The Oriental fruit fly, Bactrocera dorsalis (Diptera: Tephritidae) Hendel, has become the major pest of fruits in tropical Africa. The objective of the study was to evaluate the virulence of Ethiopian origin entomopathogenic fungal isolates of Beauveria bassiana (Balsamo-Crivelli) Vuillemin and Metarhizium anisopliae (Metchnikoff) Sorokin against the larva and pupa of the oriental fruit fly. Thirteen isolates (seven B. bassiana and six M. anisopliae) were bio-assayed in the laboratory. All the tested isolates were pathogenic to the larvae of B. dorsalis at 1x108 conidia ml-1 concentration with mortality range from 40.8% to 96%. Isolates S-39, 34-G and S-46 of Metarhizium and S-13 of Beauveria were categorized as highly virulent (81.7% to 96% mortality), isolate KF-3 and PPCR-29 of Metarhizium and S-39 of Beauveria moderately virulent (61.7%- 78% mortality), and isolates GF 3 of Metarhizium and 9609, 9604, S-46, S-10H and DLCO-41 of Beauveria weakly virulent (40.8-53.3% mortality). Dose-response assay was undertaken on the four highly virulent isolates at six different doses (1×104, 1×105, 1×106, 1×107, 1×108, and 1×109ml-1) on larvae of the fruit fly. The isolates varied in virulence and showed direct relationship between mortality and concentrations. Isolate S-39 showed the least LC50 (1.2×104) followed by GM-34 (1.6×104), S-46 (1.9x104) and S-13 (1.1x105). The bio-assay on pupae of the fruit fly showed that Metharizium isolates S-46 and S-39 caused about 50% pupal mortality at the highest concentration of 1x109, while the remaining two isolates, S-13 (Beauveria) and 34-GM (Metarhizium), caused below 50% pupal mortality at all concentrations. The four tested isolates are promising bio-agents against B. dorsalis and further field trials are recommended as a component of IPM program.
