Overwintering alfalfa leafcutting bee cells, Megachile rotundata, were sampled from northwestern states and Canada. Cells were x-radiographed and scored. Cells containing healthy prepupae were incubated in the laboratory, and the subsequent daily emergence of adults was recorded by sex. Cells from which no adult emerged were dissected to determine stage of bee mortality and sex of dead pupae or adults. Bee populations that had been incubated in commercial settings also were evaluated to determine adult emergence success. There were statistical differences between the bee populations from the U.S. and Canada in adult survival and sex ratios, but not in emergence onset and duration. Also fewer bees survived in the commercial setting than in controlled conditions of the laboratory. Significantly more bees survived the incubation process if they were from a Canadian source, and if they were incubated under laboratory conditions. There was no difference in the likelihood of bee survival during incubation according to sex, but prepupal mortality was higher than pupal or adult mortality.