A review of available bumble bee colony end-points and identification of current knowledge gaps

Bumble bee adult chronic toxicity studies and bioassays to assess larval development in the laboratory are currently undergoing method validation and standardization through ring-testing. These test designs will contribute valuable data required for Tier 1 risk assessments for this significant and commercially valuable pollinator. While laboratory assays allow for a conservative, highly controlled, and standardized evaluation of the relationship between test item dose and organism response, they do not reflect field-realistic exposure scenarios and cannot adequately address potential impacts on whole colony development. Semi-field, landscape-level field, or feeding studies are more suitable to describe whole- colony health and development and potential impacts from pesticide exposure in an agricultural setting. However, evaluation end-points need to be clearly characterized and the associated assessment methodology should minimize variation across studies. This is especially true for field studies, where genetic and environmental variability will cause significant impacts on study results. Here, we seek to provide a comprehensive review of available bumble bee colony end-points, assess their relevance and suitability for higher tier studies examining field-realistic exposure scenarios, and identify data, method, and knowledge gaps that may guide future research activity.