MOHAN, MNAGARAJU, M C2023-01-052023-01-052022-12-31Th-12820https://krishikosh.egranth.ac.in/handle/1/5810191268The tomato pinworm, Tuta absoluta and the maize fall armyworm, Spodoptera frugiperda are the recent invasive insect pests that damages tomato and maize in India. In the absence of effective natural enemies, microbial control based on indigenous Bacillus thuringiensis strains is viewed as a viable alternative to synthetic insecticides. The present effort yielded 70 B. thuringiensis isolates by processing 300 samples collected from different states of India. All the isolates were subjected to morphological and toxicological characterization. Among the 70 isolates, 67 isolates showed bipyramidal type of crystal and the remaining three isolates showed square, elliptical and spherical crystal shapes, respectively. Detailed probit dose-mortality bioassays were conducted for 15 effective B. thuringiensis isolates. The LC50 values for the isolates tested against the larvae of T. absoluta ranged between 16.16 and 76.84 ppm at 72h. Similarly the LC50 values for the isolates tested against the larvae of S. frugiperda ranged between 56.82 and 194.59 ppm at 72h. The isolates Bt-Oa1 and Bt-257 were selected for further field testing based on their least LC90 values. On tomato, Bt-Oa1 WBF @ double the dose of LC90 (4.4 ml/lit) exhibited highest per cent larval reduction (74.60 %), similarly on maize, Bt-Oa1 WBF @ double the dose of LC90 formulation (5.2 ml/lit) exhibited highest per cent larval reduction (70.86 %). The study concluded that formulations based on indigenous B. thuringiensis could be effectively used for the management of T. absoluta on S. frugiperda tomato and maize crops respectively.EnglishThesis