Technical Abstract: Samples of alfalfa leafcutting bees, Megachile rotundata, were collected at the end of the nesting season from commercial alfalfa fields in five northwestern states for a total of eight samples. Using x-radiographs, up to 100 cells with solid masses appearing to lack viable larvae were selected and dissected. The content of each dissected cell was determined (provision only, egg or first instar larva, pre- or post-defecating larva, moldy, or with pest), and the condition of any pollen-nectar provision was categorized as very dry, very wet, or moist. Cell content and condition as well as duration of nesting season was correlated with temperature and relative humidity collected using Hobo dataloggers placed with bee boards in nesting shelters. The results will afford a better understanding of why many alfalfa leafcutting bee cells fail to produce larvae, or why bees fail to lay eggs on provisions.