Exposure to chromium alters urban bumble bee behavior

Urban bees foraging in contaminated landscapes are exposed to heavy metals that result from a history of construction and demolition, manufacturing and industrial activities, and dense transportation networks. While field realistic metal concentrations do not cause bumble bee forager mortality, sublethal metal concentrations may influence foraging ability. For instance, sublethal exposure to certain metals are known to challenge honey bee memory and recall abilities, and impact bee feeding time on flowers grown in metal contaminated soil. We examined how field realistic concentrations of chromium (Cr), a common urban metal, influence bumble bee forager behavior using RFID tracking systems. We predict that bumble bees exposed to chromium will perform fewer but longer foraging bouts due to challenged navigation and recall. Using paired RFID readers, we designed four units to measure the directionality, forage trip duration, and return colony ID for bumble bees marked with RFID tags. Test bees (n=78) from four naïve Bombus impatiens colonies were tagged with unique RFID tags and returned to their natal colonies. Two colonies were randomly assigned to treatment and fed a sucrose solution with 0.25 ppm Cr and two control colonies were fed uncontaminated sucrose solution for three days, and all colonies foraged in field for 14 days. While there was no difference in the number of bees that left each colony, bees exposed to Cr were more likely to enter a non-natal colony at least one time compared to control bees. Preliminary results suggest that sublethal exposure to Cr may impact behavior or navigation.