bees) to test the prediction that bumble bees will increase the amount of blueberry pollen that honey bees encounter and transfer while foraging. Pollen present on honey bees will be analyzed using a t-test to compare the effect of bumble bee presence. Additionally, 10 bagged branches within each paired high tunnel will be observed for honey bee per visit pollen deposition within a standard genotype. Following a single visit by a honey bee to a flower, the stigma will be collected, and pollen grain deposition will be assessed following the above protocols. We will determine if the presence of buzz pollinators improves honey bee per-visit pollen deposition.

Obj. 2: Variation in Floral Traits Across Plant Genotypes

            Pollen availability and release will be assessed in 40 breeding selections cultivated by the UF Blueberry Breeding Lab in Waldo, Florida. To assess this, 10 flowers from each breeding selection will be buzzed by a handheld buzz pollination tool (VegiBee Garden Pollinators) on the highest frequency setting. Buzzes will closely match observed buzz duration of bumble bees by buzzing flowers for 3 seconds. Newly opened flowers will be selected on previously bagged branches to ensure that the flower had not been previously visited by a pollinator.  While artificially buzz pollinating, pollen grains will fall into microcentrifuge tubes. This will tell us the amount of pollen released per buzz. The buzzed flower will also be collected to assess how much pollen remains following a buzz and the total pollen quantity per flower across breeding selections. Following collection, pollen and flowers will be stored in a freezer until processing, at which point they will be dried at 40°C for 24 hours (Vaissiére & Froissart 1996). Once dried, flowers will have their anthers removed and dissected to ensure that all remaining pollen is released. After dissection, the anthers will be placed back in individual tubes with the remaining flower material. Pollen will be washed from flower material following the same protocol as described above for honey bees (Vaissiére & Froissart 1996). Buzzed pollen grains will be stained using malachite green stain. Pollen release and quantity will be assessed by counting pollen grains under a microscope. This objective has been completed in 2021, but lab processing and data analysis has not been completed as of the time of submission. Pollen quantity and release via sonication will be replicated in 2022 and 2023. Analysis will be conducted using ANOVA with pollen release rate and total pollen quantity as dependent variables and breeding selection identity as an independent variable.

Obj. 3: Floral Trait Effects on Pollinator Recruitment and Behavior

            Pollinator behavior observations will take place at the UF blueberry breeding plot in Waldo, Florida. The breeding plot is a mixed planting that includes plants of all 40 focal breeding selections. Managed buzz pollinators will be stocked at current recommendations (4 bumble bee colonies per acre) and allowed to forage throughout the plot. Pollinator visitation and behavior data will be taken on all 40 selections. Observations will take place a minimum of 3 times weekly for the duration of the flowering period of each breeding selection with a total of two 1-minute long observations per selection per sampling date. The number of flower visits for honey bees, bumble bees, and other flower visitors will be recorded along with the number of flowers present on the bush. Behavioral responses such as buzz pollinating and nectar foraging will be recorded. These behavioral responses and visitation rates will be compared across breeding selections and compared with the results of pollen quantity and release rate per selection. This protocol has been completed for the 2021 blueberry season but has not been analyzed as of the time of submission. Pollinator sampling will be replicated in 2022 and 2023. Data will be analyzed using linear mixed effects models with pollinator visitation variables treated as dependent variables and selection as an independent variable, Julian date and weather data will be included as random effects. This analysis will provide evidence of the role that floral traits such as pollen quantity and release play in pollinator behavior.


Research results and discussion:

The first field season associated with the grant is expected to be completed in April. Once this is completed we will complete associated lab work and data analysis that will allow for results to be presented. In the first season we completed the first year of objective 1 successfully. During this period, honey bees foraging in the presence and absence of bumble bees were collected and will be analyzed for pollen on their bodies. This will provide us with evidence of any facilitation through pollen release that bumble bees provide for honey bee pollination. Additionally, fruit set and yield data was/is being collected that will provide evidence of the benefits of a mixed bumble bee and honey bee stocking compared to honey bee only. Pollinator visitation to blueberry flowers was also completed to assess the behavior of these two species of managed pollinators. Finally, blueberry flower stigmas were collected and will be analyzed to assess pollen deposition across our treatments. 

All research associated with Objectives 2 and 3 were also completed in March and lab activities will be completed in the upcoming months. Once this process is finalized, all data will be added to data collected in 2021 and analyzed.

In the field season completed in year 1 of the grant all projects were completed as planned and are on track. 

Participation Summary
1 Farmer participating in research

Educational & Outreach Activities

4 Webinars / talks / presentations
1 Other educational activities: We participated in a tabling event at the Flora and Fauna festival. We educated the general public on the importance of pollinators in agriculture, the kinds of bees they may see and the differences in their behavior, and how to help conserve pollinators.

Participation Summary:

10 Farmers
40 Ag professionals participated
Education/outreach description:

The above activities have been primarily focused on educating farmers and beekeepers about the pollination benefits associated with different species of pollinators and how to effectively implement managed pollinators into blueberry production. This has been done through extension presentations targeted at primarily beekeepers. Upcoming talks focused on blueberry farmers are planned with one occurring in Quincy, FL in April. In addition to our work with agricultural professionals, similar activities were completed at an outreach event targeted at the general public where 100+ people were reached. To this point, our extension/outreach efforts have primarily focused on teaching about the benefits of pollinators and the differences between them as we have not yet completed our first field season associated with the grant. This first feels season will be completed in April and data analysis and lab work associated with the research will follow. Once that is completed, newsletters and more presentations will be completed to early disseminate results. 

Project Outcomes

Project outcomes:

The first field season of the grant is being completed. Project Outcomes will be updated as they are completed.

Knowledge Gained:

The first field season of the grant is being completed. Project Outcomes will be updated as they are completed.


The first field season of the grant is being completed. Project Outcomes will be updated as they are completed.

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.