The studiesk aimed (i) to determine LC₅₀ and LT₅₀ values of Bacillus thuringiensis var. aizawai strain against fall armyworm larvae, (ii) to assess the efficacy of Bacillus thuringiensis var. aizawai strain against fall armyworm larvae in the laboratory conditions.

The results showed that in the laboratory conditions, after 7 days of inoculation, at concentration of 10³ CFU.ml^-1 of Bacillus thuringiensis var. aizawai strain against the first instar larvae of the fall armyworm presented that the efficacy achieved upper 50 percent; at concentration of 10⁴ CFU.ml^-1 presented that the efficacy achieved upper 50 percent on the second instar larvae; at concentration of 10⁵ CFU.ml^-1 presented that the efficacy achieved upper 50 percent on the third instar larvae; at concentration of 10⁷ CFU.ml^-1 presented that the efficacy achieved upper 50 percent on the fourth instar larvae. The LC₅₀ values of Bacillus thuringiensis var. aizawai strain on 1^st, 2^nd, 3^rd and 4^th instar larvae were 3,36 × 10⁴; 7,24 × 10⁵; 1,09 × 10⁶ and 5,70 × 10⁶ CFU.ml^-1, respectively. The LT₅₀ values of Bacillus thuringiensis var. aizawai strain on larvae instars of fall armyworm were 32,568 hours (at concentration of 10⁸ CFU.ml^-1 on 1^st larvae); 114,864 hours (at concentration of 10⁷ CFU.ml^-1 on 2^nd larvae); 126,432 hours (at concentration of 10⁷ CFU.ml^-1 on 3^rd larvae) and 153,432 hours (at concentration of 10⁸ CFU.m^-1 on 4^th larvae). Besides that, the Bacillus thuringiensis var. aizawai  also bring hight effective on eggs, the mortality ranged 95.15 to 100% at 10⁸ to 10⁹ CFU.ml^-1  at 5 days after hatching.