D3161: Preventative medicine? Examining prophylactic effects of a sunflower pollen diet in bumble bees

Widespread decline of pollinator populations is of concern for both environmental conservation and agricultural practices. Pathogens have been identified as a major contributor to the decline of some bee populations, making understanding bee disease a crucial area of research. Sunflower pollen (Helianthus annuus) has been shown to dramatically reduce infection by a common gut parasite, Crithidia bombi, in the common eastern bumble bee (Bombus impatiens), when fed to bees post-infection, but we do not know if sunflower can confer protection when consumed before exposure. We asked whether feeding bumble bees a monofloral sunflower pollen diet prior to infection decreases Crithidia infection. Bumble bees were fed either sunflower or buckwheat pollen for 7 days, infected, and then fed a wildflower pollen control diet. Crithidia cells were counted 7 days after infection. Buckwheat was used as a comparison since it has similar protein content to sunflower but does not reduce Crithidia in a diet post-infection. We found that a sunflower pollen diet before infection did not reduce Crithidia cell count compared to the buckwheat pollen diet. Further, bumble bee survival and consumption of nectar and pollen did not differ between a sunflower or buckwheat diet provided before pathogen exposure. The results show no evidence of a prophylactic effect of sunflower pollen providing resistance against Crithidia bombi, indicating that the timing at which sunflower pollen is consumed relative to infection has important consequences for infection outcome.