Systematic review of residual toxicity studies of pesticides to bees and veracity of guidance on pesticide labels

Residues of pesticides on crops can result in mortality to foraging bees. Pesticide applicators in the U.S. encounter a 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. Without a complete database of residual toxicity estimates; however, it is not possible to determine whether the residual toxicity components of statements on pesticide labels similarly diverge from published studies. We compiled 50 studies on residual toxicity trials with formulated pesticides and calculated the residual time to 25% mortality (RT25) of each assay for three different bee species (Apis mellifera, Nomia melanderi, and Megachile rotundata). Our findings were compared to a U.S. Environmental Protection Agency (EPA) published database of RT25 values. Of the RT25 values that we could compare, we found that over 90% of the values support a similar conclusion to the EPA. Next, we compared our values and the EPA's values to the statements on 155 EPA registered pesticide product labels. Of these labels, a little less than a third presented their residual toxicity in a manner inconsistent with their calculated RT25 and current EPA labeling guidelines. Moreover, over a third of labels contained an active ingredient which was neither listed under the EPA's RT25 database nor had a published study to estimate this value. 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.