Gunnel Carlberg

Testing fly resistance to thuringiensin produced by Bacillus thuringiensis, serotype H-1

Abstract A Bacillus thuringiensis preparation used for microbial control of flies was tested for development of resistance to thuringiensin in Drosophila melanogaster. A 10-fold resistance developed in 30 generations in fruitflies reared in medium containing 0.3 to 1.0% preparation but did not rise from generations F30 to F70. A 6-fold resistance was obtained at 0.2 to 0.5% preparation. Flies reared in 2 and 3% preparation were very weak and did not develop resistance during selection. On the contrary, they died out in generation F58. Tests with fruitflies resistant to chemicals have shown that there is no cross-resistance between chemicals and thuringiensin. These data are discussed relative to the use of thuringiensin in controlling flies.

Studies on Bacillus thuringiensis H-14 strains isolated in Egypt-V. Composition and toxicity of the mosquitocidal parasporal inclusions.

Parasporal inclusions of Bacillus thuringlensis H-14 strains M1 and S128 were characterized by solubilization, electron microscopy, polyacrylamide gel electrophoresis, amino acid analysis and insecticidal activity. Inclusions of both strains are composed largely of protein with 8 to 9% carbohydrate. Amino acid analysis of the purlfied inclusions revealed that the two strains produce inclusions that are closely related to each other but significantly different from lepidopteran-toxic B. thuringiensis parasporal crystals. The LC50 values of the purlfied inclusions of strains M1 and S128 were 3.4 and 2.9 ng/ml, respectively, for fourth instar larvae of Aedes aegypti. Inclusions from strain M1 were resolved into two inclusion bands on the basis of their densities possibly formed as a result of disruption of some envelopes during sonication. Both inclusion types contained proteins of approximately 27, 38 and 66 kDa. The heavlest and more predominant type had an envelope and was either spherical or irregular being composed of several subunits which varied in shape, size and staining densities. The LC50 value was 2.2 ng/ml and the major protein was of approximately 27 kDa. The lightest inclusions type did not have an envelope and showed clear crystal lattices. They were 10 times less toxic to A. aegypti larvae, as compared to the heavy-type inclusions and contained major protein of approximately 66 kDa.

Algae in mosquito breeding sites and the effectiveness of the mosquito larvicide Bacillus thuringiensis H-14

The presence of cyanobacteria generally decreased the effectiveness of Bacillus thuringiensis H-14 (BTI) as a mosquito larvicide. The effect was more pronounced when the mosquito larvae were exposed to BTI in the presence of several cyanobacterial strains. No synergistic or antagonistic effect between the δ-endotoxin from BTI and the hepatotoxin from cyanobacteria was seen. Neurotoxic cyanobacterial strains caused very fast paralysis in mosquito larvae; the decreases in the effectiveness of BTI when tested in combination with a neurotoxic strain might be due to the effect of this paralytic action on the feeding rate of the mosquito larvae.