Bacillus thuringiensis isolates from Egyptian soils and their potential activity against lepidopterous insects

This study aims to search for indigenous Bacillus thuringiensis (Bt) strains from the soils of different locations representing 11 Egyptian governorates. A total of 2671 colonies from 93 soil samples were examined. The total number of Bt positive soil samples was 40/93 i.e. 43.01%. The results indicate that the percentage of the occurrence of Bt in these samples was 3.818%. The Egyptian soil showed to be rich in Bt. The evaluation of the potential activity of 40 positive soil isolates against Spodoptera littoralis and Helicoverpa (=Heliothis) armigera was carried out. Subsequently, LC₅₀ and LC₉₀ values and the potency of the Bt isolates were determined when applied against the target insects with reference to three standard preparations.