D3124: The effect of sunflower pollen diet on bee parasite transmission

Parasites are a major driver of declines of both managed and wild bee populations. Thus, it is critical to understand ecological factors that can reduce disease transmission and increase bee health. Host diet can potentially structure disease outcomes, but surprisingly little research has assessed how diet affects parasite transmission. Numerous parasites afflict bumble bees, including Crithidia bombi, a fecal-orally transmitted trypanosomatid gut parasite that reduces learning, reproduction, and survival. Prior research has shown that a sunflower pollen diet reduces C. bombi infections in the common eastern bumble bee, Bombus impatiens. One mechanism driving this result is increased excretion; however, because C. bombi is fecal-orally transmitted, increased excretion could also increase parasite transmission. Alternatively, if sunflower pollen damages parasite cells, it may reduce infection and transmission. We conducted a series of experiments investigating how sunflower pollen affects C. bombi transmission in B. impatiens. To test if sunflower pollen affects the transmission potential of excreted C. bombi cells, we infected bees using a standardized number of parasite cells from the feces of either sunflower-fed or control-fed (buckwheat) infected bees and counted resulting parasite loads. We also counted parasite cells in infected sunflower-fed vs. control-fed bees. These results will be analyzed alongside excretion patterns in infected sunflower-fed vs. control-fed bees to understand transmission potential. Preliminary results show no difference in probability and intensity of infection with C. bombi cells excreted from sunflower-fed vs. control-fed bees when controlled for cell density. These results indicate that sunflower pollen does not stop parasite transmission.