Adults of Cassida vittata were treated in the laboratory with different concentrations of the fungal spores of Beauveria bassiana. The insects were dipped in the spore suspensions for five seconds. The concentrations used in the treatments were as follows, 10⁸, 5 x10⁷, 10⁷, 5 x10⁶ and 10⁶ spore/ml water.  The results show that the concentration of 10⁸ caused insect mortality of 5, 10, 20, 20, 35, 50, 70, and 90 % in the period from the second to the ninth day. A complete mortality was reached in the tenth day. The concentration of 5 x10⁷ caused 95 % mortality on the twelfth day. On the same day there were no differences between the two concentrations of 10⁷ and 5 x10⁶ in which the mortality was recorded as 85 %. The percent mortality was recorded as 80% when the insect were treated with the concentration of 10⁶ spore/ml. Insect treatment with the concentration of 10⁸ caused insect mortality of 5, 10, 20, 20, 35, 50, 70, and 90 % in the period from the second to the ninth day respectively. A complete mortality was reached in the tenth day. According to the field application with the concentration of 10⁸ spore/ml, the total numbers of adult at the beginning of the experiments were counted and recorded as 114 /25   and 107 / 25 plant in treated and control respectively. After two weeks it became 65/25 plant and 121 / 25 plants in treatment and control respectively. In the fourth week the number of insects was noticed to be decreased in both treatment and control and recorded 40 and 73 adult insect per 25 plants in treatment and control respectively. In the sixth week the insect population was gradually increased in both treatment and control in which the total number of adult was recorded as 69 and 198 / 25 plants in treatment and control respectively.