COS 117-6 - Effect of sunflowers on bumble bee pathogen infection and colony reproduction

Background/Question/Methods

Food resources can alter host-pathogen dynamics not only via nutrition, but in some cases via chemical or mechanical traits that reduce infection. Many pollinator species are declining due to a range of factors including parasites and pathogens, but the potential for specific plant species to structure pollinator-pathogen interactions is largely unrecognized. Our previous work discovered that consuming sunflower pollen (Helianthus annuus) dramatically and consistently reduced infection by the gut pathogen Crithidia bombi in the common eastern bumble bee, Bombus impatiens. We then assessed whether these laboratory results could impact colony-level infection and reproduction by placing B. impatiens colonies at 20 farms with varying abundances of sunflower, and measuring infection intensity and daughter queen production over the season. In addition, we evaluated whether sunflower pollen also reduced C. bombi infection in the laboratory using three other wild bumble bee species: B. bimaculatus, B. grisecollis, and B. vagans.

Results/Conclusions

Sunflower abundance on farms reduced infection prevalence and intensity for C. bombi but not other pathogens, including Apicystis and Black Queen Cell virus. By contrast, general floral resource abundance and diversity did not explain significant variation in C. bombi infection. Furthermore, bee colonies on farms with more sunflowers produced more daughter queens, suggesting that reduced infection translated to colony-level reproductive benefits. In the laboratory, we found that sunflower pollen had relatively weak effects in reducing C. bombi infection in B. vagans and B. bimaculatus, and no effect in B. grisecollis. These surprising results indicate that the mechanism by which sunflower reduces C. bombi infection is specific to certain bumble bee species. Future comparative work and collaboration with a molecular biologist will help us elucidate the mechanism by which sunflower could so effectively reduce infection in one bumble bee species but not another. Because B. impatiens is not in decline but other bee species are less stable, planting sunflowers might benefit a species already doing well. On the other hand, because B. impatiens is dominant it may drive pathogen dynamics in other bee species. Future work will consider whether planting sunflowers will ultimately benefit pollinator communities.