OCCURRENCE OF CHALKBROOD CAUSED BY <i>ASCOSPHAERA AGGREGATA</i> SKOU IN A NATIVE LEAFCUTTING BEE, <i>MEGACHILE RELATIVA</i> CRESSON (HYMENOPTERA: MEGACHILIDAE), IN SASKATCHEWAN

Abstract

The alfalfa leafcutting bee, Megachile rotundata (Fab.), is an important domesticated pollinator of alfalfa grown for seed in Canada. Chalkbrood, a disease caused by the fungus Ascosphaera aggregata Skou, has caused high mortalities in M. rotundata populations in the northwestern United States since 1972. Chalkbrood was found in Manitoba in 1982, Alberta in 1983, and Saskatchewan in 1984 (Richards 1985). Although subsequent surveys have indicated the presence of A. aggregata at high levels in some southern Alberta M. rotundata populations, the disease has been detected only sporadically and at low levels in Saskatchewan populations (Goerzen 1990).