In recent years, the impact of Plant Protection Products (PPPs) on insect pollinator decline has 11 stimulated significant amounts of research, as well as political and public interest. PPP residues have 12 been found in various bee-related matrices, resulting in governmental bodies worldwide releasing 13 guidance documents on methods for the assessment of the overall risk of PPPs to different bee 14 species. An essential part of these risk assessments are PPP residues found in pollen and nectar, as 15 they represent a key route of exposure. However, PPP residue values in these matrices exhibit large 16 variations and are not available for many PPPs and crop species combinations, which results in 17 inaccurate estimations and uncertainties in risk evaluation. Additionally, residue studies on pollen and 18 nectar are expensive and practically challenging. An extrapolation between different cropping 19 scenarios and PPPs is not yet justified, as the behaviour of PPPs in pollen and nectar is poorly 20 understood. Therefore, this review aims to contribute to a better knowledge and understanding of 21 the fate of PPP residues in pollen and nectar and to outline knowledge gaps and future research needs. 22 The literature suggests that four primary factors, the crop type, the application method, the 23 physicochemical properties of a compound and the environmental conditions have the greatest 24 2 influence on PPP residues in pollen and nectar. However, these factors consist of many sub-factors 25 and initial effects may be disguised by different sampling methodologies, impeding their exact 26 characterisation. Moreover, knowledge about these factors is ambiguous and restricted to a few 27 compounds and plant species. We propose that future research should concentrate on identifying 28 relationships and common features amongst various PPP applications and crops, as well as an overall 29 quantification of the described parameters; in order to enable a reliable estimation of PPP residues in 30 pollen, nectar and other bee matrices.

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The ban imposed by the European Union on the use of neonicotinoids as sugar beet seed treatments was based on the exposure of bees to residues of neonicotinoids in pollen and nectar of succeeding crops. To address this concern, residues of thiamethoxam (TMX) and clothianidin (CTD) were analyzed in soil collected from fields planted in at least the previous year with thiamethoxam-treated sugar beet seed. This soil monitoring program was conducted at 94 sites across Germany in two separate years. In addition, a succeeding crop study assessed residues in soil, guttation fluid, pollen, and nectar sampled from untreated succeeding crops planted in the season after thiamethoxam seed-treated sugar beet at eight field sites across five countries. The overall mean residues observed in soil monitoring were 8.0 ± 0.5 µg TMX + CTD/kg in the season after the use of treated sugar beet seed. Residue values decreased with increasing time interval between the latest thiamethoxam or clothianidin application before sugar beet drilling and with lower application frequency. Residues were detected in guttation fluid (2.0-37.7 µg TMX/L); however, the risk to pollinators from this route of exposure is likely to be low, based on the reported levels of consumption. Residues of thiamethoxam and clothianidin in pollen and nectar sampled from the succeeding crops were detected at or below the limit of quantification (0.5-1 µg a.i./kg) in 86.7% of pollen and 98.6% of nectar samples and, unlike guttation fluid residues, were not correlated with measured soil residues. Residues in pollen and nectar are lower than reported sublethal adverse effect concentrations in studies with honeybee and bumble bee individuals and colonies fed only thiamethoxam-treated sucrose, and are lower than those reported to result in no effects in honeybees, bumble bees, and solitary bees foraging on seed-treated crops.