Toxicity of different isolates of Bacillus thuringiensis Berliner to the larvae of diamondback moth, Plutella xylostella (Linnaeus)

Bacillus thuringiensis Berliner (Bt) has been successfully employed in pest management programmes both in agriculture and public health. Efficient isolation methods and intensive screening have yielded novel isolates of Bt, more potent than the available ones. In the present study, LC₅₀ values for 18 isolates of Bt obtained from different sources, viz. soil, leaf, seed dust and insect cadavers were determined on five-day-old larvae of P. xylostella. Among the 18 isolates (five, two and one from soil, insect cadavers and seed dust, respectively), were more toxic to the larvae of P. xylostella. The relative toxicity values for the above isolates ranged from 1.0 to 5.5 times as compared to the International standard, HD-1-S-1980. The more potent isolates could be used in developing sprayable formulations and also a source of novel crystal toxin genes.