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The EPA's preliminary pollinator assessment for imidacloprid

The Environmental Protection Agency has conducted a preliminary pollinator assessment to support the registration review of imidacloprid, a widely used neonicotinoid insecticide. The EPA did not perform new experiments for this assessment, but instead conducted a review based on 75 studies from the open literature as well as data from a registrant-submitted database. This is one of four assessments of neonicotinoids that has been conducted, with clothianidin, thiamethoxam, and dinotefuran reviews coming out sometime in 2016.

This assessment evaluated the risk of imidacloprid to honey bees at both the individual and colony levels. It concludes that imidacloprid can pose risks to honey bee health, but these risks depend on the crop they are pollinating. The highest risk crops identified were cotton and citrus. Several other crops, such as tomatoes, small berries, corn, legumes, cucurbits, strawberries, pome fruits, stone fruits, tree nuts, and oilseeds were identified as posing a risk to individual bees, but the effects at the colony level were either minimal or unknown. The assessment further identified a threshold of imidacloprid; crops with nectar residues greater than 25 parts per billion caused harm to bees, but levels below this did not.

A major criticism of the study is that it excludes other bee species, despite the well-established evidence that other bees, such as bumble bees, differ in their sensitivity and exposure to pesticides. The EPA acknowledges in the report that there is uncertainty in extrapolating these findings to other bee species, but they continued to generalize the risk to all bees from these honey bee data.