Optimizing the spores persistence of two isolates of the entomopathogenic fungus, Beauveria bassiana, against ultraviolet radiation using nanocomposite formulation

The entomopathogenic fungus Beauveria bassiana is an important and universal biological control agent that is used to control many important pests such as cabbage aphid Brevicoryne brassicae. Main limitation of the use of this fungus is environmental persistence to initiate epidemics in susceptible host populations. In this research, the lethal effects of two isolates of the entomopathogenic fungus on adults and second instar nymphs of cabbage aphid and the stability of the entomopathogenic fungus and its nanocomposite formulation against UV-C radiation were investigated. The LC50 value of the cabbage aphid adults was equal to 2.5×105 in WE209 isolate and 9.8×104 spores/ml in WE277 isolate. The LC50 values in the second instar nymphs were 6.4×105 and 3.2×105 spores/ml, respectively. Spore germination after 2 and 3 h exposure to ultraviolet radiation equals to zero for both times in WE209 isolate and 6 and 32%, respectively in WE277 isolate. However, these values were 12% and 37% for WE209 and 65% and 38%, respectively for WE277 base on nanocomposite. These results showed that the nanocomposite of the entomopathogenic fungus B. bassiana based on montmorillonite/salep can be effectively used to increase the stability and as a result, increasing the virulence of the fungus.