Efficacy of the entomopathogenic fungi; Beauveria bassiana and Metarhizium anisopliae against the cowpea weevil, Callosobruchus maculatus F. (Coleoptera: Chrysomelidae: Bruchinae)

Abstract

Abstract The efficacy of the two entomopathogenic fungi, Metarhizium anisopliae (TR 106) and Beauveria bassiana (TR 217), was tested against the adults of the cowpea weevil, Callosobruchus maculatus F. (Coleoptera: Chrysomelidae: Bruchinae) in laboratory. Two concentrations of conidial suspensions (1 × 106 and 1 × 108 conidia/ml) of M. anisopliae and B. bassiana isolates were directly applied on four pairs of adult beetles in Petri dishes (2 ml/dish) and then incubated at two different climatic regimes; 22±1 °C and 26 ± 1 °C with 70 ± 5% RH, 16:8 h light-to-dark. Lethal time values (LT50 and LT90) were calculated using probit analysis. As a result, the LT50 and LT90 values of M. anisopliae (1 × 108 conidia/ml) were 4.45 and 5.34 days at 26 °C and 5.17 and 6.15 days at 22 °C, respectively. LT50 and LT90 values of B. bassiana (1 × 108 conidia/ml) were 4.07 and 5.11 days at 26 °C and 4.07 and 5.41 days at 22 °C, respectively. LT50 and LT90 values of M. anisopliae (1 × 106 conidia/ml) were 5.42 and 6.43 days at 26 °C and 6.08 and 7.54 days at 22 °C, respectively. The LT50 and LT90 values of B. bassiana (1 × 106 conidia/ml) were 5.67 and 7.15 days at 26 °C and 5.47 and 7.50 days at 22 °C, respectively. Approximately 100% of mycoses were obtained in all treatments. In general, the effectiveness of these two entomopathogens increased by increasing suspension concentrations and temperature. These results suggest that the two isolates may be very successful in biological control of the C. maculatus and may be alternatives for chemical pest management.

Keywords

• Callosobruchus maculatus
• Cowpea weevil
• Entomopathogenic fungi
• Virulence
• Temperature