Abstract :
[en] Bees depend entirely on floral resources for their nutrition. However, there is increasing evidence that bees also rely on floral resources, specifically on specialized metabolites (SM), to deal with endoparasites, either enhancing their tolerance (i.e., increasing fitness) or resistance (i.e., reducing parasite load). Thus, plant co-evolutions with not only herbivores but also pollinators have undeniably shaped SM profiles among their tissues. Although this topic has gained attention, research addressing bee-parasite-plant relationships remain scarce. To narrow this gap, we first determined the SM profiles in sunflower (SM: phenolamides) as well as cherry and heather (SM: flavonoids) tissues. Then, using microcolonies fed with control, natural or SM-enriched diets, we assessed how different pollen diets and their SM impacted the economically important bumblebee Bombus terrestris and its most prevalent gut parasite, the trypanosomatid Crithidia bombi. Finally, we tested whether infected bumblebees were able to self-medicate using choice bioassays. We found that SM were distributed unevenly among plant tissues with species-specific patterns. Besides, bumblebees were impacted differently according to the provided pollen diet but as expected, SM-enriched diets mostly had detrimental consequences (e.g., impeded colony development). We further found that SM could both boost and reduce parasite load. Finally, contrary to our expectations, infected bumblebees did not prefer therapeutic pollen diets when offered a choice. We discuss the limitations of our experiments in light of the criteria underlying self-medication. We argue that highly virulent parasites are more likely to trigger self-medicative behaviors and that designing a SM-free artificial diet as control is considerably needed.
