Abstract
Honey bees (Apis mellifera L.) are among the most important pollinators for agricultural and natural ecosystems, yet their health is increasingly jeopardized by multiple stressors, including pesticide exposure and declining food quality. Understanding how these factors interact is essential for improving ecotoxicological risk assessment and developing effective pollinator protection strategies. This dissertation addresses two underexplored aspects of honey bee ecotoxicology: the role of genetic diversity in shaping pesticide sensitivity and the combined influence of pollen contamination and nutritional traits on bee physiology and survival. The first part focused on acute oral toxicity, applying standardized OECD 213 assays to three insecticides with different modes of action, flupyradifurone (Si vanto® Prime), lambda-cyhalothrin (Karate Zeon®), and cyantraniliprole (Minecto™ One), across five honey bee genotypes (A. m. mellifera, A. m. carnica, A. m. ligustica, Buckfast, and a locally maintained population). Results revealed marked genotype-dependent variation in LD50 values, with certain genotypes showing greater tolerance depending on the compound tested. These findings demonstrate that genetic background is a critical determinant of pesticide sensitivity, a factor not yet accounted for in regulatory frameworks. The second part examined chronic oral toxicity (OECD 245) in the same genotypes and insecticides over a ten-day period. Chronic assays generally reflected the sensitivity patterns observed in acute tests but also uncovered toxicity dynamics not detectable in short-term exposures, including time-reinforced toxicity (TRT), fast-acting toxicity (FAT), and differences in feeding behavior. These results highlight the added value of chronic endpoints, which complement acute LD50 values and underscore the need to incorporate genotype diversity into pesticide evaluations. The third part investigated the role of pollen diets in mediating pesticide effects. A. m. ligustica bees were fed pollen from Malus domestica, Phacelia tanacetifolia, and Taraxacum officinale (orchard and alpine habitats), alongside a commercial supplement (Promotor-L Apis). Comprehensive analyses of residues, nutrients, and secondary metabolites revealed that pesticide contamination levels alone did not explain survival outcomes. Instead, other factors like pollen’s nutritional and phytochemical composition could have influenced the survival and physiological responses. Notably, uncontaminated alpine Taraxacum pollen caused high mortality and microbial disruption, whereas highly contaminated Malus pollen sup ported moderate survival and elevated vitellogenin. These findings demonstrate that bee health under chronic exposure is shaped not only by pesticide contamination, but more importantly by pollen quality and botanical origin. Taken together, the findings of this dissertation advance honey bee ecotoxicology by demonstrating that pesticide risk cannot be adequately evaluated through acute assays alone, by testing a single genotype, or by relying solely on residue measurements in pollen. Instead, genetic variation, exposure duration, and dietary quality act as decisive factors determining bee sensitivity and resilience. These insights provide a foundation for improving risk assessment frameworks so that they better reflect real-world exposure conditions.