Effect of heather flavonoids on the buff-tailed bumblebee

Bees are subject to many environmental threats, one of which being parasites. Pollen and nectar from flowering plants contain secondary metabolites that are supplied to bees through their nutrition and can potentially influence the interaction with the parasite. In this master's thesis, the effects induced by the uptake of heather (Calluna vulgaris) pollen and its flavonoids in the buff-tailed bumblebee (Bombus terrestris) and its parasite (Crithidia bombi) effects were investigated. Using liquid chromatography and tandem mass spectrometry (HPLC-MS/MS), the specialized distribution of 22 flavonoids in heather was first demonstrated. The distribution of these toxins seems to favor the interaction with pollinators since pollen contains less flavonoids than leaves and nectar does not contain any flavonoids. On the contrary, both floral resources contain a terpenoid, probably the callunene, known to counteract C. bombi. In order to evaluate the influence of flavonoids on the bumblebee and its parasite effects, tests in parasitized and unparasitized bumblebee microcolonies were performed and bumblebees were subjected to different pollen diets; 'willow' (control), 'willow with flavonoid extract' (of leaf and of pollen) and 'heather'. The uptake of flavonoid extracts from leaves and pollen induced similar negative effects on the microcolonies by limiting offspring production and demonstrating their toxicity. The lower nutritional quality of heather pollen was demonstrated by comparing the 'willow' and 'heather' diets. The latter induces a reduction in the production of offspring, although this was lower than that observed with pure flavonoid extracts. Finally, parasitized microcolonies showed that the effect of the parasite at the microcolonial level was very weak compared to that of the diet. However, at the individual level, parasitic stress, like flavonoid stress, induced an increase in the immune response indicated by an increase in fat body mass. While no decrease in the parasite effect due to flavonoids was described, quite the opposite, heather pollen had a positive influence on this immune response which could be due to its terpenoid load which could not yet be tested.