국내 토양으로부터 파밤나방에 활성있는 Bacillus thuringiensis subsp. kurstaki KB100균주를 분리 동정하였다. 난방제 해충인 파밤나방에 대한 B. thuringiensis의 살충력을 강화시키기 위해 몇 개의 protease inhibitor를 조사하였으며, 이 중 단백질 분해 억제 능력이 가장 좋은 tannic acid을 선발하였다. B. thuringiensis의 배양액에 tannic acid을 혼합 처리하여 파밤나방 2령 유충을 대상으로 생물활성을 조사한 결과, B. thuringiensis 단독처리는 54.4%의 사충율을 보인 반면 B. thuringiensis와 4 mM tannic acid을 혼합하여 처리하면 64.0% 그리고 B. thuringiensis+40 mM tannic acid는 95.5%의 높은 상승효과를 각각 나타냈다. 그러나 B. thuringiensis+80 mM tannic acid 에서는 53.3%로 단독처리의 경우 보다 사충율이 낮게 나타났다. 3령 유충에서도 B. thuringiensis 단독처리는 60.0%였으며 B. thuringiensis+40 mM tannic acid는 93.3%로 사충율이 증가하는 상승효과를 보였다. 야외포장 실험에서 B. thuringiensis 단독처리는 1회, 2회, 3회 누적 처리에서 각각 61.8%, 80.4% 그리고 47.3%의 사충율을 나타낸 것에 비해 B. thuringiensis와 40 mM tannic acid의 혼합 처리구에서는 83.9%, 89.4%와 66.8%로 사충율이 증가되었다.
Bacillus thuringiensis subsp. kurstaki KB100 isolated from the domestic soil have the most effective activity against the beet armyworm, Spodoptera exigua larva. The tannic acid as protease inhibitor might be increased the efficacy of sublethal concentrations of B. thuringiensis. The tannic acid was identified as a protease inhibitor that could increased the efficacy of sublethal concentrations of B. thuringiensis. Mixture of B. thuringiensis and tannic acid was investigated the mortality of S. exigua larva in the laboratory and field. When B. thuringiensis treated to 2nd larva of S. exigua, mortality was shown 54.4%. However, mixtures of B. thuringiensis with 4 and 40 mM tannic acid were increased mortalities to 2nd larva of S. exigua as 64.0 and 95.5%, respectively. Also, synergy effect of mixture of B. thuringiensis and 40 mM tannic acid was increased the mortality of S. exigua 3rd larva to 93.3%, even though 60.0% mortality with only B. thuringiensis treatment. On the other hand, the mortality of mixture with B. thuringiensis and 80 mM tannic acid was 53.3% lower than B. thuringiensis single treatment. In the welsh onion field, the accumulated mortalities of 3 times replicated with mixture of B. thuringiensis and 40 mM tannic acid were 83.9, 89.4 and 66.8% compare with 61.8, 80.4 and 47.3% as only B. thuringiensis treatment, respectively.
