Sunflower Pollen and Bumble Bee Health: Mechanisms, Modifiers and Trade‐Offs

Bumble bees face increasing pressure from interacting stressors, including pathogens, nutritional limitations, and agricultural intensification. Among natural dietary factors that modulate disease, Asteraceae pollen-particularly sunflower (<i>Helianthus annuus</i>)-has repeatedly been shown to reduce infection by the trypanosomatid <i>Crithidia bombi</i> in bumble bees under laboratory conditions. Yet the mechanisms, generality, and ecological relevance of these effects remain incompletely resolved, and field-based evidence from European systems, particularly for <i>Bombus terrestris,</i> is scarce. Here, I synthesise current knowledge on how Asteraceae pollen traits influence <i>bumble bee</i> health, focusing on the interplay between pollen morphology, phenolamide chemistry, nutrient composition, gut microbiota, and host physiology. I evaluate evidence for three non-exclusive mechanistic pathways-mechanical abrasion, chemical activity, and microbiome-associated effects-and review emerging evidence for nutritional, immunological, and colony-level trade-offs associated with medicinal pollen. To place these mechanisms in a field-relevant context, I integrate pollen-trap data from <i>B. terrestris</i> and <i>Apis mellifera</i> colonies foraging in Central European agricultural landscapes, indicating strong seasonal reliance on Solanaceae pollen, no uptake of sunflower pollen by <i>B. terrestris,</i> and moderate use of <i>Silphium perfoliatum</i>, a perennial Asteraceae crop of growing agroecological interest. Together, these patterns highlight a mismatch between laboratory efficacy and field-level pollen use, indicating that sunflower pollen is unlikely to function as a standalone medicinal resource under realistic foraging conditions. Instead, potential health effects of Asteraceae pollen appear context dependent and embedded within diverse nutritional landscapes. I identify key knowledge gaps-including cultivar-level chemical variation, species-specific responses, and interactions with co-occurring stressors-and outline research priorities for evaluating when and how medicinal pollen may contribute to pollinator-supportive cropping systems.