Selection and Characterization of Bacillus thuringiensis Strains with Biological Activity against Lycoriella ingenua

In order to use Lycoriella ingenua, a major pest of mushroom cultivation, as a biological control agent, the biologic activity of Bacillus thuringiensis strain, which is toxic to diptera insects, was examined. The larvicidal activities of the strain against the larvae of L. ingenua and Bradysia agrestis as target agricultural pest species, and Aedes albopictus, Aedes togoi, and Culex pipiens pallens as sanitary pest species were examined. B. thuringiensis subsp. darmstadiensis and B. thuringiensis subsp. kyushuensis CAB464 strains that showed 90% or higher larvicidal activities against the five species of pests, of which the biologic activity was tested, were selected. Between the two selected strains, the B. thuringiensis subsp. kyushuensis CAB464 strain showed higher larvicidal activity against L. ingenua larvae, with an LC₉₅ value of 1.6×10⁶ (cfu/ml). In addition, the LC₉₅ value of B. thuringiensis subsp. darmstadiensis strain was shown to be 3.5×10⁶ (cfu/ml), which was higher larvicidal activity than the control strain B. thuringiensis subsp. israelensis. In an SDS–PAGE analysis of the endotoxin protein bands of the two B. thuringiensis strains that showed high toxicity against diptera pest, the two strains showed the same three bands at 150, 70, and 50 kDa, and in trypsin reactions, the two strains again showed the same pattern of being at approximately 65 and 60 kDa. In a PCR analysis for the crystal proteins of the two strains, it was identified that both strains had cyt2Aa gene. Meanwhile, in plasmid DNA patterns, five plasmid DNA bands were identified in B. thuringiensis subsp. darmstadiensis strain and nine plasmid DNA bands were identified in B. thuringiensis subsp. kyushuensis CAB464 strain.