The virulence of the mother and subcultures of Verticillium lecanii (Zimm.) Viegas maintained on an artificial medium (MYB) was determined. Each passage obtained from the artificial medium  was divided into two isolates, the first was left on the artificial medium to obtain the following passage, while the other was subsequently potentiated on a natural insect-host,the mealy bug Icerya seychellarum (Hemiptera: Monophlebidae). The LT₅₀ value on the mealy bug I. seychellarum exposed to a fungus concentration of 1.7×10⁸ spores/ml was calculated. The LT₅₀ value of the different subcultures (passages) on the natural host was as low as 4.6 days for the zero (mother) passage followed by 5.8, 7.4, 11.3,13.9 and 17.7 days for the five derived passages (subcultures on MYB ), respectively, while these values were low for those subcultures potentiated on I. seychellarum. The higher mortality percentage (100%) was obtained  after 13 days using the zero passage (mother culture) followed by 94.4, 79.8, 51.7, 44.9 and 36.0% mortality for 1^st, 2^nd,3^rd, 4th and 5^th subcultures (passages) maintained through the used artificial medium [MYB]), respectively. These results proved that the ascending number of passages of V. lecanii through the used artificial medium (MYB) loses its virulence against I. seychellarum. On the other hand, these results proved that potentiation of V. lecanii passages on a suitable insect-host (I. seychellarum) increase its virulence again and shorten the period of LT₅₀. Comparing the five passages potentiated on the natural insect-host (I. seychellarum) and those revealed that have been continuously maintained on the artificial medium, it was found that the virulence of the potentiated subcultures obtained from the natural insect-host was increased by 1.9 fold for the 5^th passage relative to the virulence of the same continuously obtained subculture from the artificial medium.