Insect pest management in agriculture is important to safeguard crop yields and productivity. A large number of chemical insecticides that effectively control insect pests have been proven to be harmful to human health and environment. There is a need to reduce the dependence on pesticides by using safer alternatives to manage insect pests. Many insecticidal proteins and molecules are available in nature, which are effective against agriculturally important pests but innocuous to mammals, beneficial insects and other organisms. Insecticidal proteins present in the soil borne bacterium, Bacillus thuringiensis (Bt), which has demonstrated its efficacy as a spray formulation in agriculture over the past five decades, have been expressed in many crop species with positive results (Kumar et al., 1996). Bt-transgenic crop species (cotton, corn, rice, tomato and potato) have been commercialized with substantial benefits to the farmers (Kumar 2003).
Bt is a gram-positive, aerobic, endospore-forming bacterium belonging to morphological group I along with Bacillus cereus, Bacillus anthracis and Bacillus laterosporus. All these bacteria have endospores. Bt, however, is recognized by its parasporal body (known as the crystal) that is proteinaceous in nature and which possesses insecticidal properties. The parasporal body comprises of crystals varying in size, shape and morphology. The crystals are tightly packed with proteins called protoxins or d-endotoxins. The first record on Bt goes back to 1901, when a Japanese microbiologist Ishiwata discovered a bacterium from diseased silkworm larvae, which he named Bacillus sotto. Between 1909 and 1912, Berliner, working at a research station for grain processing in Germany, investigated an infectious disease of the Mediterranean flour moth and described a spore-forming bacterium as the causative agent and designated it as B. thuringiensis.
There are many subspecies and serotypes of Bt with a range of well-characterized insecticidal proteins or Bt toxins (delta-endotoxins). At present it has been estimated that over 60,000 isolates of Bt are being maintained in culture collections worldwide. Known Bt toxins kill subsets of insects among the Lepidoptera, Coleoptera, Diptera and nematodes. The host range of Bt has expanded considerably in recent years due to extensive screening programs. Currently more than 150 different genes encoding Bt toxins have been cloned. Recent information about Bt toxins/genes can be obtained from