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.
Factors affecting the larvicidal activity of Bacillus thuringiensis israelensis toxin for Trichostrongylus colubriformis (Nematoda).
Abstract The larvidical activity of crystals from Bacillus thuringiensis israelensis for the nematode Trichostrongylus colubriformis was not increased by storage for 6 days or moderate heat. However, treatment with trypsin increased the activity. Larvicidal activity was inhibited by cupric or ferric chloride. Gamma or ultraviolet irradiation had no effect on the toxin. First-stage larvae of the nematode also were killed by the B. thuringiensis israelensis toxin. Larvidical effects of the toxin were reduced when in vitro assays were conducted at 4°C. Toxin from bacteria at various periods of cultivation had similar lethal effects on eggs. Growth of the bacterium during the in vitro assay had no relation to resultant toxicity for eggs. The toxin eluted through a reverse-phase Sep-Pak, but was retained by membrane filters with a pore size of 0.8 μm or less. Dialysis of the B. thuringiensis israelensis toxin in sequentially smaller pore size membranes caused no significant change in larvicidal activity. No larvicidal activity was found in ultrafiltrates after passage through filters with molecular weight cutoffs from 500 to 10,000. Toxicity of B. thuringiensis israelensis was reduced by heating to 100°C for 1 hr, autoclaving, or addition of Penicillin G or streptomycin to the eggs' medium. B. thuringiensis kurstaki had no effect on the in vitro toxicity of B. thuringiensis israelensis for nematode eggs, but B. thuringiensis israelensis reduced the toxicity of low doses of B. thuringiensis kurstaki.
Toxicity of Bacillus thuringiensis spores to the tobacco hornworm, Manduca sexta
Toxicity of Bacillus thuringiensis spores to the tobacco hornworm, Manduca sexta, is described. The numbers of larvae killed were in relation to spore dry weight. At a surface application of 6.8 ng/cm2, there was an 85 percent survival, but less than 50 percent survived at 68.2 ng/cm2. Striking similarity of spores to parasporal crystals is revealed by slope of mortality curves, inhibition of stadial growth, and 50 percent lethal dose values based on protein content.