Relative efficacy of two subspecies ofBacillus thuringiensis, available as commercial preparations in market, on different stages of a lepidopteran pest,Spodoptera litura(Fabricius)

Abstract The present study compares the efficacy of two different subspecies of Bacillus thuringiensis viz. aizawai and kurstaki, available as commercial preparations in market against different stages of Spodoptera litura. Leaf-dip bioassay was done to calculate the LC50 values of both the preparations, while microbiological analysis and total protein content estimation were also performed to co-relate the results. B. thuringiensis aizawai was found to be more effective (LC50 values being 0.505, 1.121, 5.009, 6.706 for 1st, 2nd, 3rd, and 4th instar, respectively) than kurstaki (LC50 values being 1.121, 3.974, 6.897, 9.471 for 1st, 2nd, 3rd, and 4th instar, respectively). The efficacy was found to depend upon the number of viable spores in a particular preparation as well as on the total protein content of that particular subspecies. The preparation containing B.t.a was more effective because its viable spore counts as well as total protein content values (at different time intervals) were higher as compared to the preparation containing B.t.k. The growth rates for both the subspecies were almost the same, which didn't seem to affect their efficacy on S. litura.