Published online by Cambridge University Press: 31 May 2012
The alfalfa leafcutter bee, Megachile rotundata (F.), is the primary pollinator of commercially grown seed alfalfa in Canada. Chalkbrood is a fungal disease, caused by a complex of Ascosphaerales species (Skou and King 1984) that infect the larvae of many species of bees. One species, Ascosphaera aggregata Skou (Skou 1975), is a severe problem in leafcutter bees in the United States and in some cases has caused losses of more than 65% (Stephen et al. 1981). Mode of dispersal, infestation of bee larvae, sporulation, and associated symptomatology of this pathogen have been described (Vandenberg et al. 1980; Vandenberg and Stephen 1982; McManus and Youssef 1984).