Two isolates of the fungus Beauveria bassiana (Balsamo) Vuillemin, GHA and BF, were evaluated in Cape Verde in 1991 and 1992 for infectivity to the Senegalese grasshopper, Oedaleus senegalensis (Krauss), and the migratory locust, Locusta migratoria migratorioides (Reiche and Fairmaire). Evaluations included laboratory bioassays and small-scale field trials. Laboratory bioassays evaluated five different formulations. Four of the formulations tested showed strong dose–response patterns and significantly higher mortality than the untreated control or carriers minus spores. All four formulations achieved high mortality levels when applied at economically feasible dose rates. The GHA and BF isolates, formulated in an oil carrier with an emulsifier, were equally infectious to migratory locust nymphs. Six different formulations of GHA were evaluated in field trials. Field trials evaluated both direct effects (treatment of field plots infested with O. senegalensis) and indirect effects (treatment of plots without grasshoppers, after which grasshoppers were introduced). In both cases, all six formulations showed good biocontrol potential. Grasshoppers exposed to treated plots up to 72 h after application exhibited comparatively high mortality levels, indicating that large numbers of spores remained viable in the field for at least 3 days. This was confirmed by analysis of the viability of conidia from vegetation samples obtained in the field following treatment. In open-plot, small-scale field trials, two different formulations (oil and clay-based) of GHA resulted in high rates of infection and approximately 45% reductions in grasshopper densities in the treated plots 7 days after application, even though density-reduction results were "diluted" by grasshopper migration into and out of the test plots. Results of the Cape Verde evaluations demonstrate that biopesticides developed from B. bassiana represent a promising alternative to chemical pesticides for grasshopper and locust control.