Isolation, identification, and toxicity of native Bacillus thuringiensis against Spodoptera litura

This study aimed at isolation and selection of Bacillus thuringiensis (Bt) with toxicity against Spodoptera litura in soil samples collected from southeastern region of Vietnam. Thirty nine Bt isolates were obtained from 32.63% of the 95 collected samples, resulting the total Bt index of 0.096. Light microscopy observation revealed the presence of variety morphology of parasporal crystals. Mortality rate of S. litura was maximum in the reference strain, B. thuringiensis var kurstaki (95%), followed by the two Bt isolates TN1 and TN2 (80% and 75%). The isolates showing the mortality rate of 20% to 40% and below 20% constituted, respectively, 38.46% and 34.62%of the assessed isolates. PCR analysis method was used with the universal primers to detect the presence of cry1 and cry2 type genes. Ten isolates showed the presence of the expected amplicons and 90% of the Bt isolates contained cry1 genes. Four Bt isolates harbored both cry1 and cry2 genes, including the two isolates with high toxicity on S. litura. This study contributed to the local Bt collection in Vietnam. The obtained isolates with high toxicity on S. litura could be utilized in applications to control lepidonteran insect pests.