No matter how old or where it’s from, frozen sunflower pollen helps bumblebees fight off a common gut parasite that threatens bee health and pollination.

Bumblebees play a critical role as pollinators, but their populations are declining in many areas. One major threat is infection by parasites like Crithidia bombi, which can spread quickly and impair colony health. Recent research by Fowler and colleagues found that feeding bumblebees sunflower pollen dramatically reduces Crithidia infections. This promising discovery suggests sunflower pollen could be used as a supplement to control Crithidia in agricultural bumblebee colonies.

Crithidia bombi is a common gut parasite that infects many bumblebee species. It spreads when bees ingest parasite cells in contaminated pollen or faeces. Infection with Crithidia impairs colony health and queen survival and founding by attacking ovarian development. It can also reduce a bee’s learning ability, meaning that it struggles to identify nectar-rich flowers, exacerbating wider pollinator decline.

Bumblebees are critical agricultural pollinators, so effective management of this parasite is essential for food production. Even more so as it appears that commercial bumblebee hives are increasing infection in wild bees. Previous studies found sunflower pollen has potent medicinal effects against Crithidia, but it was unknown if stored pollen maintains this benefit over time.

How do you track a parasite?

Fowler and colleagues studied the Common Eastern Bumble Bee, Bombus impatiens (Apidae). It’s a common bumblebee in the eastern United States but also commercially produced for agriculture. The scientists purchased three colonies for tests, inoculated them with Crithidia and then isolated them.

The authors randomly assigned the bees to be fed either sunflower pollen or buckwheat pollen. The sunflower pollen was between one to five years old and came from either the USA or China. After seven days, the scientists examined the bees’ guts for Crithidia cells.

Sunflower pollen can reduce infection regardless of origin

The researchers found that the stored sunflower pollen, regardless of age or origin, significantly reduced Crithidia infections compared to a control pollen diet of buckwheat. The sunflower pollen was up to 5 years old and collected from different regions, yet maintained its potency against the parasite. Even the oldest pollen samples were not degraded and worked just as well at fighting Crithidia as the fresher pollen.

Freshness might not be critical to the sunflower pollen’s success, but rather its physical form. That means the medicinal effects persist over time when pollen is frozen. Given these results, the scientists propose sunflower pollen could be used as an effective supplement in commercial bumblebee colonies to reduce Crithidia infections and improve bee health. The ability to store the pollen for years without losing efficacy makes it more feasible to implement as a disease management tool.

Do greenhouses need the plant or the pollen?

If sunflower pollen is so good, there is one obvious question. Why do you need to fly it in from China? Why not grow it alongside the crops? A solution like that could work in some places and would benefit the wild bees, but as mentioned at the start, many bumblebees are not wild.

For companies that are using bumblebees commercially in greenhouses, growing sunflowers isn’t practical. Sunflowers take up space that could be used growing more crops. The second problem is that sunflowers take time and grow over a season.

Fowler and colleagues suggest sunflower pollen would work best as a bee dietary supplement. They don’t recommend giving the bees a pure sunflower pollen diet, as they note the pollen is low in protein and sodium. However, they say a 1:1 mix of sunflower pollen with wildflower pollen still gives bees the medicinal effect without damaging colony growth.

Fowler, A.E., Kola, E. and Adler, L.S. (2023) “The effect of sunflower pollen age and origin on pathogen infection in the common eastern bumble bee (Apidae: Hymenoptera),” Journal of Economic Entomology. Available at:

Cover: A bee crawling on a sunflower head. Image: Canva.

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