Evaluation on the Potential of Entomopathogenic Fungal Isolates for the Control of Mexican Bean Bruchid (Zabrotes Subfasciatus) (Coleoptera: Bruchidae

Abstract

The efficacy of five isolates of entomopathogenic fungi belonging to the genus Metarhizium was assessed against Mexican bean bruchid, Zabrotes subfasciatus (Boheman) (Coleoptera: Bruchidae) in a laboratory experiment. Four local isolates namely META-B, META-D, PPRC-6, PPRC-29 and one standard isolate ICIPE-30 were evaluated. Pathogenicity of the isolates was conducted with three different conidia concentrations including 106, 107 and 108 conidia/ml. The adults of Mexican bean bruchid were treated by spraying one ml of fungal concentrations ranging from 1x106 to 1x108. All the isolates tested were virulent at all concentrations ranging from 1x106 to 1x108 conidia/ml. However, pathogenicity (based on speed and magnitude of mortality) varied among isolates and concentration. Among the M. anisopliae isolates, ICIPE-30 and META-D were most pathogenic. A significant difference (p<0.05) in mortality was recorded between treatments of fungal concentrations and the control. None of the control treatment units gave more than 15% mortality. All tested isolates were able to infect and cause mycosis in adult Mexican bean bruchid, out of which isolate META-B showed the least virulence compared to others with less than 67.5% mortality with confirmed symptom of mycosis. The study suggests that entomopathogenic fungi may be used as a component of IPM in stored beans under Ethiopian conditions