Bees are a key part of the production process for several food crops, including almonds and cherries, but just how much pollen do those crops produce? Researchers at Oregon State University have gained valuable insight into the pollen abundance and diversity available to honeybee colonies. They looked at five major pollinator-dependent crops in Oregon and California, including California’s almond industry.

A collaboration between Oregon State University and Texas A&M University, the study found that almond, cherry and meadowfoam provided ample pollen to honeybees, but highbush blueberry and hybrid carrot seed crops may not. As for that massive almond crop in California? Researchers found that it doesn’t provide as much pollen diversity as other crops, according to findings published recently in the Journal of Economic Entomology.

The western honeybee is a key pollinator of fruit, nut, vegetable and seed crops that depend on bee pollination for quality and yield. The study’s findings have value because both pollen abundance and diversity are critical for colony growth and survival of the honeybee, says Ramesh Sagili, the study corresponding author and an OSU associate professor of apiculture and honeybee Extension specialist.

Sagili explains that pollen diversity is important for the growth and development of bees, and low amounts of pollen to those colonies can affect brood rearing. “Beekeepers that employ their colonies for pollination of crops like hybrid carrot seed and highbush blueberry should frequently assess the amount of pollen stores in their colonies, and provide protein supplements if pollen stores are low,” he adds.

For honeybees, nectar and pollen are a key source of essential nutrients. A honeybee colony’s protein source is pollen, providing varying amounts of amino acids, lipids, vitamins and minerals. These nutrients obtained from pollen are essential for honeybee larvae development. Pollen largely contributes to the growth of fat bodies in larvae and egg development in the queen.

Taking on stressors

A well-nourished colony of honeybees is better able to withstand the impact of other stressors such as parasites and insecticides. And they’re more likely to survive the long-distance transport of colonies, which is known as “migratory management.” To pollinate crops around the country, bees are trucked where needed. For example, more than 1 million hives travel to California every year, just to pollinate almonds.

Less pollen diversity in the diet can hurt the colony’s defense system, which then can increase disease susceptibility and pesticide sensitivity. During critical crop bloom periods, growers rent large numbers of honeybees to pollinate their crops. About 2.5 million commercially managed honeybee colonies are used for crop pollination annually in the United States.

Some cropping systems may be putting bees at risk through temporary nutritional deficiency, if pollen is deficient in certain nutrients, and bees are unable to find an alternative source, according to Sagili.

He adds, “It’s crucial for beekeepers and crop producers to understand the pollen abundance and diversity that honeybees encounter during crop pollination.” He notes that blueberry and hybrid carrot seed producers can mitigate nutritional issues by offering supplemental food or forage, including commercially available protein supplements for bees.

Renting bee colonies to growers for pollination services is a significant business, but it also requires repeated transport of the colonies between crops throughout the growing season.

How the study worked

In this study, the research team collaborated with 17 migratory commercial beekeepers for pollen collection from honeybee colonies in five different cropping system in 2012, from late February to August. Researchers installed pollen traps on at least five colonies at each site and collected pollen from the colonies at the height of the blooming season.

They found that in California, where almonds are raised on more than 1 million acres, there’s more than enough pollen for the nearly 2 million honeybees at work in the crop to pollinate orchards. But they also found that pollen diversity was low compared to other crops.

“We think the reason for that is, almonds bloom early in the year, when there are so few plant species in bloom — so bees have few other forage options and primarily rely on almond pollen,” Sagili says. His observation comes from parts of the northern and southern ends of the San Joaquin Valley where no other crops are in bloom when almond trees bloom. This may contribute to poor availability of diverse pollen.

Study co-authors are Ellen Topitzhofer, Hannah Lucas, Priyadarshini Chakrabarti and Carolyn Breece, all researchers at OSU’s Honey Bee Lab; and Vaughn Bryant at Texas A&M’s Palynology Laboratory.

OSU Extension has several resources on honeybees and pollinator health. The Oregon State Beekeepers Association provided funding for the study.

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