Bacillus thuringiensis as biological agent has applied practically in pest control programs. However, the activity of this bacterium under field conditions and direct exposure of sun rays is decreased. In this study, persistence of Pathogenicity of this bacterium under field conditions and the role of protective agents includes active charcoal and starch for the first time in Iran was evaluated. Therefore, concentrations of bacteria alone and mixture with charcoal and starch in completely randomized block design experiment in three periods of time on 2nd instars larvae of Nyssia graecarius Staudinger were investigated and the protective effects of these materials in exposure of solar radiation until 9 days were evaluated. The bacteria insecticidal effect on larvae of N. graecarius was performed on basis this studies pathogenic effect of Bacillus thuringiensis after spraying on plants is decreasing significantly at less than 7 days and after 9 days its mortality was the same as control treatment. Percentage mortality of bacteria, bacteria mixed with activated charcoal, mixed with starch and control after 0, 7 and 9 day light exposure were (76.6, 70, 63.3, 6.6), (53.3, 63.6, 53.3, 10) and (30, 53.3, 40, 10), respectively. Results showed that persistence was increased when bacteria applied with active charcoal and starch and combination of Bacillus thuringiensis plus charcoal is more effective than mixture of Bacillus thuringiensis plus starch. The study showed that for increasing time and power bacteria control protective agents such as activated charcoal can be used.