Susceptibility of Sitophilus zeamais (Motsch.) (Coleoptera : Curculionidae) and Prostephanus truncatus (Horn) (Coleoptera : Bostrichidae) to entomopathogenic fungi from Ethiopia

The efficacy of 13 isolates of entomopathogenic fungi belonging to Beauveria, Metarhizium or Paecilomyces spp. was assessed against Sitophilus zeamais (Coleoptera: Curculionidae) and Prostephanus truncatus (Coleoptera: Bostrichidae) using a total immersion bioassay technique in the laboratory. Fungi were applied at concentrations of 1 x 10(7) and 1 x 10(8) conidia mL(-1) for P truncatus and S. zeamais, respectively. All isolates tested were virulent to P truncatus (98-100% mortality, and median survival time (MST) ranged from 2.85-4.05 days). Metarhizium anisophae and B. bassiana were also virulent to S. zeamais (92-100% mortality, MST ranged from 3.58-6.28 days). The isolate of Paecilomyces sp.. was found to be the least virulent against S. zeamais, causing only 26.32 +/- 4.29% mortality with MST of 10.38 +/- 0.29 days. P truncatus proved more susceptible to the entomopathogenic fungi tested than S. zeamais. One M. anisophae (PPRC-EE) and three B. bassiana isolates (PPRC-HH, PPRC-9609 and PPRC-9614) were selected for further study and dose-mortality relationships were assessed on S. zeamais. The tested concentrations: ranged from 1 x 10(4)-1 x 10(7) conidia mL(-1). M. anisopliae (PPRC-EE) showed the lowest LC50 (3.39 x 10(5) conidia mL(-1)) followed by B. bassiana PPRC-HH (2.04 x 10(6) conidia mL(-1)). PPRC-9609 and PPRC-9614, showed slight differences in LC50 but not at LC90. The results revealed the higher potency of M. anisophae as compared with the B. bassiana isolates tested. The study suggests that the use of entomopathogenic fungi may hold promise as an alternative method to control pests of stored products in Ethiopia.