When methods matter: solvent effects on pollinator responses to quantum-dot-labeled pollen

BACKGROUND: Pollination, one of the key plant-animal interactions, has been intensively studied, yet a major gap remains in our ability to track the fate of individual pollen grains. Since 2019, the use of quantum dots (QDs) as an easy, cost-effective in situ pollen-labeling technique has begun to fill this gap by allowing direct, fine-scale tracking of pollen without impeding its transport. QDs are typically applied in a volatile organic solvent, a methodological step that is usually assumed to be behaviorally neutral, but could in principle alter floral visual and olfactory cues. Because accurate pollen tracking requires labeling methods that do not themselves affect pollinator behavior, we ask whether and how insect pollinators respond to flowers whose anthers have been treated with QDs and their solvent carrier. RESULTS: Using a common-garden experiment with genetically uniform Brassica napus plants, we compared pollinator visitation and foraging behavior among flowers bearing QDs-solvent treatments, solvent-only controls, and untreated controls. Overall, our results support the use of QDs as a powerful and generally acceptable tool for tracking pollen transfer: pollinators did not avoid flowers with QDs-labeled pollen. Visitation did not differ among flowers labeled with different QDs colors, supporting within-study comparisons of multiple QDs colors. However, we detected an effect of the solvent: flowers exposed to QDs-solvent and solvent-only treatments received fewer visits and, in some cases, reduced foraging activity, particularly in honeybees. CONCLUSIONS: Because accurate pollen tracking requires labeling methods that do not themselves affect pollinator behavior, our findings show that quantum dots meet this requirement. However, the solvent used for their application can influence pollinator behavior. These effects, although moderate, indicate that potential side effects of solvents and labeling procedures should be carefully considered, controlled, and reported when designing QDs-based experiments and interpreting pollinator behavior.