Landscape composition and local floral resources influence foraging behavior but not the size of Bombus impatiens Cresson (Hymenoptera: Apidae) workers

Here, we assessed how the morphology, weight and foraging behavior of
individual workers are affected by their surrounding landscape. We
hypothesized that colonies established in landscapes showing high cover of
intensive crops and low cover of flowering crops, as well as low amounts
of local floral resources, would produce smaller workers, which would
perform fewer foraging trips and collect pollen loads less constant in
species composition. We tested these predictions with 80 colonies of
commercially reared Bombus impatiens Cresson placed in 20 landscapes
spanning a gradient of agricultural intensification in southern Québec,
Canada. We estimated weekly rate at which workers entered and exited
colonies and captured eight workers per colony over a period of 14 weeks
during the spring and summer of 2016. Captured workers had their wing,
thorax, head, tibia, and dry weight measured, as well as their pollen load
extracted and identified to the lowest possible taxonomic level. We did
not detect any effect of landscape habitat composition on worker
morphology or body weight, but found that foraging activity decreased with
intensive crops. Moreover, higher diversity of local floral resources led
to lower pollen constancy in intensively cultivated landscapes. Finally,
we found a negative correlation between the size of workers and the
diversity of their pollen load. Our results provide additional evidence
that conservation actions regarding pollinators in arable landscapes
should be made at the landscape rather than at the farm level.