Technical Abstract: The alfalfa leafcutting bee, Megachile rotundata F. (Hymenoptera: Megachilidae) is widely used as a pollinator for production of alfalfa seed, and populations of these bees can be maintained by alfalfa seed growers or can be purchased from mostly Canadian bee providers. Megachile rotundata raised in Canada have higher survival rates during incubation after winter storage than bees produced in the northwestern U.S., but no reason has been found for this. We investigated whether storing immature M. rotundata for various time periods at a warm temperature (16ºC) before winter or allowing them to remain unmanaged at ambient temperatures affects physiological aspects of prepupae during the winter as well as the survival and longevity of adult bees after spring or summer incubation. Our results show that the timing of the onset of winter storage and incubation does affect prepupal weights, prepupal lipid and water contents, adult emergence, and adult female longevity. Winter storage of prepupae in November or December with a late June incubation time results in heavier adults that emerge more readily than bees incubated in May. However, adult females incubated in late May thrive longer than June-incubated bees if fed a honey-water diet. Thus, some prewinter management regimes for M. rotundata commercial stocks may be more effective than others in achieving optimal adult emergence synchrony, as well as adult survival and longevity for pollination of a summer crop.