Optimal Timing of Hive Placement for Wild Blueberry Pollination

Thursday 23 February 2023

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!

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.

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