Potential Risk of Residues From Neonicotinoid-Treated Sugar Beet 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. Environ Toxicol Chem 2023;42:1167-1177. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

High nutritional status promotes vitality of honey bees and mitigates negative effects of pesticides.

Honey bee health is affected by multiple stressors, such as the exposure to plant protection products (PPPs), dietary limitation, monofloral diets and pressure of diseases and pathogens and their interactions. Here, we analysed the interacting effects of plant protection products and low nutritional pollen source on honey bee health under semi-field conditions. We established a healthy honey bee colony in each of 24 tents, planted either with monofloral maize, maize with a diverse flower strip or with monofloral Phacelia tanacetifolia. To evaluate the interaction between exposure to PPPs and nutritional status, a mixture of the insecticide thiacloprid and the fungicide prochloraz was applied. For each colony, we investigated brood capping rate as well as adult longevity, body and head weight, and enzyme activity of acetylcholinesterase and P450 reductase of newly hatched worker bees. We found a significant reduced capping rate in treated maize compared to flowering strips and Phacelia, but no interaction effect between pesticide treatment and nutritional status on capping rate. The response to treatment on the longevity of adults differed significantly between maize and Phacelia, with flower strips being intermediate, indicating interaction effects of PPP treatment and low pollen quality in maize compared to Phacelia and flowering strip treatments. Head weight of newly hatched worker bees showed significant interaction of nutritional status and treatment of PPPs. PPPs slightly increased body weight in all nutritional statuses, except for Phacelia. Enzyme activity of acetylcholinesterase and P450 reductase showed significant different responses between maize and Phacelia to PPP exposure, but not between maize and flowering strip. Our results support the hypothesis that higher pollen quality promotes development of larvae and pupae, longevity of adults and detoxification of PPPs.

Pesticide residue survey of pollen loads collected by honeybees (Apis mellifera) in daily intervals at three agricultural sites in South Germany.

In agricultural landscapes honeybees and other pollinators are exposed to pesticides, often surveyed by residue analysis of bee bread. However, bee bread is a mixture of pollen pellets of different plants collected over a longer time period. Therefore, pesticide content in the hive varies with plant species and time of pollen collection. Hence, the analysis of bee bread is an approximate approach to gain information on detailed pesticide exposure during the agronomic active season. As high-resolution data is missing, we carried out a pesticide residue survey over five years (2012-2016) of daily collected pollen pellets at three agricultural distinct sites in southern Germany. 281 single day pollen samples were selected and subjected to a multi-pesticide residue analysis. Pesticide contaminations of pollen differed between the sites. Intensive pesticide exposure can be seen by high pesticide concentrations as well as a high amount of different pesticides detected. During the five years of observation 73 different pesticides were found, of which 84% are characterized as non-harmful to honeybees. To estimate pesticide risks for honeybees, the pollen hazard quotient (PHQ) was calculated. Even though pesticides were detected in sublethal concentrations, we found substances not supposed to be exposed to honey bees, indicating the necessity for further improvement of seed treatments and increasing awareness of flowering shrubs, field margins and pesticide drift. Additionally, an in-depth analysis of nine pollen samples, divided into sub-fractions dominated by single plant species, revealed even higher concentrations in single crops for some pesticides. We give precise residue data of 1,657 single pesticide detections, which should be used for realistic laboratory and field tests.