Wild bumblebees infected by an intestinal parasite are drawn to turtlehead flowers, the nectar and pollen of which seem to offer a medicinal effect, according to findings to be published in Ecology. 

These intestinal parasites can affect bumblebee survival and reproduction, if left alone. However, recent work revealed that parasitized bumblebees self-medicate using nectar laced with nicotine, which reduced the number of parasites in the infected bees. But is it actually happening in the wild? 

To investigate, University of Vermont’s Leif Richardson and colleagues studied the effects a group of floral nectar compounds has on both bumblebee foraging and plant reproduction. Called iridoid glycosides, these chemicals are known as plant secondary metabolites – they might help with development but they’re not critical for survival. Iridoid glycosides are used to deter plant-eaters like deer, and they have the added benefit of reducing the parasite load of parasitized bees. The team focused on two iridoid glycoside compounds – aucubin and catalpol – in the nectar and pollen from four populations of a wetland plant called turtlehead. Bees help pollinate turtlehead throughout eastern North America. The team manipulated the concentrations of those chemicals in the flowers to investigate their effects on bee behavior. 

"We show that bees might be able to self-medicate, altering their foraging behavior when parasitized so as to maximize their consumption of beneficial plant secondary metabolite compounds,” study author Rebecca Irwin from North Carolina State University said in a statement. Compared to healthy bees, those that are infected with the intestinal parasite preferred visiting flowers with the highest iridoid glycoside concentrations. 

Furthermore, the team also found that nectar chemistry affects plant reproductive success too. Flowers with the highest concentrations of iridoid glycosides in their nectar contributed much more pollen to other flowers after visits from bees. “Secondary metabolites,” Richardson adds, “could influence plant reproduction via complex suites of interactions involving not only pollinators but also their natural enemies."

We also just learned that ants infected by fungal pathogens are known to self-medicate too.