Background: Fungal pathogens of Hypera postica (Gyllenhall) (Coleoptera: Curculionidae) were collected from the vicinities of Adana and Igdir in Turkey. The pathogenicity of the fungal isolates against the pest were investigated. According to morphologic (colony morphology, spore shape) and molecular (sequences of ITS1-5.8S ITS2 region and EF1-a, Bloc, and RPB1 genes) characterizations, the isolates were identified as Beauveria bassiana (HpI-2, HpI-6, HpI-7, HpI-10, HpA-3, HpA-4, HpA-5) and Beauveria pseudobassiana (HpI-4). All these strains were isolated from H. postica for the first time. In order to determine pathogenesis of all isolates on the target pest, bioassays were conducted against larvae and adults, as screening of (1 x 10(7) conidia/ml) and dose-response (1 x 10(5), 1x10(6), 1 x 10(7), 1x10(8), conidia/ml), under laboratory conditions. The fungal isolates, closely related to each other, yielded significantly varied mortalities on larvae and adults. H. postica larvae were found more susceptible than adults to the fungal isolates in all tests. The highest mortality rates (100 and 98%) for larvae and adults, respectively, were obtained by B. bassiana strain HpA-5 within 14 days at 1 x 10(8) conidia/ml concentration. The median lethal concentration (LD50) of HpA-5 required to kill the larvae and adults of H. postica at concentrations of 2.37 x 10(4) and 1.4 x 10(5) conidia/ml, respectively. These results are promising; therefore, the B. bassiana strain HpA-5 can potentially be used against H. postica.