Technical Abstract: The alfalfa leafcutting bee, Megachile rotundata F. (Hymenoptera: Megachilidae), is an important pollinator for the commercial production of alfalfa seed. However, poor nest establishment is an ongoing problem for bee managers. Megachile rotundata are solitary, yet gregarious bees that nest in pre-existing cavities. When selecting nest cavities, M. rotundata are attracted to previously used nests. Nests consist of a linear series of cells, each containing several components that may serve as cues for nesting females. In the current study, we sought to: a) determine if there is a preference for cells that previously held male or female conspecific bees, b) verify attraction to conspecific whole nest cells, and c) determine which individual nest components of a cell are attractive to nesting females. In a series of cage and open field experiments, M. rotundata females were allowed to initiate nests in blocks containing whole cells or individual cell components from old nests. Their nest choices were compared using ANOVA and REGWQ. Females were attracted to whole cells from old nests in both cage and open field studies. They were equally attracted to male and female cells. Also, they were equally attracted to whole cells from conspecifics and from another megachilid bee, Osmia lignaria. In cages, they were equally attracted to all cell components. However, in the open field, females preferred some cell components over others. These results provide a foundation for future studies to identify potential chemical lures to aid in the retention of bee populations at commercial nest sites.