3. Risk Assessment of Bt Transgenic Crops

The global demand, likely to escalate for at least another 40 years, requires a multifaceted strategy to ensure food security. Augmentation of crop yields in a sustainable manner is essential. Pests destroy on an average 14–25% of the total global agricultural production. Biopesticides are an important component of integrated pest management (IPM) strategies employed for minimization of insect pests-incurred crop yield losses as also for reduction of use of environmentally harmful chemical pesticides. Bacillus thuringiensis (Bt) is an aerobic, gram-positive, spore-forming bacterium producing crystal proteins (Cry), which are selectively toxic to target insects. Cry proteins act by insertion into the microvillar brush-border membranes in the midgut of susceptible insects, leading to disruption of osmotic balance, lysis of epithelial cells and eventually death of insect. Some Bt strains additionally secrete vegetative insecticidal proteins (Vips), which cause toxicity in susceptible insects by midgut epithelial cell lysis and gut paralysis. Bt has been used as a microbial biopesticide for the past five decades because of the advantages of specific toxicity against target insects, lack of polluting residues and safety to non-target organisms, and accounts for 95% of the 1% market share of biopesticides in the total pesticide market. However, the use of Bt microbial biopesticide formulations has been rather limited due to the problems of narrow host range, low persistence on plants and inability of foliar application to reach the insects feeding inside the plants, notwithstanding several biotechnological approaches for the development of improved Bt biopesticides. Bt transgenic crops have been developed to overcome the problems of Bt biopesticides and for more effective insect control. Risk assessment in relation to certain concerns raised about environmental and food safety of Bt transgenic crops has been addressed in this chapter.