The causes of variability in honey bee residual toxicity tests

Monday, November 14, 2022

9:24 AM – 9:36 AM PT

Location: Vancouver Convention Centre, Meeting Room 204

Presenting Author(s)

Leah Swanson

Student
Oregon State University
Corvallis, Oregon

Co-Author(s)

Andony Melathopoulos

Pollinator Health Extension Specialist
Oregon State University
Corvallis, Oregon

The residual toxicity (RT) of pesticides to bees on foliage is included on all pesticide labels under Environmental Hazards section. Estimates of RT are made from standardized assays where treated foliage is harvested at specified intervals of weathering to determine whether honey bee contact with this foliage results in mortality (EPA Ecological Guidance 850.3030). RT estimates are of considerable importance to beekeepers and pesticide applicators to determine whether toxic products sprayed at dusk would dissipate by the following morning. While all pesticide labels contain RT language, there is no comprehensive database of test results to evaluate labels. I completed a meta-analysis of 48 papers with 2729 individual RT trials of 59 insecticide active ingredients. I estimated residue time to 25% mortality (RT₂₅) values for each active ingredient and compared to the published values from United States Environmental Protection Agency and language found on pesticides labels corresponding to RT₂₅ values. I determined variation in methodologies did not influence estimates of RT₂₅ and estimates were consistent for pesticide active ingredients, regardless of formulation tested and the species of bee. Less than a third of RT warnings on 155 analyzed pesticide labels corresponded to calculated RT₂₅ values and a third failed to have any RT warning despite being toxic to bees. I was unable to compare RT₂₅values to almost 50% of pesticide labels due to a lack of overall RT data, indicating a need for additional RT testing of products to confirm label language.