Potential Risk of Residues From Neonicotinoid-Treated Sugar Beet in Flowering Weeds to Honey Bees (Apis mellifera L.)

In 2018 the European Union (EU) banned the three neonicotinoid insecticides imidacloprid, clothianidin (CLO), and
thiamethoxam (TMX), but they can still be used if an EU Member State issues an emergency approval. Such an approval went
into effect in 2021 for TMX‐coated sugar beet seeds in Germany. Usually, this crop is harvested before flowering without
exposing non‐target organisms to the active ingredient or its metabolites. In addition to the approval, strict mitigation
measures were imposed by the EU and the German federal states. One of the measures was to monitor the drilling of sugar
beet and its impact on the environment. Hence we took residue samples from different bee and plant matrices and at
different dates to fully map beet growth in the German states of Lower Saxony, Bavaria, and Baden‐Württemberg. A total of
four treated and three untreated plots were surveyed, resulting in 189 samples. Residue data were evaluated using the US
Environmental Protection Agency BeeREX model to assess acute and chronic risk to honey bees from the samples, because
oral toxicity data are widely available for both TMX and CLO. Within treated plots, we found no residues either in pools of
nectar and honey crop samples (n = 24) or dead bee samples (n = 21). Although 13% of beebread and pollen samples and
88% of weed and sugar beet shoot samples were positive, the BeeREX model found no evidence of acute or chronic risk. We
also detected neonicotinoid residues in the nesting material of the solitary bee Osmia bicornis, probably from contaminated
soil of a treated plot. All control plots were free of residues. Currently, there are insufficient data on wild bee species to allow
for an individual risk assessment. In terms of the future use of these highly potent insecticides, therefore, it must be ensured
that all regulatory requirements are complied with to mitigate any unintentional exposure.