An understanding of the visiting behavior of the pollinator on a crop and the affecting factors on gene flow would help to predict the potential gene flow risk and develop the strategies to limit gene flow. In alfalfa (Medicago sativa L.), pollination requires a tripping mechanism by a pollinator to release the pollen. This typical pollination method implies that the variations in tripping efficiency among bee species may directly or indirectly affect alfalfa pollen dispersal and gene flow. The objective of this study was to quantify and compare the difference in the formation of alfalfa pollen cloud density resulting from the two distinct bee species, honeybees (Apis mellifera L.) and bumblebees (Bombus terrestris L.), and their indirect effects on the promotion of wind-blown pollen dispersal under turbulent or non-turbulent weather conditions. In this study, pollen collection using rotorod pollen collectors under caged or uncaged alfalfa plots indicated no alfalfa pollen released from the source in the absence of insects. In contrast, pollens detected within, and beyond the alfalfa pollen source evidenced the necessity of tripping the flowers by bees for pollen release. Bee species greatly affected the visiting duration of a single alfalfa flower and the number of tripped flowers min⁻¹. At the current experimental scale, although worker bees of bumblebees were less abundant than honeybees, they generated a significantly greater alfalfa pollen cloud density (mean across sampling times, dates, and weather conditions: 566 pollens m⁻³ h⁻¹) than that of honeybees (416 pollens m⁻³ h⁻¹), which was closely correlated with the higher number of tripped flowers by bumblebees (8.8 flowers min⁻¹) relative to honeybees (3.1 flowers min⁻¹). While the similar patterns of wind-blown alfalfa pollen density negatively correlated with the distance observed for the two bee species, the pollen density generated by bumblebees at the same distance from the pollen source was greater than the values by honeybees. Additionally, a directional wind effect was detected with the greater pollen density always observed at downwind sites. The developed model predicted that alfalfa pollen cloud density reached 95% reduction of maximum potential value at 31.6 m (10 pollens m⁻³ h⁻¹) from the source edge, providing the reference value to understand the wind-blown alfalfa pollen dispersal and create isolation distance. Thus, the results will be helpful to understand the factors affecting the visiting behavior of pollinating bees associated with the flowers tripping, predict the gene flow risk, and develop management strategies to mitigate gene flow in alfalfa.

了解传粉者对作物的访问行为和基因流动的影响因素将有助于预测潜在的基因流动风险并制定限制基因流动的策略。在紫花苜蓿（Medicago sativa L.）中，授粉需要传粉者的触发机制来释放花粉。这种典型的授粉方法意味着蜜蜂物种之间的触发效率的变化可能直接或间接地影响紫花苜蓿花粉的传播和基因流动。本研究的目的是量化和比较两种不同的蜜蜂物种蜜蜂 ( Apis mellifera L.) 和大黄蜂 ( Bombus terrestris ) 导致的苜蓿花粉云密度形成的差异。L.)，以及它们在湍流或非湍流天气条件下对促进风吹花粉传播的间接影响。在这项研究中，在笼子或未笼子的苜蓿地块下使用转子花粉收集器收集花粉表明，在没有昆虫的情况下，没有从源头释放出苜蓿花粉。相比之下，在紫花苜蓿花粉源内外检测到的花粉证明了蜜蜂为了释放花粉而绊倒花朵的必要性。蜜蜂种类对单株紫花苜蓿花的访问时间和绊花数 min ^{-1有很大影响}. 在目前的实验规模下，虽然大黄蜂的工蜂不如蜜蜂丰富，但它们产生的紫花苜蓿花粉云密度（采样时间、日期和天气条件的平均值：566 花粉 m ^-3 h ^-1）明显高于蜜蜂（416 花粉 m ^-3 h ^-1），这与大黄蜂（8.8 花 min ^-1）相对于蜜蜂（3.1 花 min ^-1）。虽然风吹苜蓿花粉密度的相似模式与观察到的两种蜜蜂的距离呈负相关，但距离花粉源相同距离的大黄蜂产生的花粉密度大于蜜蜂的值。此外，在顺风位置始终观察到较大的花粉密度，检测到定向风效应。所建立的模型预测紫花苜蓿花粉云密度在 31.6 m (10 花粉 m ^-3 h ^-1) 从源头边缘，为了解风吹紫花苜蓿花粉扩散和创造隔离距离提供参考价值。因此，该结果将有助于了解影响授粉蜜蜂访问行为的因素与花朵绊倒，预测基因流动风险，并制定管理策略以减轻苜蓿中的基因流动。