Preventative medicine? Examining prophylactic effects of a sunflower pollen diet in Bombus impatiens

The widespread decline of pollinator populations is of concern for both
natural and agricultural ecosystems. Pathogens have been identified as a
major contributor to the decline of some bee species, making understanding
host-pathogen dynamics a crucial area of research. Sunflower pollen
(Helianthus annuus) dramatically and consistently reduces infection by a
prevalent gut pathogen, Crithidia bombi, in the common eastern bumble bee
(Bombus impatiens), when consumed by bees post-infection, but we do not
know if sunflower can confer protection when consumed before exposure. We
asked whether feeding bumble bees sunflower pollen diets before pathogen
exposure decreases Crithidia infection compared to buckwheat pollen
(Fagopyrum esculentum). Buckwheat pollen was used as a comparison since it
has a similar protein concentration as sunflower pollen, but results in
high Crithidia counts when consumed post-infection. Bumble bees were fed
sunflower or buckwheat pollen for seven days, inoculated with Crithidia,
and then fed a wildflower pollen control diet for seven more days before
assessing infection. We found that consuming a sunflower pollen diet
before inoculation did not reduce Crithidia cell counts compared to
buckwheat pollen. Further, bumble bee survival and consumption of sucrose
solution and pollen did not differ between these diets. The results show
no evidence of sunflower pollen providing prophylactic resistance against
Crithidia bombi infection, indicating that the timing at which sunflower
pollen is consumed relative to exposure has important consequences for
infection.