Bacillus thuringiensis with selected high toxicities against tobacco cutworm, Spodoptera litura were isolated from domestic soils. When being observed under a phase-contrast microscope, the insecticidal crystal proteins were showed a bipyramidal crystal types. New CAB 109 isolate was identified to B. thuringiensis subsp. aizawai in the H serotype. As a results of insecticidal activities between CAB 109 isolate and 3 existing ready-made products against 3rd larva of S. litura, CAB 109 isolate showed 100% mortality with spore concentration (1.3×10⁷ cfu/㎖). It was a very high insecticidal activity compared with a existing ready-made B. t. products. LD₅₀ values of CAB 109 isolate was 9.78×10⁵, 6.87×10⁶ and 1.83×10⁷ cfu/㎖ spore concentration against 2nd, 3rd and 4th larva of S. litura, respectively. Unlike Plutella xyfostella, S. litura was slowly died after application up to 7 days. The weight of S. litura larva applied with CAB 109 isolate were 6-7 times less than controlled group. Even though it didn"t die, it did not grow into next larva. The result observed with scanning electron microscope was that CAB 109 isolate of B. t. aizawai formed a typical bipyramidal crystal protein type. Otherwise, when CAB 109 isolate was examined with SDS-PAGE and with trypsin, there was no difference between CAB 109 strain and ready-made products of B. thuringiensis.

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