A semi-field colony feeding study using the common eastern bumble bee (Bombus impatiens)

A semi-field colony feeding study with the common eastern bumble bee (Bombus impatiens) was conducted in Vermont. Adapting recently developed semi-field study protocols for honey bee colony feeding studies, we exposed bumble bee colonies to four concentrations of dimethoate insecticide (0.05, 0.19, 0.75, and 3.00 ppm) delivered via sugar solution, and compared these colonies to controls. We established 10 sites around the margin of hayfields where pesticide usage was low and row crop agriculture accounted ~20% of land use in the range of bumble bee foragers. Each treatment group was represented by one colony at each site. Colonies were free to forage naturally, and were provisioned and inspected weekly over the course of the summer. We collected data on a range of individual- and colony-level endpoints relevant to bumble bee life history, including production of female reproductive (gyne) offspring, colony mass, foraging activity, and consumption of provisioned sugar solution. We found that dimethoate consumption exerted a concentration-dependent effect on these response variables, with the level of No Observed Adverse Effects Concentration (NOAEC) for most determined as 0.19 ppm dimethoate. Our work is novel in that it is the first fully-replicated semi-field colony feeding study to be conducted using B. impatiens, a key component of future risk assessment research for non-Apis bees in North America. We anticipate that our methods and results can guide future efforts to develop a standard test paradigm to assess risk of pesticides to bumble bees.