evaluation of the pathogenicity of beauveria bassiana biopesticide against blattella germanica (blattaria: ectobiidae)

Background: the german cockroach, blattella germanica (blattaria: ectobiidae), is a worldwide urban pest. due to limitations of conventional insecticides, alternative controls are needed. entomopathogenic fungi-based biopesti­cides offer a promising solution. this study evaluated the pathogenicity of the indigenous beauveria bassiana rasht strain (mcb18) against the german cockroach.methods: a laboratory colony of b. germanica was maintained under controlled conditions. the toxicity of four spore concentrations (1.5×10², 1.5×10⁴, 1.5×10⁶, 1.5×10⁸ conidia/ml) of b. bassiana was evaluated against adult cockroaches using the direct immersion bioassay. daily mortality was recorded for 21 days using three replicates of 20 cockroaches each (n=60 per concentration). the lethal concentration (lc50 and lc90) values were estimated us­ing probit analysis.results: beauveria bassiana caused dose-dependent mortality. the highest cumulative mortality (100%) was ob­served at 1.5×10⁸ conidia/ml, while the lowest (15.79%) occurred at 1.5×10² conidia/ml. the lc50 and lc90 were estimated as 4.23×10³ conidia/ml and 1.59×10⁶ conidia/ml, respectively. the lt50 decreased with increasing concen­tration, reaching 8.475 days at 1.5×10⁸ conidia/ml. conidiation on cadavers increased with concentration but re­mained lower than mor­tality, indicating that death often occurred before external sporulation. one-way anova revealed significant differ­ences in mortality rates (f=74.942, df=(3, 8), p<0.001). post-hoc tukey's hsd test showed that the two highest concen­trations (1.5×10⁶ and 1.5×10⁸ conidia/ml) were not significantly different from each oth­er (p>0.05), although both caused significantly higher mortality than lower concentrations (p<0.001).conclusion: experimental findings confirmed b. bassiana as an effective entomopathogen against b. germanica, caus­ing significant mortality through cuticular penetration and internal proliferation.