Counter to conventional thought, research has shown that clumping hives away from row edges has no detrimental effect on honeybee visitations to blueberry fields and in fact increases bee visitations.

Lisa Wasko DeVetter

Speaking at the Oregon Blueberry Conference February 4 in Salem, Lisa Wasko DeVetter, associate professor of small fruits at Washington State University, said that clumping hives may also reduce pesticide exposure, and the practice promotes beekeeper efficiencies.

“Beekeepers were really keen to say, ‘It’s a lot easier for me, especially when I have a lot of contracts to fill, to clump those hives, place them away from the field edges and not deal as much with the dirt and mud and then go to the next farm as opposed to dispersing them strategically on the row ends of a field,’” she said.

The findings have emerged from a multiyear, multimillion dollar project, where researchers from several regions, including the Pacific Northwest, have been working to develop data-driven, evidence-based strategies for growers and beekeepers to improve blueberry pollination.

DeVetter noted that blueberry growers have long thought that placing hives at the ends of rows can help ensure adequate honeybee pollination. “But,” she said, “there was not data justifying this practice. So we asked the question, ‘What happens if you clump the hives and aggregate them away from the field edges?’”

Researchers in Washington, Oregon and Michigan spent two years comparing the effects of different hive placements in different fields and cultivars by measuring pollinator activity, pollinator outcomes, fruit set, berry size and seed set.

“I was really surprised by what we found,” DeVetter said. “We found that clumping has a positive effect on bee activity … and the clumped treatment had overall statistically more honeybee visiting those blueberry flowers relative to our dispersed treatment.”

“In fact, we calculated that clumping hives led to a 2.6 and 1.3 fold threshold increase in honeybees visitation in the Midwest and the Pacific Northwest, respectively,” she said.

Researchers were not able to document differences in fruit set, berry weight and seed set, DeVetter noted. “I think part of that is just the fact that we were working predominantly with Duke, and Duke is less pollen limited relative to other cultivars, like say, Liberty. So, it is possible that if we continue on asking this question with other cultivars, clumping might lead to increases in berry size, as well as seed set. But that remains to be discovered.”

When measuring pesticide residues on hives, researchers found a lot of variation, DeVetter said, but there was no statistical difference between detections on the clumped and dispersed hives. In a separate study in a field in Washington, DeVetter found that pesticide residues were lower on hives that were clumped than on hives dispersed at the ends of rows.

Researchers were measuring pesticide exposure on the outside of hives through use of silicone bands. “We weren’t doing assessments of pesticide residues inside the colony,” DeVetter said. “I think that is another important step of the research, to see what the colonies are getting actually exposed to with these different placement treatments.”

In conclusion, DeVetter said, “Clumping promotes beekeeper efficiencies and may reduce pesticide exposure without compromising pollination.”