[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.