Includes bibliographical references.

Maize (Zea mays L.) is the 3rdmost important cereal crop in India (production, 27.64 million tonnes). In NE India productivity of maize is 2298 kg/ha with Meghalaya at 7thposition. Fall armyworm (Spodopterafrugiperda) is an invasive polyphagous pest with maize as its most preferred host. FAW in unmanaged fields can cause 21-53% loss in annual maize production. The problems of development of resistance, pest resurgence, harmful effects on environment etc. compromises the effectiveness of conventional methods of pest control. Therefore, the present investigation was undertaken to assess the adoption of Bacillus thuringiensis (Bt) in pest management with the objective to isolate and characterize diverse isolates of Bt from Meghalaya and evaluating their toxicity against FAW. A total of 77 samples were collected from 58 different locations representing 15 Blocks within 6 districts of Meghalaya. Two isolation methodologies were compared showing that ‘Sodium acetate’ method was most efficient for isolation of Bt from soil. A total of 571Bt like colonies were obtained out of which 24 strains were identified as Bt through morphological, microscopical and molecular characterization. Colony morphology studies revealed that maximum among the 24 isolates had circular whole colony form, creamy white colour, raised elevation, dry rough texture and entire colony margins. CBB staining and phase contrast microscopy revealed the presence of parasporal bodies in all the 24 isolates. Molecular identification was carried out using universal primers for 16S rRNA gene (27F and 1492R primers) and for cry1 and cry2 (Lepidopteran specific), cry3, cry4 and cry9 gene. The sequences of 24 Bt isolates were compared for homology using NCBI BLAST and phylogenetic tree was prepared. The 24 native Bt isolates showed the presence of cry1 gene and were carried on for bioassay studies. Initially, selective bioassays were carried out with spore concentration of 3×108 cells/ml to screen the most effective strains against FAW. Results revealed that none of 24 B tisolates obtained from Meghalaya are effective against FAW, whereas, only two out of three reference strains (4D1 Bt serovar. kurstaki and 4J3Btserovar.aizawai) showed 100% mortality against FAW. Concentration based assays using 4D1 and 4J3 strains were carried out revealing that 4J3 was effective than 4D1 with a lower LC50 value of 3×104spores/ml. Comparison studies for 4D1 and 4J3 revealed that 106 ,107 ,108 and 109 cells/ml concentrations are at par. Comparative studies on mean mortality at 96 hrs revealed that there was no significant difference between 4D1 and 4J3. However, 4J3 had a lower LC₅₀ value. cry gene analysis revealed that 4J3 harboured cry1, cry2, cry9, cry1Ac, cry1A, cry1B, cry1D, cry1IA and vip3a genes and 4D1 harboured cry1, cry2, cry1Ac, cry1A, cry1B, cry1IA and vip3a genes. It was concluded that Bt is not much efficient against Armyworm complex (Spodoptera spp.) with S. frugiperda being least sensitive to Bt class of toxins as per previous published reports. Additionally, factors that affects the efficiency of Bt viz., solubility of crystal proteins in the midgut, genetic variability of population of the insect, genetic diversity of Bt communities (type of proteininclusions), differences in toxinexpression, synergistic effects between some cry toxins, cry gene profile should be considered before developing a screening procedure against single target pest for promising Bt strains.