The insecticidal bacterium Bacillus thuringiensis ]Berliner is the most successfully commercialized biocontrol agent, currently used in many countries to control a number of lepidopteran and coleopteran pests of vegetables, forests and field crops and to control the larvae of many species of vectors, mosquitoes and blackflies. The success of B. thuringiensis (Bt) can be attributed to the high efficacy of its insecticidal proteins and the existence of a variety of proteins that are effective against a wide range of important pests.
Many synthetic pesticides are used for protecting plants and crops from unwanted insects and pests. Most of them contain harmful chemicals and toxins that not only kill the unwanted pests but also many beneficial insects. They are also potentially harmful for domestic animals who might consume them by mistake and for humans who consume the food sprayed with such pesticides. Alternatively, biopesticides are derived from such natural sources such as animals, plants, bacteria and certain minerals. Microbial pesticides, for example, consist of microorganisms like bacteria, fungi, virus or protozoa that have natural abilities to control the growth of certain weeds or kill specific insects. It was not until after the Second World War, when the first problem with synthetic pesticides turned up, serious attempts were made to establish Bacillus thuringiensis as a microbial pesticide. It has a toxic effect on insects due to the δ endotoxin, a protein produced by the bacterium during sporulation. This feature of the bacterium was harnessed as a means of crop protection back in the middle of the last century when the first Bacillus thuringiensis preparations were marketed as bio-insecticides.
Bt was used as an insecticide in 1920's and as a commercial pesticide in France during 1938. In 1950s, it was sold in the United States as an insecticide. In 1961, Bt was registered as a pesticide in the United States. In 1995, the market volume of Bt preparations was estimated at 90 million US dollars and 67 preparations were registered worldwide. Bt represents about 1% of the total insecticide market worldwide but this is changing to a higher percentage as the Bt toxin genes are genetically engineered into crop plants like cotton and corn. The crystal proteins of Bt have been studied for their insecticidal properties and their high natural levels of production. Other kinds of insecticidal proteins have also been described in Bacillus thuringiensis among which are the vegetative insecticidal proteins or Vip proteins and surface layer proteins or S-layer proteins. Common insect targets are moths, mosquitoes, blackflies, beetles, hoppers, aphids, wasps and bees as well as nematodes.
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