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WHAT IS BT B. thuringiensis

Bt stands for B. thuringiensis which is closely related to B.cereus, a soil bacterium, and B.anthracis, the cause of anthrax. Upon sporulation, B. thuringiensis forms crystals of proteinaceous insecticidal d-endotoxins (called crystal proteins or Cry proteins), which are encoded by cry genes. In most strains of B. thuringiensis, the

pH of their digestive tract activates the toxin. Cry toxin gets inserted into the insect gut cell membrane, forming a pore. The pore results in cell lyses and eventual death of the insect. B. thuringiensis-based insecticides are often applied as liquid sprays on crop plants where the insecticide must be ingested to be effective. The solubilized toxins are thought to form pores in the midgut epithelium of susceptible larvae. Recent research has suggested the midgut bacteria of susceptible larvae are requ i r e d f o r B. thuringiensis insecticidal activity. Typically, exposure occurs through the consumption of plant parts, such as pollen or plant debris, or through Bt ingestion by their predatory food choices.

cry genes are located on the plasmid. Cry toxins have specific activities against insect species of the orders Lepidoptera (moths and butterflies), Diptera (flies and mosquitoes), Coleoptera (beetles), Hymenoptera (wasps, bees, ants and sawflies) and nematodes. Thus, B. thuringiensis serves as an important reservoir of Cry toxins for production of biological insecticides and insect-resistant genetically modified crops (gmo).

The most publicized problem associated with Bt crops is the claim that pollen from Bt-maize could kill the monarch butterfly. Bt containing maize genes were contaminating maize in its center of origin. Colony collapse disorder (CCD) is affecting bee hives all over North America. Initial speculation on possible causes ranged from new parasites to pesticide used on the Bt resistant transgenic crops.

When insects ingest toxin crystals, the alkaline It has been found Bt-Cotton is killing India's sheep.

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