Spiny pollens from different species in the sunflower family reduce parasite infection in the common eastern bumble bee (Bombus impatiens)

Laura L Figueroa, Alison Fowler, Stephanie Lopez, Victoria E Amaral, Hauke Koch, Philip C Stevenson, Rebecca E Irwin, Lynn S Adler

This is a plain language summary of a Functional Ecology research article which can be found here.

The importance of bees as pollinators is now widely acknowledged and we are increasingly aware of the numerous stressors that can negatively impact pollinator health. These include habitat loss, pesticide exposure, and parasites, all of which are linked to bee declines, especially in combination. An urgent question is what strategies we can implement to reduce the negative impacts of these stressors. Previous work has shown that sunflower pollen has a remarkably potent medicinal effect for the common eastern bumble bee (Bombus impatiens): bees that eat sunflower pollen have greatly decreased infection by a common gut parasite (Crithidia bombi). Infection with this parasite can reduce overwintering survival and negatively affect how bees forage for food from flowers. Sunflower pollen has a characteristically spiny outer shell but also contains a range of different chemicals which may contribute to the effect.

Bombus impatiens worker visiting a sunflower-family relative (credit Joel Brown)

Here we undertook experiments to compare the medicinal effects of sunflower and control pollen before and after extracting the chemicals inside the pollen grains and found that it was the spiny outer shell of sunflower pollen, and not its chemistry, which reduced infections. Interestingly, other species in the sunflower family also have spiny pollen. Therefore, we also screened seven additional species from the sunflower family and found that four of them also strongly reduced infection by the gut parasite, suggesting that the effect may be widespread in the family. Given the results of our work, two key follow-up questions are: does having greater access to plants in the sunflower family in the field reduce infections in common eastern bumble bees? What are the effects for other bee species? By answering these questions, we can continue to expand our understanding of strategies that could promote pollinator health and bee conservation.

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