Research on alfalfa leafcutting bee, Megachile rotundata F.,populations in production period showed that a number of moulds in conjunction with bacteria,which are the major factors.The nest,leaf litter,pollen balls and nectar went moldy,and mold developed,which affect the bee larva feed and eggs hatched.In addition,chalkbrood that occurred by Ascosphaera aggregata affect the larva develops.The beekeepers of internal and external use the laminated wood boards in production period,and treat nest in hot and dip the cells in a bleach solution in following spring,prevent and control effect exceeded 90%.