Includes bibliographical references.

Cole crops are major vegetable crops of Meghalaya contributing significantly to the agriculture of the state. However, the cabbage butterfly, Pieris brassicae is an important pest of the cole crops causing a significant loss by diminishing the production as well as market value of the produce. Therefore, the management of this pest is crucial for which the adoption of Bacillus thuringiensis is an effective, ecofriendly and sustainable approach as compared to the conventional methods. Bt is a naturally occurring gram positive, rod shaped, motile, facultative anaerobic and also spore forming bacterium found in soil which is widely used as an eco-friendly biopesticide against insect pests in agriculture and forestry. The bacterium is renowned for its high specificity and environmental safety. In the present investigation, the isolation and characterisation of diverse isolates of Bt from Manipur region and the evaluation and shortlisting of novel Bt isolates against Cabbage butterfly, Pieris brassicae (Linnaeus) were undertaken. A total of 10 Bt strains were isolated from the Manipur region. Among them, two strains each from the districts of Bishnupur, Kakching and Noney and one each from the districts of Churachandpur, Kangpokpi, Senapati and Tamenglong were isolated. The isolates exhibited the characteristic creamy white colour, elevated or flat colonies with dry and rough texture. The phase contrast and electron microscopy studies revealed the presence of crystals with smooth spherical, spherical with undulating surface and deflated balloon like structures. The cry gene content of the isolates was detected by PCR analysis revealing the presence of cry1, cry1A and cry1IA in them. The bioassay studies have resulted in four isolates (MKAKG-1, MBNPR-1, MBNPR-2 and MSNPT-1) which exhibited 100% mortality in the P. brassicae larvae. When compared to the reference strains, two of the novel isolates viz., MKAKG-1 and MBNPR-1 exhibited higher mortality. The median lethal concentrations of these isolates are 2.8×105 (95% FL, 5.5×104 -1.4×106) and 3.0×105 (95% FL, 5.8×104 - 1.6×106) respectively. From the present study, it can be concluded that MKAKG-1 and MBNPR-1 are potential Bt strains that can be used effectively against P. brassicae. These isolates can be further used for developing and producing new active bioinsecticides which can be integrated with the management program of lepidopteran pests.