Megachile rotundata (F.), a gregarious, cavity-nesting, leaf-cutting bee, is used throughout North America for the pollination of alfalfa, Medicago sativa L., seed crops. We examined the influence of various temperature regimes on development, survival, emergence, and longevity in both nondiapausing and diapausing forms of this species. In general, development rates increased with increasing constant temperatures used in this study (18, 22, 26, and 29°C), but the 26 and 29°C treatments were clearly superior as rearing temperatures for immatures. In diapausing individuals, a variable temperature treatment 14:27°C (8:16 h daily cycle, mean 22°C) reduced the length of prepupal and pupal development stages following incubation in the early summer when compared with individuals reared under the constant 22°C treatment. We discuss the importance of differing temperature regimes on M. rotundata development, survival, and longevity over the entire life cycle. We also discuss the importance of making a connection between immature development and sufficient wintering conditions to postdiapause development, a topic that has received much more attention in the literature.