Toxicity of Bacillus thuringiensis to laboratory populations of the olive fruit fly (Dacus oleae)
A survey of Bacillus thuringiensis recovered from the environments of olive groves in Greece was carried out. Of 80 soil samples, 24 were found to contain B. thuringiensis with parasporal crystal inclusions; these were tested for toxicity against the olive fruit fly (Dacus oleae). Mortality levels of larvae caused by the different isolates varied from 7 to 87%. Higher levels of mortality were observed if a mixture of relatively pure crystals and spores was used compared with the mortality resulting from either fraction alone. We were able to show that the toxicity of the most active isolate is likely to be specific for D. oleae.
The occurrence, biodiversity and toxicity of Bacillus thuringiensis strains isolated from the insect pest Lymantria dispar (Poland).
The aim of this investigation was to survey the occurrence, biodiversity, and toxicity of Bacillus thuringiensis strains originating from dead caterpillars of the forest pest, Lymantria dispar (Lepidoptera). Morphological, biochemical, and microscopic identification of isolates from the insects showed the presence of five different Bacillus species, including 2% of B. thuringiensis. Based on the biochemical profiles, the B. thuringiensis were determined to be B. thuringiensis finitimus-like and B. thuringiensis alesti-like bacilli. Both produced spherical inclusions composed of three or five protoxins. The molecular weights of these proteins varied from 20 to ca. 64 kDa. Mixtures of spores/inclusions of the B. thuringiensis were tested for their toxicity against larvae of Drosophila melanogaster. The mortality levels of the larvae caused by these spores and crystalline inclusions varied from 5 to 15%. The lethal doses (LD50) of these isolates against D. melanogaster were 8.8 x 10(12) spores/ml for B. thuringiensis finitimus and 1.3 10(18) spores/ml for B. thuringiensis alesti.
Purification of the insecticidal toxin from the parasporal crystal of Bacillus thuringiensis subsp. kurstaki.
Abstract The insecticidal toxin of Bacillus thuringiensis subsp. kurstaki was isolated from parasporal crystals. The toxin, which is stable for several months, is a glycoprotein with an apparent molecular weight of 68,000 that is generated upon solubilization and activation of a higher molecular weight protoxin (MWapp = 1.3 × 105) at alkaline pH. The toxin was purified by gel filtation and anion exchange chromatography and its molecular weight was established by gel filtration chromatography and SDS polyacrylamide gel electrophoresis.