Three entomopathogenic fungi, Beauveria bassiana (Bilsamo) Vuill. GHA, Metarhizium brunneum (Petch) F52, and Isaria javanica (Wise) strain 439 were evaluated for insecticidal activity against walnut husk maggot, Rhagoletis suavis (Loew), collected from husks of black walnut, Juglans nigra L., to identify the best pathogen for development of augmented biological control of the pest. The species of Rhagoletis from the field was confirmed to be sauvis by mitochondrial cytochrome c oxidase subunit I gene sequencing and by wing color patterns of adults. The larval stage of the walnut husk maggot was susceptible to each of the fungal pathogens. More field-collected maggots died from exposure to greater concentrations of fungal conidia. Probit analysis showed M. brunneum was 139 and 155 times more potent against maggots than were B. bassiana and I. javanica, respectively. Greater insecticidal activity of Metarhizium supports selection for further study as a biological control agent against Rhagoletis.