Characterization of “pollen balls” in commercial populations of the alfalfa leafcutting bee, Megachile rotundata in Canada

SummaryTo determine the quality of their leafcutting bees (Megachile rotundata), Canadian producers submit samples of loose cells to the Canadian Alfalfa Leafcutter Bee Cocoon Testing Centre (CCTC), Brooks, Alberta, for x-ray analysis. As part of the x-ray analysis report, the CCTC uses the category “pollen balls” to describe bee cells that have been provisioned with nectar and pollen, but in which the presence of larval development is not apparent. We determined the nature of this pollen ball category by comparing results obtained through x-ray analysis to those determined by visual examination of cut-open cells. A total of 35,241 cells were cut open and characterized as either: mouldy; broodless dry or wet provisions; collapsed egg; dead larvae (Instar 1, 2, 3 or 4); live prepupa; parasite; predator; or chalkbrood. Accuracy analysis indicated that the best agreement between the estimates of percent pollen balls obtained visually and using the x-ray method, occurred when wet and dry provision, collapsed ...