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

View the project final report

Commodities

• Fruits: berries (blueberries)
• Animals: bees

Practices

• Crop Production: pollination, pollinator habitat

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.

Final Report: 1) The project addressed the long standing concerns of farmer collaborators associated with southern high bush blueberry in the Southeastern US, particularly in Florida. Farmers have continually pursued strategies to improve pollination outcomes but have often encountered difficulties and insufficient results. This project set out to examine the effects of two managed pollinator species (honey bees (A. mellifera)and common eastern bumble bees (B. impatiens)) in tandem. Both species have been examined independently in the system but their cumulative and/or synergistic effects on blueberry pollination had not been studied. Previous findings (Mallinger et al. 2021) showed that the presence of managed bumble bees significantly and drastically improved pollination outcomes. This finding underscored the value of managed bumble bees but it was unclear how their impact was associated with honey bee presence. In this study all farmers that utilized bumble bees used them in conjunction with honey bees. This meant that it was unclear how bumble bee mediated benefits occurred. Were these benefits a result of bumble bee pollination solely or was their presence also capable of improving honey bee efficacy through increased pollen flow in the system and direct interactions between bees on flowers that lead to more movement? 2) The research approach of the project was to utilize a cage set up with two treatments of pollinators present with 60 mature blueberry bushes. The treatments were a honey bee only treatment that replicated the non-buzz pollinator system that has been historically utilized by blueberry farmers and a honey bee plus bumble bee treatment that replicated the new approach to managed pollinators being adopted by many farmers. This design allowed us to analyze the pollinator visit and yield metrics associated with each treatment and examine what impact the presence of bumble bees had on honey bee visitation, efficacy, and behavior as pollinators. Our educational approach and farmer learning outcomes were primarily achieved via targeted research and extension talks to local shareholders, an extension document highlighting the benefits of bumble bee utilization, and workshops associated with producer organizations. These cumulative efforts and collaborations with extension professionals at UF allowed for the management practices and findings of the project to be seen by dozens of farmer collaborators. Our goal associated with farmer learning outcomes were to educate farmers on the benefits of implementing bumble bees and how their behaviors improve pollination and have been shown to interact with honey bee efficacy. We also set out to improve farmer management associated with managed bumble bees. This primarily focused on when, where, and how to place bumble bee colonies in the field and how what to expect of them as flower visitors. 3)This research found that the presence of bumble bees with honey bees does alter foraging behaviors as a result of direct interactions. When both species are present, we saw significantly more interactions that caused for greater movement across plants within the experimental cages. In an open field setting this kind of interaction has been shown to improve cross pollination and yield as a result. We also found that bumble bees are more frequent visitors and provide better value when farmers plan to bolster pollination services with honey bees already occurring at recommended stocking densities. Data associated with increased honey bee pollen contact in the presence of buzz pollinating bumble bees is being finalized. However, after one season of data we found no evidence that honey bees collect or carry more pollen in the presence of bumble bees. We did find that in cage settings honey bees are capable of collecting blueberry pollen, which is infrequent in open field settings. This finding could mean that through improved breeding and management practices that honey bee efficacy could be improved by allowing for greater pollen foraging frequency. These findings provide clear evidence that bumble bees are an effective pollinator that have the potential to synergistically improve honey bee efficacy when both species are present in blueberry fields. 4) The farmer adoption outcomes that we observed were incremental increases in the number of farmers implementing managed bumble bees, higher stocking densities among those that already utilized them, and better management practices to optimize them. Examples of better management practices were farmers placing bumble bees in advantageous places in the farm such as inside of high tunnels. This places the bumble bees closer to the targeted crop and reduces the chances of honey bee robbing behavior. Farmers were also instructed to remove and properly dispose of colonies at the end of bloom. This was undertaken by farms observed by the research team and can lead to reduced risk of pathogen spill over in native bee populations. 

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.