Background: The rising demand for food production along with the concerns regarding the injudicious use of chemicals in pest management has paved way for the alternatives that could promise sustainable pest management. Bacillus thuringiensis Berliner (Bt), a soil bacterium, is a potential biopesticide with its ability to produce crystal toxins that are insecticidal in nature. Main body: This article provides an insight into the diverse Bt toxins and their applications as biopesticides in pest management. The selective action of Bt towards target organism is based on its specific interactions with the insect gut receptors. The significance of Bt in the management of lepidopteran, coleopteran, hemipteran, dipteran and nematode pests of crops and livestock through its mode of action is extensively reviewed. Conclusion: Besides being a promising pest control option, the challenges faced through resistance development, variation in susceptibility across species and non-target effects of Bt are also discussed. Proactive approaches and multiple modes of action can mitigate this issue.

A synthetic cry2AX1 gene, consisting sequence of cry2Aa and cry2Ac genes, driven by green tissue specific rbcS promoter was used to develop insect resistant marker-free transgenic rice events. The gene of interest cry2AX1 and the selectable marker gene hpt were present in two independent T-DNAs of the Agrobacterium strain, C58C1. Seventy seven hygromycin and GUS positive T₀ transgenic plants were recovered. Among them, 48 were found to be co-transformed with cry2AX1. The Cry2AX1 protein expression level in T₀ transgenic events ranged from 0.027 to 0.110 μg/g of fresh leaf tissue. The toxicity level of Cry2AX1 protein was assessed through in vitro bioassay against target insects. The larval mortality ranged from 46.66 to 66.67 per cent against rice leaffolder (C. medinalis) while it ranged from 60 to 100 per cent against rice yellow stem borer (S. incertulas) in T₀ transgenic plants. A marker free transgenic event, which expressed 0.043 μg/g of Cry2AX1 in fresh leaf tissue exhibited 45 and 55 per cent larval mortality against rice leaffolder and rice yellow stem borer, respectively in T₂ generation.

Development of transgenic Bt crops with stable and high level of Bt protein expression over generations under different environmental conditions is critical for successful deployment at field level. In the present study, progenies of transgenic cotton Coker310 event, CH12 expressing novel cry2AX1 gene were evaluated in T3 generation for stable integration, expression and resistance against cotton bollworm, Helicoverpa armigera. The cry2AX1 gene showed stable inheritance and integration in the T3 progeny plants as revealed by PCR and Southern blot hybridization. The expression of Cry2AX1 protein on 90 days after sowing (DAS) was in the range of 1.055 to 1.5 µg/g of fresh leaf tissue except one plant which showed 0.806 µg/g of fresh leaf tissue and after 30 days (i.e., on 120 DAS) three plants recorded in between 0.69 to 0.82 µg/g and other plants are in range of 0.918 to 1.058 µg/g of fresh leaf tissue. Detached leaf bit bioassay in T3 progeny on 110 DAS recorded mortality of 73.33 to 93.33 per cent against H. armigera and severe growth retardation in surviving larvae. These results indicate that the expression of chimeric cry2AX1 is stable and exhibits insecticidal activity against H. armigera in T3 progeny of CH12 event of transgenic cotton.