Variety Is Key

Managed Bumble Bees Are a Great Way to Bolster Pollination

Are they right for me?

Managed bumble bees are a great option for supplementing existing pollination on blueberry farms. Bumble bees are especially valuable in cases where pollination problems such as insufficient fruit set, underperforming cultivars, and poor pollinator visitation are occurring. Due to their differing behaviors, higher pollination efficacy, and extended foraging compared to honey bees, managed bumble bees may act as a biological insurance policy. 

Having a diverse assemblage of bees present on blueberry farms is the best way to ensure sufficient pollination. This can be accomplished by promoting native bee populations as well as stocking both managed honey bees and bumble bees. Bumble bees are capable of buzz pollinating, a behavior that allows them to vibrate flowers and induce the release of more pollen. The ability to buzz pollinate is among the primary factors that make bumble bees more effective per visit than honey bees, depositing over 3x more pollen per visit (Sun et al. 2021). Bumble bees also visit more flowers per minute of foraging and are actively foraging for longer periods each day (Sun et al. 2021). They are also capable of foraging in weather conditions that honey bees do not. Managed bumble bees have also been shown to be more reliable pollinators in covered settings such as high tunnels and greenhouses and are recommended for those production systems. 

Previous research at the University of Florida found that increasing stocking density of bumble bees on blueberry farms in Florida led to increased bumble bee visitation and crop yield (Mallinger et al. 2021). Meanwhile, similar increases in honey bee stocking density far above recommended rates did not reliably improve honey bee visitation or crop yield (Mallinger et al. 2021). These results indicate that bumble bees can be an effective strategy to boost pollination. If blueberry farmers are still dissatisfied with pollination when honey bee stocking densities are met, they may be better off investing additional money into managed bumble bees rather than stocking honey bees at rates exceeding recommendations. Managed honey bees remain the primary way for farmers to secure pollination services, but bumble bees can act as a valuable supplement when the recommended honey bee stocking rate has already been met. 

A bee on a flower

Description automatically generated

Image 1: A Common Eastern Bumble Bee (Bombus impatiens) visiting a flower on a Florida blueberry farm.

What are they?

The Common Eastern Bumble Bee (Bombus impatiens) is a bumble bee species native to the Eastern United States (Image 1). These bumble bees can be found nesting belowground with over 450 individuals at their peak colony size (Michener 1974). Within their native distribution, they can be found in all habitat types and are generalist pollinators that will collect pollen and nectar from a wide variety of flowering species. Like honey bees, bumble bees are social insects with colonies made up of a queen that reproduces and worker bees that care for offspring and collect resources for the colony. These features make bumble bees excellent pollinators and highly valuable for crop production. This value has led to bumble bees being reared for commercial use, where they can be placed in targeted cropping systems throughout the year. Within their native range in the Eastern U.S., these bees can be placed in open field settings as well as high tunnel and greenhouse production systems.

How to get them?

There are two primary suppliers of managed bumble bee colonies for crop pollination — Koppert and Biobest. Each of these companies offers several bumble bee products, but the most used and best value option for crop pollination is the “Quad” or “4-Pak Hive” for each respective company. These boxes contain four separate bumble bee colonies of approximately 250 workers each. The duration of the colony will vary based on crop and environmental factors but a minimum of 6 weeks of pollination services should be expected. Orders should be placed at least three months in advance to ensure that bees will be available in the desired quantities as blueberry bloom approaches. Recommended stocking densities have not yet been published for Florida blueberry production. However, most growers utilizing bumble bees stock them at a rate of 1 “Quad” or “4-Pak Hive” per 2-5 acres of crop (Mallinger et al. 2021). The recommended date of delivery will vary based on the environmental conditions and cultivars present, but it is recommended to place bumble bee hives at the beginning of crop bloom. Orders can be pushed back to better match crop flowering, but any adjustments should be made at least a week in advance of the previously scheduled delivery date. All hives will be shipped overnight to arrive on the scheduled delivery date. When bees are delivered, it is best to place them in the field as soon as possible so they aren’t left outside in direct sunlight, rain, or strong winds for extended periods of time. 

How to use them?

Placement in the field is very important to attain optimal pollination services. In open field settings, bumble bee colonies should be placed adjacent to or within the focal blueberry crop. Bumble bees will most frequently visit fields with flowering crops that are nearby and are less likely to visit distant fields. For this reason, especially on larger farms, it is best to place bees evenly throughout the plot or on each edge of a focal field instead of placing all boxes in one location. In high tunnel settings, boxes can be placed inside of the tunnel with the hive doors parallel to the crop rows. It is also important to place bumble bees in a different location than any honey bee hives that are present with at least 100 yards separating them if possible. Honey bees have been observed entering bumble bee colonies, likely in search of collected floral resources. These interactions may cause reduced pollination services and reduced bumble bee colony survival in extreme cases.

Once a suitable location is selected, bees should be placed on a horizontal platform elevated off the ground to avoid water and pests from entering the box. Palettes or concrete blocks are good options to elevate boxes. In both cases, a large stone or brick should be placed on top of boxes so that they don’t blow away. It is also recommended to provide the box with cover to avoid direct sunlight and rain (Image 2). On days where the ambient temperature is above 77°F, shade is necessary to keep the colonies from overheating. A piece of corrugated plastic sheet acting as a sloped roof or tented structure above the box is sufficient for providing shade. While this is recommended, it is not as crucial to bumble bee colony health during blueberry bloom due to the cooler temperatures and the water-resistant material of the boxes. In other cropping systems where pollination is needed when the ambient temperature is higher, shade structures are required for optimal results.

Once boxes are placed in the field you should wait at least 30 minutes before releasing the bees. This will allow for them to calm down from the stress of being shipped and moved. Bees can be released by setting the doors on each of the four colonies to “in and out.” The “in and out” setting will allow bees to enter and exit the hive normally and provide pollination services. If boxes must be moved during the season, gloves and protective clothing are recommended. Prior to moving boxes, the plastic doors can be set to “in-only” and bees will be able to return to the colony but won’t be able to exit again. After 2 hours, nearly all bees that were away should have returned and the colony can be safely moved in the evening. However, moving colonies after initial placement is not recommended and can lead to increased risk of stings. 

At the end of the season, it is crucial that bees are properly disposed of as escaped bees could pose a risk to native bumble bee populations. At the end of crop bloom and no later than 12 weeks post-placement, all doors should be set to “in-only” and subsequently closed. Hives should then be sealed in large plastic bags for 2 weeks or frozen for a week to kill all remaining bees. Once all bumble bees are dead, colonies should be disposed of according to local legislation. 

Image 2: The recommended structure for a Quad or 4-Pak Hive of managed bumble bees. The palette keeps the box off the ground while the corrugated plastic sheet provides shade and rain cover. 

Are they working?

Yes, research has shown that managed bumble bees are effective in Florida blueberry production. It is common for blueberry growers that purchase managed bumble bee colonies to wonder if they are working. This is due to several factors that play into the reason that they are good pollinators in the first place. Bumble bees live in smaller colonies and are stocked at rates much lower than honey bees; this means that you are less likely to see them as you walk through the field. They also move between flowers faster than honey bees, making them more effective pollinators but also harder to spot. In addition to these factors, bumble bees are also capable of foraging in weather conditions where honey bees are not foraging. On cool mornings or drizzly afternoons when honey bees are in the hive, there are likely still bumble bees foraging. This added pollination is very valuable for fruit set and yield, especially when poor weather conditions persist for several days in a row. Although pollination at these times is valuable it is easily overlooked because growers are not looking for bees in poor weather conditions. When purchasing managed bumble bees, it is important to recognize that the differences in their behaviors make them a great supplement to honey bees, but it is also more challenging to observe their contributions in real time. Despite this, research has shown that managed bumble bees are a great way for Florida blueberry growers to bolster pollination.

CREDIT
John J. Ternest, PhD Candidate, University of Florida, Entomology and Nematology Department

Sources Cited

Mallinger, R., Ternest, J. J., & Naranjo, S. M. (2021). Blueberry Yields Increase with Bee Visitation Rates, But Bee Visitation Rates Are Not Consistently Predicted by Colony Stocking Densities. Journal of Economic Entomology114(4), 1441-1451. https://doi.org/10.1093/jee/toab111

Michener, C. D. (1974). The Social Behavior of the Bees: A Comparative Study. Harvard University Press.

Sun, Q., Zhao, X., Wu, L., Zhao, J., Yang, Y., & Zhang, Y. (2021). Differences in Pollination Efficiency Among Three Bee Species in a Greenhouse and Their Effects on Yield and Fruit Quality of Northern Highbush ‘Bluecrop’ Blueberry. HortScience56(5), 603-607. https://doi.org/10.21273/HORTSCI15714-21

Share this post:

Comments on "Variety Is Key"

Comments 0-5 of 0

Please login to comment