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.

Key words/phrases: Entomopathogenic fungi, Metarhizium, Mexican bean bruchid, Mycosis, Pathogenicity, Zabrotes subfasciatus.