In-vitro toxicity profile of native Bacillus thuringiensis isolates from Punjab soils against blister beetle, Mylabris pustulata (Thunberg) in pigeonpea

The present study aimed at initiating the collection of indigenous Bacillus thuringiensis strains from Punjab, determining diversity among them and identifying the potential strains active against blister beetle, Mylabris pustulata. To accomplish this, B. thuringiensis was investigated from soils of 12 districts of Punjab, representing diverse agroclimatic zones and geographical areas of the state. A total of 71 samples were collected from various districts to isolate native B. thuringiensis (Bt) strains. Phenotypic characterization and identification of recovered Bt isolates was accomplished on the basis of morphological characteristics of colonies and the presence of parasporal crystal proteins. Bt index was highest in the samples collected from the districts of Bathinda, Faridkot, Ferozepur and Jalandhar and lowest in the samples collected from Moga district. When viewed under Phase-Contrast microscope under 100X(Oil immersion objective), Btisolateswere found to exhibit different crystal shapes (bipyramidal, elliptical & cylindrical) and different spore positions (terminal, sub-terminal, para-terminal, para-central and central). In-vitro bioassays against adult beetles indicated that two native Bt isolates, viz. LDH3-2 and FDK3-3 were found to be promising in terms of registering the highest beetle mortality, lower flower consumption and beetle weights. Identification of any such native isolate(s) effective against M. pustulata will play a key role in insect pest management in pigeonpea as well as in diminishing the use of chemical insecticides.