The solitary bee Osmia lignaria Say has been developed as an orchard pollinator in the western United States. Immatures develop through the spring and summer. By late summer, bees
become adults and remain in this stage inside their cocoons throughout the winter. In this study, we reared O. lignaria at various temperature regimes in the laboratory and outdoors. Developmental rates increased with temperature: bees reared at 18°C took >120 d to complete development, whereas bees reared at 29°C took half that long. Bees reared outdoors under fluctuating ambient conditions took ?95 d. At 18°C, some bees were unable to complete prepupal dormancy. Different developmental stages responded differently to the various temperature regimes. Fluctuating temperatures averaging 22°C significantly shortened the dormant prepupal stage, and, as a result, bees developed faster than at the equivalent constant temperatures. Bees that developed faster (29°C and fluctuating temperatures) could be wintered as early as August and incubated for emergence in March, 1 mo ahead of bees exposed to natural conditions. These results can be applied to field populations for pollination of early-blooming crops such as almonds, Prunus amygdalus Batsch.