PHYSIOLOGY, BIOCHEMISTRY, AND TOXICOLOGY Postcocooning Temperatures and Diapause in the Alfalfa Pollinator Megachile rotundata (Hymenoptera: Megachilidae)

Megachile rotundata (F.), an adventive, gregarious, cavity-nesting, leaf cutting bee, is used throughout North America for the pollination of alfalfa, Medicago sativa L., seed crops. We examined the inßuence of various postcocooning (prewintering) temperature regimes on development, survival, emergence time, and longevity in both nondiapausing and diapausing forms of this species. Diapausing male and female M. rotundata required 27Ð30 d and 29Ð32 d, respectively, to develop from prepupae to emergence after incubation at constant 298C, regardless of postcocooning treatments to which they were exposed. Likewise, longevity after emergence was not related to postcocooning temperatures and ranged from5 to 6d and4 to 6d formales and females, respectively. Elevated postcocooning temperatures were associated with a higher prevalence of nondiapausing individuals, those completing development from eggs through emergence as adults in the same summer season. Relevance of our results to the commercial production of alfalfa leafcutting bees is discussed.