Spore Load of Ascosphaera Species on Emerging Adults of the Alfalfa Leafcutting Bee, Megachile rotundata.

The spore load of Ascosphaera species spores on larval chalkbrood cadavers and newly emergent adults of the alfalfa leafcutting bee, Megachile rotundata, was determined. The spore content of chalkbrood cadavers ranged from 3 x 10 to 5 x 10. Adults emerging through zero to nine cadavers carried spores on all body parts examined by scanning electron microscopy. Estimates of the total number of spores obtained from a series of adult washes ranged from 9 x 10 to 8 x 10. Some adult males which emerged through no cadavers carried 10 to 10 spores, indicating that nesting materials might also have been contaminated. However, the control of chalkbrood in commercial bee populations may not be accomplished simply by providing clean nesting materials as adults may still emerge through diseased larvae.