Invasive plants as potential food resource for native pollinators: A case study with two invasive species and a generalist bumble bee

It is now well established that invasive plants may induce drifts in the quantity and/or quality of floral
resources. They are then often pointed out as a potential driver of bee decline. However, their impact on
bee population remains quite unclear and still controversial, as bee responses are highly variable among
species. Here, we compared the amino acid composition of pollen from three native and two invasive
plant species included in diets of common pollinators in NW Europe. Moreover, the nutritional intake
(i.e., pollen and amino acid intakes) of Bombus terrestris colonies and the pollen foraging behaviour
of workers (i.e., visiting rate, number of foraging trips, weight of pollen loads) were considered. We
found significant differences in pollen nutrients among the studied species according to the plant
invasive behaviour. We also found significant differences in pollen foraging behaviour according to the
plant species, from few to several foraging trips carrying small or large pollen loads. Such behavioural
differences directly impacted the pollen intake but depended more likely on plant morphology rather
than on plant invasive behaviour. These results suggest that common generalist bumble bees might
not always suffer from plant invasions, depending on their behavioural plasticity and nutritional
requirements.