Absence of pesticide avoidance during chronic colony-level exposure modifies locomotor activity in bumble bees

Exposure to pesticides partly depends on the foraging behavior of bees, which may exhibit indifference, deterrence, or attraction to contaminated food. In the present study, we conducted laboratory experiments to test the foraging avoidance of Bombus terrestris for honey syrup contaminated with field-realistic concentrations of the neonicotinoid acetamiprid (ACE), herbicide glyphosate (GLY), and fungicide metalaxyl-M (MET). Tests were also conducted with the recommended field concentration of a biopesticide, the sweet orange essential oil (EOE). Bees’ behavior, and lethal and sublethal effects of the pesticides on bumble bees were assessed at the individual (isolated foragers) and colony (colony exposure) levels. Bees did not display any avoidance for contaminated or uncontaminated food at the individual or colony levels in the ACE, GLY, and MET treatments. However, the EOE treatment reduced the consumption of honey syrup in relation to non-treated bees, resulting in lower survival of individual bees. At the individual level, no behavioral differences were observed between non-treated and treated bees. At the colony level, however, pesticide treatments modified bees’ walking behavior. In general, pesticides increased resting time and meandering, while reducing speed, movement, distance walked, and time spent moving fast. Our results demonstrate that bumble bees did not reduce food consumption of syrup contaminated with realistic concentrations of different common pesticides, resulting in detrimental effects on their behavior. Furthermore, bumble bees treated with the biopesticide field concentration reduced food consumption both at individual and colony levels. This treatment caused negative behavioral changes on bees and decreased the survival of isolated individuals.