Toxicological assessment of Beauveria bassiana against Mexican bean beetle (Coleoptera:Coccinellidae)

Spore toxicity often Beauveria bassiana strains, grown on SDA medium at 27±2°C, and 80% RH, were evaluated against 3-day old larvae of Epilachna varivestis (Mulsant). Bioassays, using a dipped bean leaf assay, at ten doses between 1.23 and 1.27x10⁷ spores/ml were performed to evaluate toxicological activity. Treatments were incubated at 25±2°C, 60% RH, and 12:12. (L:D) per 72 h. All strains of B. bassiana showed toxicity to E. varivestis. A strain isolated from Diabrotica sp. showed the highest toxicity with 96.6% mortality, while isolates from Geraeus senilis, Diabrotica balteata, Hippodamia convergens, and Hypothenemus hampei resulted in mortalities of 93, 90, 90, and 86.6%, respectively; strains isolated from Curculionidae showed mortalities of 86.5 and 80%. The lowest mortality was observed for strains isolated from Sphenarium sp. at 76.6%, Oebalus mexicanus at 70%, and Cydia pomonella at 66%. The isolates from coleopterous insects showed higher toxicity than isolates from other orders. The time required for emergence of fungus from infected insects was 24 hours. Diabrotica sp., G. senilis, and D. balteata strains sporulated from over 90% of infected insects, while the strain from C. pomonella sporulated from only 67% of those infected.