Development of a test design for a semi-field, colony-feeding study for the common eastern bumble bee (Hymenoptera: Apidae)

Ecological risk assessment is a key component of the regulatory process required for registration of crop protection products around the world. The western honey bee (Apis mellifera) is the model organism for pesticide risk assessments for bees, but there are uncertainties over whether it is predictive of risks to other bees. Consequently, efforts are underway to develop test methodologies for other non-Apis bees. We conducted a semi-field colony-feeding study with Bombus impatiens colonies to develop a colony-level methodology for bumble bees. We exposed commercially available bumble bee colonies to diets consisting of 4 concentration treatments of dimethoate insecticide (0.05, 0.19, 0.75, and 3.0 mg a.i./L) via supplemental sugar solution for 6 wk and compared exposed colonies to untreated controls. Each treatment group had 10 replicate colonies, with 1 replicate per treatment group represented at each of the 10 study rural locations. We collected data on various colony-level endpoints including production of female reproductive (gyne) offspring, colony weight, foraging activity, and consumption of provisioned sugar solution. Our results indicated that the test design could be used to derive concentration-response relationships for several endpoints including the most sensitive, colony mass (No Observed Adverse Effect Concentration = 0.05 mg a.i./L). Overall, our study provides the foundation for a semi-field, colony-feeding study test design for bumble bees, thus adding to the growing body of studies that may be used to assess the protectiveness of the honey bee risk assessment framework for non-Apis bees exposed to pesticides.