Entomopathogenic fungi with approximately 1000 known species are key regulatory factors in insect pest population. Also, these agents infect insects by direct penetration of the cuticle and thus provide the only practical means of microbial control of insects that feed on plant or animal juices as well as for the many coleopterans and orthopteran pest which have very few known viral or bacterial diseases. Beauveria bassiana is a widespread entomopathogenic fungi that infect many insect species. The aim of the current study was to determine the effect of different composition of oil in pathogenicity of the fungus. So, the fungus was grown on Potato dextrose agar (PDA) at 25 degrees C. Conidia were harvested from 14-day sporulating cultures by scraping the surface with a spatula and suspending the conidia in sterile 0.03% aqueous Tween 80.Two controls were done one was different concentrations of spore without oil and the other only oil. The insects were collected from the wheat farm in and maintained on wheat plants in the laboratory at 27+/-2 degrees C under a 14 h light: 10 h dark (LD 14:10) photoperiod. Assays were done with dipping methods. The results showed that there are significant differences in mortality of insects in two spore emulsions, one oil formulated and the other spores in sterile water without oil usage. Oil formulation enhances fungal virulence toward insect. Since insect cuticle especially epicuticle (lipid layer) is the primary site of establishment of mycosis, oil formulation increase the adhesion of spore to the insect cuticle through hydrophobic interaction between the spore and cuticle surface.