Urban heavy metal contamination limits bumble bee colony growth

1. Post-industrial shrinking cities contain abundant vacant land and are increasingly recognized for their pollinator conservation potential. At the same time, the industrial legacies of these urban ecosystems have resulted in elevated levels of heavy metals in surface soils, which could negatively affect bee populations.
2. We investigated whether foraging within heavy metal contaminated landscapes represents a fitness cost for the common Eastern bumble bee, Bombus impatiens, by placing colonies in residential backyards along an urban to rural gradient extending south and east from the city of Cleveland, Ohio, USA. Bees foraged in the landscape for three weeks, after which time we counted the total number of workers and larvae present in the colony and analyzed castes for the presence of heavy metals. We then assessed the relationship between landscape composition, heavy metal loads and caste abundance.
3. Colonies located in urban landscapes were more likely to be exposed to lead (Pb)...