(Montana State University - Bozeman, College of Agriculture, 2004) O'Neill, Ruth Pettinga; Chairperson, Graduate Committee: Sue Blodgett.
Nests from five seed alfalfa sites of the alfalfa leafcutting bee Megachile rotundata (F.) were monitored
over the duration of the nesting season in 2000 and 2001, from early July through late August. Cells
containing progeny of known age and known position within the nest were subsequently analyzed for
five commonly encountered categories of pre-diapause mortality in this species. Chalkbrood and pollen
ball had the strongest seasonal relationships of mortality factors studied. Chalkbrood incidence was
highest in early-produced cells. Pollen ball was higher in late-season cells. Chalkbrood, parasitism by
the chalcid Pteromalus venustus, and death of older larvae and prepupae , due to unknown source(s)
exhibited the strongest cell-position relationships. Both chalkbrood and parasitoid incidence were
highest in the inner portions of nests. The “unknown” category of mortality was highest in outer
portions of nests. Sex ratio was determined for a subset of progeny reared to adulthood. The ratio of
females to males is highest in cells in inner nest positions. Sex ratio is female-biased very early in the
nesting season, when all cells being provisioned are the inner cells of nests, due to the strong positional
effect on sex ratio.
