Ecologists studying tritrophic interactions have established that plant secondary chemistry can be detrimental to herbivores, but in some contexts can also provide resistance to natural enemies and pathogens.
We hypothesized that secondary compounds in nectar might similarly help pollinators resist pathogen infection. We initially found broad support for this hypothesis in an experiment testing eight nectar secondary chemicals in separate experiments using the Crithidia gut pathogen in Bombus impatiens (Richardson et al 2015). However, follow-up experiments by former graduate student Evan Palmer-Young suggested a more nuanced relationship, in which nectar secondary chemicals reduce Crithidia in some contexts but not others (e.g., Palmer-Young et al 2017, PLoS One), possibly because Crithidia strains vary in their resistance to secondary chemicals (Palmer-Young et al 2016, Scientific Reports), Crithidia evolves resistance quickly to secondary chemicals, even in mixtures (Palmer-Young et al 2016, Journal of Evolutionary Biology). In general, the concentration of secondary chemicals needed to suppress Crithidia growth in cell culture is orders of magnitude higher than concentrations that have sometimes been effective in bees (Palmer-Young et al 2016, Scientific Reports), suggesting that mechanisms of diet-mediated resistance are mediated by the host immune system or gut microbiome.
More recently, postdoctoral researcher Gordon Fitch and graduate student Seanne Clemente are studying the role of floral volatiles from the mint family (the native perennial wild bergamot, and agricultural crop basil) to reduce Crithidia infection, the potential for self-medicating behavior in infected bees, and consequences for pollination services and selection on chemical phenotypes.
