Regarding to the potential adverse environmental effects of chemical insecticides, some alternative approaches like biological control agents have been proposed to address this problem. One of the promising alternative is use of Entomopathogenic Bacteria such as Bacillus thuringiensis (Bt). During sporulation, Bt produces crystalline inclusion proteins comprising different groups of cry and cyt toxins. Cry proteins target insects in the orders Lepidoptera, Diptera, Coleoptera and Hymenopterans as well as nematodes. High toxicity to Diptera has been reported for Cyt proteins. As individual Cry toxin has a defined spectrum of insecticidal activity, usually restricted to a few species in one particular order, recently researchers have been reported a novel Bacillus thuringiensis vegetative insecticidal protein (VIP) with a wide spectrum of activities against lepidopteran insects. Besides the Cry and Cyt proteins, which are the focus of this review, Bt produces various virulent factors including secreted insecticidal protein toxins (exotoxins). Strain engineering efforts have continued to extend the Bt host range.

Strain improvement led to the replacement of many of the early products with new Bt strains that were more potent than their predecessors, and the search for new and better strains continues to this day. Transgenic crop plants (Bt crops) have been commercialized that express several Cry and/or cyt from Bt. These plants are resistant against a wide range of insect species. This strategy has several advantages over chemical pesticides that accepted and adapted by many developed and developing countries.