Systematic review of residual toxicity studies of pesticides to bees and comparison to language on pesticide labels using data from studies and the Environmental Protection Agency
Authors: Swanson Leah K. , Melathopoulos Andony , Bucy Matthew T. 
Published: June 2023

BACKGROUND

Residues of pesticides on crops can result in mortality to foraging bees. The likelihood of mortality can be mitigated by applying pesticides in the evening so that their residues dissipate by the following morning when bees resume foraging. The dissipation rates of different pesticides, or their residual toxicity, is captured in a public-facing database compiled by the U.S. Environmental Protection Agency (EPA), but the database includes only a fraction pesticides bees are likely to encounter in the environment. Pesticide applicators in the U.S. encounter a Pollinating Insect Hazard Statement on pesticide labels, which coarsely indicate which products dissipate over the course of an evening. There is reason to suspect that these statements may not align with residual toxicity data, given previous findings of significant misalignment from published data discovered on the acute toxicity section of the Pollinating Insect Hazard Statement. Without a complete database of residual toxicity estimates, however, it is not possible to determine whether the residual toxicity components of the Pollinating Insect Hazard Statement similarly diverge from published studies.

RESULTS

We compiled 48 studies and calculated the residual time to 25% mortality (RT25) of each assay for three different bee species (Apis mellifera, Nomia melanderi, andMegachile rotundata). Our findings were compared to the EPA published database of RT25values. Of the RT25values that we could compare, we found that over 90% of the values support a similar conclusion to EPA: that the active ingredient has extended residual toxicity (i.e., residues cause greater than 25% mortality for eight hours or more). Next, we compared our values and the EPA’s values to the Pollinating Insect Hazard Statement in the Environmental Hazards sections of 155 EPA registered product labels. Of these labels, a little less than a third (27%) presented their residual toxicity in a manner inconsistent with their calculated RT25and current EPA labeling guidelines. Moreover, over a third (33%) of labels contained an active ingredient which was neither listed under EPA’s RT25database nor had a published study to estimate this value.

CONCLUSION

Residual toxicity of pesticides is a key parameter used by pesticide applicators to reduce impacts of their applications to bees. We provide the first evidence that many pesticide labels may convey residual toxicity information to applicators that is not correct and could lead to bees being exposed to toxic residues on plants. We also show large gaps in the availability of contemporary residual toxicity study for many pesticides, suggesting either researchers should conduct studies to estimate RT25values for these products, or EPA should make data from registrants more readily available. Finally, our analysis identified significant variation found between RT25values among different bee species tested, and different formulations of the same active ingredient, suggesting these factors should be incorporated into future bee residual toxicity studies.