【目的】 苜蓿切叶蜂Megachile rotundata是全球应用最广的传粉昆虫之一，为明确其筑巢规律和影响筑巢活动的主要气象因子，并评估其在现有巢室释放密度下对苜蓿种子的增产效应。【方法】 采用巢板和纸吸管两种诱蜂法，观测了授粉期内雌蜂筑巢量的动态变化情况，并通过样方测产和单位面积种子产量分级法，评价了蜂房外东北40°、东南130°、西南220°和西北310°在0-140 m内的增产效果。【结果】 6月初放蜂后1-2周内筑巢活动缓慢，中旬到达高峰期后持续约2周，6月底以后筑巢活动逐渐减缓，雌蜂更喜好在东或东南方位的巢板上筑巢，在东90°-西260°范围内，筑巢量与方位角极显著负相关（P＜0.001）。通过筑巢量与7个常见气象指标的相关性分析发现，平均温度、最高温度、昼长与筑巢量显著正相关（P＜0.05），是影响雌蜂筑巢活动的关键气象因子。此外，在单个蜂房释放3-4万巢室的现有密度下，成虫羽化率为61%，有效授粉范围为40 m（约0.50 hm²），较自然授粉增产1.94-3.58倍，蜂群密度为3.60-4.80万头/hm²，主要朝西南方位扩散。【结论】 东-东南方位是诱集雌蜂筑巢最佳的巢板悬挂方位，平均温度24 ℃、最高温度32 ℃、昼长>14.86 h可作为筛选扩繁地的参考环境信息，且现有巢室释放密度的授粉效力仍不足，需增加蜂群投入满足制种需求。

 [Aim]  The alfalfa leafcutting bee (Megachile rotundata) is one of the most widely used managed pollinators worldwide. This study aimed to clarify the nesting habits of female bees and identify the key meteorological factors affecting their nesting activity, and evaluate the efficacy of M. rotundata in increasing alfalfa seed yield under the current cell release density. [Methods]  Two bee-trapping methods (nesting boards and paper straws) were used to monitor the dynamic changes in the number of sealed holes constructed by female bees during the pollination period. The impact on seed yield was assessed within the range of 0-140 m in four directions outside the bee domicile (northeast 40°, southeast 130°, southwest 220°, and northwest 310°) using the quadrat yield measurement method and the classification method of seed yield per unit area. [Results]  Our results indicated that the nesting activity was slow in the first 2 weeks after bee release in early June, peaked in mid-June and remained at a high level for approximately two weeks, then gradually declined after late June. Female bees showed a clear preference for nesting boards oriented toward the east or southeast. Within the azimuth range of 90° east to 260° west, the number of sealed holes exhibited a highly significant negative correlation with azimuth angle (P < 0.001). Correlation analysis between the number of sealed holes and seven common meteorological variables indicated that mean temperature, maximum temperature and daylength were significantly positively correlated with the number of sealed holes (P < 0.05), identifying them as key meteorological factors affecting the nesting activity of female bees. Additionally, under the current release density of 30 000-40 000 cells per bee domicile, the adult emergence rate was 61%, the effective pollination range was within 40 m of the bee domicile (covering approximately 0.50 hm²), resulting in a 1.94-3.58-fold increase in alfalfa seed yield compared with natural pollination. The corresponding effective bee density was 36 000-48 000 bees per hectare, with dispersal mainly toward the southwest. [Conclusion]  Our findings suggested that the east-southeast direction is optimal for hanging nesting boards to attract female M. rotundata. Environmental conditions including a mean temperature of 24 ℃, a maximum temperature of 32 ℃ and a daylength longer than 14.86 h can serve as reference indices for selecting brood-production sites. Moreover, pollination efficiency under the current cell release density remains insufficient, and increasing bee input is required to meet the demands of alfalfa seed production.