Efficacy of Ethiopian Beauveria bassiana and Metarhiziumanisopliae isolates on spotted spider mites, Tetranychusurticae (Acari: tetranychidae) under laboratory conditions

Abstract

The efficacy of six Beauveria bassiana and nine Metarhiziumanisopliae isolates of Ethiopian origin were bioassayed in the laboratory replicated 4 times for their lethal effects against the adult of Tetranychusurticae with the aim to incorporate as bio- agent component for IPM of the two spider mites. All the tested isolates were pathogenic tothe two spotted spider mite at 1x10⁸ conidia ml- concentration, but virulence ranged from 45.4% to 90.0% with LT₅₀ from 3.19 to 11.81 days. Based on the extent of mortality, isolates PPRC 29, PPRC 27, PPRC 19, PPRC 66, and EE of Metarhizium; and GG and HH of Beauveria were moderately virulent (60-80%) and PPRC 2 &PPRC 61 of Metarhizium; and9615 & 9604 of Beauveria are weak (<60%). Four isolates (MM &PPRC 6 of Metarhizium; and 9614&9609 of Beauveria) which caused mortality ranges of 86% to 90%,were categorized as highly virulent and further evaluated at four different doses (1×10⁵, 1×10⁶, 1×10⁷ and 1×10⁸ ml^-1). The isolates inoculated at different concentrations significantly differed in their efficacy and the higher concentration (1×10⁸ conidia ml^-1) caused higher mortality than the lower (1×10⁵ conidia ml^-1). Isolate 9614 showed the least LC₅₀ (1.37×10⁵) followed by MM (1.9×10⁵). Therefore the two isolates, B. bassiana 9614 and M.anisopliae MM, which caused higher mortalities within shorter periods, were promising bioagents for the management of the two spotted spider mites.