Entomopathogenic fungi including Beauveria bassiana are potential control agents for Diuraphis noxia (Mordvilko), the Russian wheat aphid. In cage studies, inoculation of D. noxia adults with B. bassiana increased aphid mortality and decreased the overall rate of aphid population growth. However, the pathogen did not affect aphid fecundity significantly; when the mean number of nymphs produced daily per living adult was used as a criterion, fewer than 1% of the nymphs produced by Beauveria-treated adults showed signs of infection. The pathogen significantly reduced D. noxia populations on wheat and oat host plants in controlled environment studies, but not in field cages. Secondary spread of the pathogen from initially infected aphids apparently required high humidity levels and aphid movement in the immediate vicinity of sporulation, resulting in direct contact of healthy individuals with sporulating cadavers. Rapid growth rates of aphid populations in some treatments strongly mediated the effects of fungal epizootics, so that the size and duration of localized aphid congregations and colony growth rates can be expected to affect epizootic progress significantly. Formulation of B. bassiana into alginate granules with the osmoprotectant polyethylene glycol resulted in more rapid production of conidia, and may help protect the fungus from adverse environmental conditions in the field. Although plant canopy microenvironment conditions may be limiting to microbial control in dryland cereal production, possibilities exist for effective control where cereals are irrigated or are in more humid climates.