Investigation of Mosquito-Specific Larvicidal Activity of a Soil Isolate of Bacillus thuringiensis serovar canadensis

The LC₅₀ value of alkali-solubilized parasporal inclusion proteins of a Diptera-specific strain, belonging to Bacillus thuringiensis serovar canadensis, was 2.4 μg/ml for larvae of the mosquito, Aedes aegypti. A significant loss in larvicidal activity occurred when solubilized inclusion proteins were treated with A. aegypti larval gut extract, silkworm (Bombyx mori) larval gut juice, and the proteinase K. Approximately 90% of the larvicidal activity was destroyed upon treatment with proteases in 30 min. The parasporal inclusion was composed of major proteins of 65, 53, and 28 kDa and some other minor proteins. Proteolysis profiles showed that the 65-kDa major protein is highly sensitive to proteases. Purification experiments with DEAE-Toyopearl column chromatography revealed that the 65-kDa protein is responsible for the mosquitocidal activity of this strain. The LC₅₀ value of the purified protein was 5.4 μg/ml. Received: 2 December 1996 / Accepted: 7 January 1997