29 Apr 2023

Pollination: better results also for out-of-soil crops

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Research in Washington shows how landscape can affect pollination of blueberries.

Every year, growers in blueberries are faced with deciding how many hives to stock their fields with to maximize pollination. The answer seems to lie beyond the edges of fields in the complex mosaic of the surrounding landscape. More than 75 percent of globally produced crops depend on insect pollination. Of these crops, many are pollinated by honey bees managed by placing rented hives in the fields during crop flowering.

The blueberry is one of the many crops that depend on insect-mediated pollination, but the issue of how many honey bee hives to place in a field to achieve optimal pollination is complex, and researchers and growers are looking for a solution to solve it.

QUESTIONS OF DENSITY

There have been many studies on honey bee densities in fields and other crops, but little research has been conducted on a larger landscape scale beyond field margins. Because the foraging radius of a honey bee is 1-2 km (0.6 to 1.2 miles) or sometimes more, field-level stocking rates may not take into account the contribution of other honey bees in the landscape that might contribute to pollination of blueberries.

Growers have also expressed concern that honey bees forage outside their fields, which sometimes causes them to increase stocking rates to ensure pollination in their fields. All this inspired the research team to look beyond the field edge to better understand pollination of blueberries.

A study has recently been completed that illuminates the role of the broader landscape context on blueberries pollination and yield. In an experiment conducted in northwest Washington on 16 fields of blueberries, results show that hive density in a 1,000-meter (0.6-mile) landscape best predicts honey bee visitation to flowers from blueberry in statistical models. In contrast, field-level hive densities poorly predict honey bee visits.

This suggests that field-level stocking density recommendations neglect the contribution of other hives in the landscape. In addition, it was found that as the percentage of blueberries in the landscape surrounding a field increases, the number of honey bee hives also increases.

Graph on the fields of blueberries for pollination.

Both results may seem simple and intuitive enough. But they have not been studied in pollination research. Revising honey bee density recommendations to consider the contribution of these insects in the broader landscape around a single field will require the collaboration of beekeepers, growers, and crop consultants, which may be difficult to achieve. However, if successful, the economic and ecological repercussions of overpopulation or underpopulation of fields can be avoided and optimal pollination can be achieved.

NOT ONLY HONEY BEES

In the Pacific Northwest, the presence of wild pollinating insects (bumblebees and solitary bees) are usually lower than the massive numbers of honeybees that growers introduce. However, wild pollinators can still contribute significantly to pollination, as they tend to be more efficient pollinators in plantations at blueberries. Therefore, it was also important to assess the effects of the landscape on wild pollinators.

It has been found that as the amount of semi-natural habitat around a field increases, more wild bees pollinate the plantations at blueberries. In contrast, honey bee visitation was not affected by more or less semi-natural habitat. Again, this is a simple and intuitive result, but it helps to draw a picture of the presence of pollinators in the landscape and informs pollination strategies.

Growers who want to increase wild pollinator populations should preserve or create habitats around their fields. Minimally disturbed hedgerows with flowering woody and herbaceous plants (e.g., willow and clover), as well as flowering strips, are examples of useful habitats for wild pollinators. Habitat creation will also be beneficial for honey bees by providing a more varied and nutritious diet from other floral resources.

This, in turn, can increase honey production, colony health, and pollination contribution throughout the year as they move to different crops.

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In combination with landscape-determined honey bee densities, appropriately populated farms should be able to strike a balance between crop pollination needs and grower budgets. This should also reduce competition for floral resources between wild pollinators and overabundant honey bees.

In conclusion, observing landscapes beyond field margins provides a more comprehensive understanding of crop pollination dynamics and will be useful in informing sustainable pollination strategies. The next steps will be to determine optimal colony density at the landscape scale to inform growers on how to restock their fields and prevent overpopulation.

Source: Growing Produce

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