Evaluation of the Pathogenicity of Beauveria bassiana Biopesticide against Blattella germanica (Blattaria: Ectobiidae)

Behzad  Nourozi; Shahyad  Azari-Hamidian; Farzad  Majidi-Shilsar; Mohammad  Noori Sepehr; Mohammad  Naimi-Joubani

doi:10.18502/jad.v19i4.21213

Behzad Nourozi Research Center of Health and Environment, School of Health, Guilan University of Medical Sciences, Rasht, Iran
Shahyad Azari-Hamidian Research Center of Health and Environment, School of Health, Guilan University of Medical Sciences, Rasht, Iran
Farzad Majidi-Shilsar Department of Plant Protection, Rice Research Institute, Rasht, Iran
Mohammad Noori Sepehr Research Center for Health, Safety and Environment, Department of Environmental Health, School of Health, Alborz University of Medical Sciences, Karaj, Iran
Mohammad Naimi-Joubani Research Center of Health and Environment, School of Health, Guilan University of Medical Sciences, Rasht, Iran

DOI: https://doi.org/10.18502/jad.v19i4.21213

Keywords: Entomopathogenic fungi; Biological control; Integrated pest management; German cockroach

Abstract

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