Generalised host-plant feeding can hide sterol specialised foraging behaviours in bee-plant interactions

Host-plant selection is a key factor driving the ecology and evolution of insects. While the majority of phytophagous insects are highly host specific, generalist behaviour is quite widespread among bees and presumably involves physiological adaptations that remain largely unexplored. However floral visitation patterns suggest that generalist bees do not forage randomly on all available resources. While resource availability and accessibility as well as nectar composition have been widely explored, pollen chemistry could also have an impact on the range of suitable host-plants. This study focuses on particular pollen nutrients that cannot be synthesised de novo by insects but are key compounds of cell membranes and the precursor for moulting process: the sterols. We compared the sterol composition of pollen from the main host-plants of three generalist bees: Anthophora plumipes,Colletes cuniculariusand Osmia cornuta, as well as one specialist bee Andrena vaga. We also analysed the stero...