We examined the correlation among different concentrations of Botran, DPX 965-75%, or DPX 965-50% (incorporated in artificial provision laden with spores of Aseosphaera aggregata Skou), the incidence of chalkbrood, and larval mortality of alfalfa leafcutting bee, Megaehile rotundata (F.). We noted a clear margin of safety between the high concentration that might kill larvae and low concentration needed to achieve substantial fungal control for Botran and DPX 965-75%; concentrations ranging from 0.5 to 5% reduced the >90% incidence of chalkbrood to <6% with little effect on larval health. When a concentration at 20% DPX 965-75% was added to provision, prepupal weight was significantly reduced. Prepupal weight also was reduced when Botran was added at ≿2:0.75%.