There is a high demand for pollinating honey bee units on wild blueberry fields in Atlantic Canada. Aside from increasing colony numbers, the industry can meet this demand by optimizing the use of existing honey bee units for maximum efficiency during the wild blueberry bloom period. ATTTA field research has been focused on this objective during our last five years of summer field work. One important management decision in regard to pollination services is when to deploy hives for pollination. In this blog, we will discuss our research findings and our suggestion on optimal timing of hive placement.

Optimal Timing of Hive Placement for Wild Blueberry Pollination

Longstanding, conventional practice is to place honey bees for pollination on blueberry fields when bloom reaches 10-20% open flowers. The stocking density recommendation is up to three hives per acre. Hive rotation and sequential loading during blueberry bloom are currently being practiced by a limited number of producers in our region. Sequential loading involves increasing and decreasing stocking densities of honey bee colonies to reflect changes during the bloom period. As the percent of open flowers on a field increase, the theoretical requirement for pollination will increase.  The desired result of this practice is to achieve optimal pollination through enhanced efficiency in the use of honey bee colonies. 

In the 2022 field season, ATTTA studied the impacts of hive placement on pollination success. Using a limited number of trial fields across the Maritime region, we found that deploying hives during early bloom has significantly positive impact on pollination success, measured by fruit set. Figure 1 below demonstrates this impact, where the percent of successful fruit set decreases as the percent bloom at time of hive placement increases. 

Figure 1. Linear relationship between fruit set and percent bloom at time of pollination. Red line indicates negative relationship, grey shading indicates the area between the error lines.

Foraging behaviour of honey bees on wild blueberries is little understood. However, it has been long suggested that honey bees placed on blueberry fields too early in the bloom period may habituate to other floral sources, abandoning the yet unopened blueberry flowers. There are complexities about honey bee behaviour (Abou-Shaara 2014) which indicates that previous thinking about the determent of early placement on honey bees is outweighed by the loss of production when pollination begins late, after 10-20% bloom. ATTTA field work results suggest that after 50% bloom the opportunity for optimized pollination and subsequent fruit set may be significantly lowered. The impact on yield of delayed pollination, and therefore income for the producer, may be significant. 

Another striking result of our field work from 2021-2022 shows a trend of honey bee hives are being placed on fields late into the bloom period. Figure 2 below shows that the average percent bloom when honey bees are place for pollination is 47.12%! This does not support effective pollination, and we urge producers to assess their fields for percent bloom in the upcoming season to determine, more precisely, the optimal time for placement of bees. 

Figure 2. Percent bloom assessed within 24 hours of hives being placed on blueberry fields (n=18) in the 2021-2022 seasons. Whiskers = standard deviation.

Percent bloom can be assessed by counting open and closed flowers on a select stem and applying the following formula. 

% bloom = (open flowers / all flowers) x 100

It is best to count several stems and take the average % bloom for a broader field representation. UMaine Cooperative Extension has further information on how to assess individual wild blueberry fields for pollination requirements. 

Best practice for optimal and efficient hive use may be to place bees at a lower stocking density as blossom is opening, from 1-10% bloom, and increase hives to full stocking density at 25% bloom. It seems that the detriment of possibly placing hives too late in the bloom period outweighs those of placing hives too early. Better too early than too late!

References
Abou-Shaara, H.F. 2014. “The Foraging Behaviour of Honey Bees, Apis Mellifera: A Review.” Veterinární Medicína 59 (1): 1–10. https://doi.org/10.17221/7240-VETMED.

Connecting with ATTTA Specialists

If you’d like to connect with ATTTA specialists or learn more about our program, you can:

visit our website at https://www.perennia.ca/portfolio-items/honey-bees/

Email abyers@perennia.ca

Atlantic Canada is known for its delicious, locally grown wild blueberries. However, growing blueberries can be complicated, and relies on pollinating insects such as honey bees. In this blog, we will discuss wild blueberry flowers and how they are pollinated. We will also give a quick update on ATTTA’s wild blueberry research and the next steps in one of our exciting projects. 

Pollination of Wild Blueberries

Each individual wild blueberry plant is called a clone and can grow to around knee height. The leaves are overt and oval-shaped with smooth edges. The flowers grow in clusters and the corolla (petals) take on a bell shape with greenish-white or pinkish coloring. Protected inside the flower are multiple stamens containing anthers that hold pollen (male reproductive cells). At the base of the flower are the ovary and ovules. Extending out of the flower is the style that ends at the stigma. Due to the shape of the flower, wind is not considered a pollinating factor.  This means insects are the only way pollination can occur.

Figure 1: Diagram of cross-section wild blueberry flower in bloom (Image: Drummond, 2019)

Figure 2: Honeybee on wild blueberry flower (ATTTA©2022)

During the wild blueberry bloom in warm months of May and June, the stigma responds to movement created by attracted insects causing the anthers to release pollen. Therefore, when a honey bee or bumble bee visits a flower, released pollen attaches to their body hairs to be transported to subsequent flowers they visit. This transport is essential as it distributes male reproductive cells from one individual blueberry plant to another.  This allows for the reproduction of the plant and the forming of fruit. After an individual flower has reached the end of its blooming period, the petals fall off, leaving the green ovary and ovules. If pollinated adequately, the process of fruit set will begin as the ovary matures into seeded fruit. It starts with bloating of the ovary as a small, round, white-green fruit, ripening to a dusted blue shortly afterwards. 

Figure 3. Fruit set after successful pollination and resulting from the swelling of the ovary, immature fruit is shown as well as one ripe blue berry (ATTTA©2022)

Pollination is key to fruit set on wild blueberries, making it essential to have an abundance of pollinators on blueberry fields. Here in Atlantic Canada, honey bees and bumble bees are commonly tasked with this critical job. Managed honey bee colonies are easily added to fields, bringing an abundance of pollinating capacity. Colonies brought in should be appropriately strong and ideally provide at least one forager bee per square yard (Drummond. 2002). This will, among other factors, help determine the stocking density of honeybee colonies needed for individual fields.  

Honey bees provide adequate numbers to pollinate multiple blueberry flowers and have small bodies that can get inside the bell-shaped flower and shake the pollen loose. Managed or native bumble bees are phenomenal and unique pollinators, as well. Their size and buzzing ability effectively shake out pollen and distribute large quantities from one clone to another. Their extra-long tongues allow them to access and pollinate some of the more closed-off flowers that honey bees may not be able to reach. They are also more resilient to pollinating across a broader range of weather conditions. In spite of being less efficient individually, honey bees have the sheer numbers to pollinate many flowers.

Now that the fruit is beginning to develop on blueberry fields, the Atlantic Tech Transfer Team for Apiculture will be continuing with one of our ongoing pollination projects. In May, we visited wild blueberry fields in NB, NS, and PE to assess honeybee hive strength and percent bloom.  In the upcoming weeks, we will return to these fields and evaluate the number of open blooms which have transformed into fruit.  This determination is called fruit set and is an indication of pollination success. This measure in addition to others, such as number of berries at harvest, fruit weight and seed counts, allows us to evaluate the impact that honey bees have ultimately on the final yield.  Stay tuned for updates on this work as the season progresses! 

Written by Rebecca Campbell, ATTTA Summer Research Assistant rcampbell@perennia.ca

References
Drummond, F.A. 2019. Over-informed on IPM - Episode 006: Wild Blueberries and Their Wild Pollinators. University of New Hampshire. https://extension.unh.edu/blog/2019/05/over-informed-ipm-episode-006-wild-blueberries-their-wild-pollinators.
Drummond, F.A. 2002. Honeybees and blueberry pollination. University of Maine Coop. Ext. Wild Blueberry Bulletin No. 629.

Connecting with ATTTA Specialists

 

If you’d like to connect with ATTTA specialists or learn more about our program, you can:

 

visit our website at https://www.perennia.ca/portfolio-items/honey-bees/

 

Email abyers@perennia.ca