Abstract/Summary

In recent years, pollinator risk assessments (PRAs) were developed to address the risk from pesticide exposure to pollinators. Pollen and nectar can be contaminated with a range of pesticides, such as insecticides, fungicides, and herbicides. Since these matrices are important food sources for pollinators and other beneficial insects, contaminated pollen and nectar can represent a key route of exposure. However, limited knowledge exists about residue levels and dynamics in these matrices for many crops and active ingredients (AIs). Consequently, extensive field trials are required to obtain reliable residue values for PRAs, which involve immense expenditure and many resources. The first aim of this thesis was to improve the understanding of factors that influence residue levels in pollinator-important matrices and identify the processes governing residue dynamics in pollen and nectar. The second aim was to investigate correlations and relationships between residues in pollen and nectar and other plant matrices, in order to provide insights towards the facilitation of PRAs. Glasshouse studies were established with the plant species Cucurbita pepo L and Helianthus annuus L, due to their abundant production of pollen and nectar and suitability to be grown under controlled conditions. This study focussed on a systemic (cyprodinil) and a contact (fludioxonil) fungicide as model AIs to investigate residue dynamics in various floral matrices following a foliar spray application. Significant differences in residue levels and dynamics were found between both crops, AIs, and floral matrices. Residues found in H. annuus were overall higher than residues found in various C. pepo matrices, which could be attributed to the lower biomass of H. annuus and reduced growth dilution after application. Leaves and flowers generally exhibited the highest residues in both species and nectar the lowest residues. Significant variations in residue levels observed in pollen and anthers indicated that complex translocation pathways influenced the residue levels and dynamics, which were determined by translaminar movement and translocation of both AIs. Residues in pollen were particularly influenced by many factors, such as the lipophilicity of the compound and pollen type, the temperature, and the application rate. In contrast, residues in nectar were less affected by these factors and remained at a low level close to the limit of quantification. Furthermore, it was demonstrated that relationships in residue levels between floral matrices exist and simple models achieved acceptable accuracy for residue estimation in pollen, which could justify the use of surrogate matrices in PRAs. In order to achieve more precise estimations, particularly for mainly translocation-dominated processes, more elaborate models are required which can quantify the contribution of the above-mentioned parameters to the residue dynamics during anthesis.