Abstract: Regulatory frameworks in North America and other regions are based on the honey bee, Apis mellifera L., as the model organism for Pollinator Risk Assessments. The suitability of the honey bee as a surrogate for other bee species has been questioned by stakeholders, but the lack of available methodology has been an obstacle to address this uncertainty. Bumble bees, Bombus spp., are important pollinators of various crops and there is emerging methodology for toxicity tests through multi-stakeholder efforts. We generated toxicity endpoints for the common eastern bumble bee (Bombus impatiens) to characterize toxicity of dimethoate, an insecticide and positive reference compound in bee testing. Our contact and oral dosing experiments showed that dimethoate is similar or less toxic to individual adult bumble bees when compared to honey bees. A bumble bee microcolony test with dimethoate via sugar solution identified a similar chronic exposure endpoint as observed for individuals (NOAEC of 0.1 ppm), largely driven by worker mortality rather than reproductive effects. We proceeded to a semi-field colony feeding study design to increase environmental relevance. Colonies were fed sugar solution containing four different concentrations of dimethoate, resulting in a colony level NOAEC of 0.19 ppm and a LOAEC of 0.75 ppm. Collectively, our results for bumble bees exposed to dimethoate indicate that 1) the honey bee Tier 1 screening based on individual bees tested under laboratory conditions is protective of bumble bees, and 2) there is little refinement from the individual bumble bee assessment to the colony level. Our toxicity model with B. impatiens provides support to the current honey bee-based regulatory risk assessment. Furthermore, these advancements in validation of existing and development of new methodology for B. impatiens can serve as a blueprint for pesticide testing with bumble bees.

Pamela Jensen Ph.D.

Principal Scientist, Bayer CropScience LP

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