Pathogenicity of native strains of Bacillus thuringiensis, Beauveria bassiana and Metarhizium rileyi as entomopathogens against the polyphagous borer, Conogethes punctiferalis (Guenée) (Crambidae: Lepidoptera)

Abstract

Abstract Background The shoot and fruit borer, Conogethes punctiferalis (Guenée) (Crambidae: Lepidoptera), is a significant pest causing substantial economic losses across various crops. The need for alternative control methods has prompted the exploration of biological control using entomopathogenic fungi and bacteria. In this study, the pathogenicity of Beauveria bassiana , Metarhizium (Nomuraea) rileyi and Bacillus thuringiensis (Bt) against C. punctiferalis larvae and pupae was assessed through laboratory bioassays. Results Various concentrations of B. bassiana and M. rileyi spores, i.e. 1 × 102, 1 × 104, 1 × 106, 1 × 107 and 1 × 108 spores/ml, were tested alongside controls. Additionally, five strains of Bt (IIOR Bt-145, Bt-154, Bt-171, Bt-172 and Bt-127) were evaluated at concentrations of 0.5, 1.0, 1.5, 2.0 and 2.5 mg/ml. The LC50 values for B. bassiana and M. rileyi were 7.9 × 105 spores/ml and 8.7 × 104 spores/ml, respectively, after 4 and 6 days of post-treatment using the spray method. In the larval dip method, the LC50 values were 4.8 × 103 spores/ml for B. bassiana and 2.0 × 104 spores/ml for M. rileyi after 5 and 6 days of treatment, respectively. For pupae, the LC50 values were 1.2 × 106 spores/ml for B. bassiana and 4.3 × 104 spores/ml for M. rileyi after 4 and 7 days of treatment, respectively. Similarly, the five strains of Bt were effective against C. punctiferalis. However, Bt-154 demonstrated the highest efficacy, with LC50 values of 0.66 mg/ml in the spray method and 0.79 mg/ml in the larval dip method after 5 days of post-treatment. Conclusion The potential of entomopathogenic isolates as biocontrol agents against C. punctiferalis provided a promising alternative to synthetic insecticides in pest management. The efficacy of B. bassiana, M. rileyi and Bt strains suggests their suitability for integrated pest management strategies, potentially reducing reliance on chemical pesticides and minimizing the environmental impacts. Further field studies are warranted to validate the efficacy and practicality of these biocontrol agents in real-world agricultural settings.

Keywords

• Conogethes punctiferalis
• Entomopathogenic fungi
• Bacillus thuringiensis
• Biological control
• Larval dip method