Project Overview

Reports

Commodities

Target Pests

Practices

Residual toxicity statements on pesticide labels are informed by tests, whereby treated foliage is harvested at specified intervals of weathering to determine whether honey bee contact with this foliage results in mortality. The information is of considerable importance to both beekeepers and pesticide applicators to determine whether toxic products sprayed at dusk would dissipate by the following morning. Residual toxicity is estimated by the Environmental Protection Agency (EPA) in terms of RT25 or the duration it takes honey bee mortality after exposure to aged product residues to decline below 25% of test bees. Although RT25 values are prominent on pesticide labels, used widely by pesticide applicators and featured prominently in state Managed Pollinator Protection plans (MP3) EPA has expressed concerns around the variability of these estimates. It is also unclear how estimates developed for honey bees relate to other bee taxa. Finally, it is unknown whether RT25 estimates align with standard language provided to registrants by EPA. We propose to analyze the sources of variability in RT25 from over 1,200 residual toxicity assays published in the literature, constituting over 130 pesticide active ingredients. Analysis will focus on variability in lab conditions as well as in environmental conditions. Our analysis will generate RT25 estimates for these pesticides, as well as associate estimates of variability, not only for honey bees, but where data is available, for four other bee taxa. Finally, we propose to look at the alignment of these RT25 estimates with EPA published values and the residual toxicity statements on approximately 230 pesticide labels widely used around bloom in Oregon. The culmination of this work would be to revise the estimates of RT25 currently listed in the widely used and long-standing Extension publication How to Reduce Bee Poisoning from Pesticides (PNW-591), as well as slides outlining how to use residual toxicity in pesticide training. The work will help registrants and regulators understand the reliability of RT25 estimates as a predictor of how pesticides dissipate over the course of an evening, but will also help beekeepers and pesticide applicators recognize products with residual toxicity that are reliable. Finally, the project will provide feedback to EPA and state pesticide regulators on labels that inaccurately convey residual toxicity to pesticide applicators.    

The overarching goals of this project are to: 1) characterize the variability of residual toxicity under different lab and field conditions and for different bee taxa and 2) to determine how this variability is reflected on insecticides labels used during full bloom in Oregon.  We will achieve these goals though three objectives:

1. Explore variation in RT25 estimates from published studies. 
   1. Estimate RT25 values and levels of uncertainty in these values for the most widely used insecticides at bloom.
   2. Determine the sources of variability arising from differences in lab and field conditions under which assay were performed.
   3. Compare estimates across bee taxa to resolve whether RT25 values are transferable from honey bees to other bees. 
2. Alignment of RT25 values with information provided to pesticide applicators. 
   1. Compare RT25 estimates from objective 1 to estimates published by EPA.
   2. Characterize the alignment between RT25 values from objective 1 and from EPA relative to residual toxicity statements on pesticide labels. 
3. Incorporate RT25 values into pesticide safety education training and into Extension material that are used across Western states.