Characterization of various Bacillus thuringiensis strains having larvicidal activity on Chilo partellus first-instar larvae, after culture on cost-effective medium, in Kenya

Abstract

Bacillus thuringiensis strains are widely used in many larvicidal pest control programs. However, the large-scale production of these biolarvicides is very expensive due to the high cost of the production synthetic medium. In this study, we developed cost-effective media, based on locally available raw materials namely legumes, potato, and whey. The optical density, protein concentration yield, sporulation and Chilo partellus larvicidal action were studied by growing bacterial strains in these waste product and in comparison with the conventional medium (NYSM). Protein concentration yield of 27.60 μg/ ml, spore count of 5.60 × 108 and Chilo partellus larvicidal activity (LC50) of 78 μg/ l against first-instar larvae were obtained with a 72 h culture of this bacterium. Production of Bt Insecticidal Crystal Proteins in NYSM was comparable to the test media and mean values were not significantly different for spore counts: F (media) = 25.19 P>0.01. One-way ANOVA (repeated measures) difference in percentage larval mortalities of Bacillus thuringiensis subspecies kurstaki (F = 26.88, P>0.05) and Bt isolates was not statistically significant. The SDS-PAGE profiles indicated that spore-crystal product from each treatment consisted of proteins with molecular weights of approximately 110-120 kDa and 60-70 kDa. Therefore the investigation suggests that legume, potato and whey-based culture media are more economical for the industrial production of Bt Insecticidal Crystal Proteins.