Submitted to: Bee Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 21, 1996
Publication Date: N/A
Interpretive Summary: The alfalfa leafcutting bee is used throughout northwestern North America for commercial alfalfa pollination. Chalkbrood is a fungus disease of bee larvae that can cause mortality in excess of 50% in managed bee populations. Beekeepers employ a variety of population management methods, some of which may exacerbate problems with bee disease. The purpose of this study was to estimate the number of fungus spores in the air within nest shelters and correlate spore levels with management practices and disease incidence. The results of aerial spore trapping showed that nest shelters with high levels of spores in the air early in the nesting season also had high disease levels later. Therefore, knowledge of the management history for bees within a shelter will allow prediction of disease incidence based on early-season spore trap counts. There was a clear difference among certain bee management methods in fungus spore counts and disease incidence. Disease levels increased, compared to the previous year, in shelters in which bees renested in used, contaminated nest materials. The management practice of forcing bees to move from contaminated nests in one season to clean nests in the next resulted in lower spore counts, but there was no significant change in disease incidence from the previous year. In a commercial management setting, use of trap counts could lead to management actions to minimize losses to disease.
Aerial traps were used to correlate estimates of the density of Ascosphaera aggregata spores with chalkbrood incidence in commercial nest shelters of the alfalfa leafcutting bee, Megachile rotundata. Spore counts and chalkbrood incidence were highest in populations renesting in the previous year's nest materials. Spore counts were low, but chalkbrood remained high, in populations that were 'phased-out' of old nest materials into new materials. The results show that trapped spore counts, combined with a knowledge of the management history of a population, can serve as a useful predictor of chalkbrood in commercially managed bee populations.