Variation of insect mortality speed among B. bassiana isolates also reported by Kassa et al., (2002) who stated that different B. bassiana isolate had a different deadly speed against Sitophilus zeamais (Motsch.) (Coleoptera: Curculionidae). For isolate PPRC-HH, mortality occured at the beginning of the second day and on the fourth day of the test insect mortality reached 100% so MST value (Median Survival Time) was shorter. Another isolates (PPRC-9609 and PPRC-9614), mortality of S. zeamais occured on the fourth day.