Abstract

The toxicity effect of Bacillus thuringiensis against Plutella xylostella is well established. However, effective B. thuringiensis strain especially local isolate is not well tested. In this study local strain B. thuringiensis subspecies kurstaki, SN5 was assessed for its effectiveness against P. xylostella 3rd instar larvae. Other factors such as spore germination, spore coat, L-alanine-adenosine (LAA) and streptomycin were evaluated with their possible effects on the toxicity of B. thuringiensis cry protein. The result of the study showed that SN5 spore exhibit higher toxicity than the commercial strain, HD-1. L-Alanine-adenosine not only improves rate of spore germination but also synergy effect of spore-crystal mix by increasing toxicity of the mixture. These results demonstrating the potential of local isolate in managing P. xylostella and its potential effect can be increase by adding LAA.

Key words: Bacillus thuringiensis, cry-like protein, L-alanine-adenosine, Plutella xylostella, streptomycin, toxicity.