This work has been carried out in order to construct a potent Bt strain active against the Egyptian cotton leaf worm S. littoralis. This work has been carried out in order to construct a potent Bt strain active against the Egyptian cotton leaf worm S. littoralis. In bioassays, cry1Ac-expressing kur-HD73 and cry1Ag-expressing Bt4 Bt strains caused mortality of S. littoralis larvae only slightly. When Cry1C and Cry1Ag were applied together, an additive effect was obtained. In the presence of only Cry1C, the LC50 was 70 ppm. In the presence of Cry1Ac, the LC50 was 240 ppm, and it was 120 ppm in...