Role of the parasporal body in causing toxicity of Bacillus thuringiensis toward Aedes aegypti larvae

Abstract

Bacillus thuringiensis strain HD-1 was found effectively to kill three different types of mosquito larvae. The LC50s of the bacterium toward Aedes aegypti, Anopheles dirus, and Culex quinquefasciatus were 1.2 × 105, 1.1 × 104, and 8.2 × 105bacteria/ml, respectively. However, this strain did not show any toxic effects to the predeceous mosquito larvae of Toxorhynchites splendens. The toxic factor was believed to be associated with the parasporal body of the bacterium, since a sporgenic but acrystalliferous mutant of HD-1 (strain HD-1S) lacked the ability to kill larvae. Also, an oligosporogenous but crystalliferous mutant (strain R-201), which was selected from rifampicin resistant strains of B. thuringiensis HD-1, demonstrated the same level of toxicity toward A. aegypti larvae as the parent strain even though its cultures contained 3000-fold fewer spores than cultures of the parent strain. Alkaline extracts (0.1 n NaOH for 1 hr) of crude crystal preparation from strain R-201 retained the toxicity toward A. aegypti larvae. The results suggested strongly that the larvicidal factor(s) of B. thuringiensis were contained in its crystalline body. © 1982.