Optimization of fermentation parameters and in vitro efficacy of native Bacillus thuringiensis isolates against Spodoptera litura

Abstract

Insect pests are the major cause for damage to agricultural crops. Current strategies aimed to reduce crop losses primarily rely on chemical pesticides. Microbial pesticides and transgenic crops with intrinsic pest resistance are considered to be a promising alternative developed over the last few decades. Bacillus thuringiensis (Bt) is a gram-positive, sporeforming, soil bacterium which produces different insecticidal crystal proteins encoded by cry genes and is an effective tool to control insects, mites, nematode, etc. Native isolates of Bt (CT-1, CT-2, TOB-1) recovered from farms of Anand Agricultural University checked with standard strains of Bt var. kurstaki and Bt HD-73. Bioassay of the Bt isolates proved that CT-2 was more effective than all other isolates against the S. litura. The LC 50 value of CT-2 was 4.99 × 10 6 (4.99 µl) as compared with TOB [1.41 × 10 7 (14.10 µl)] and Btk and HD-73 [3.85 × 10 7 (38.50 µl)] at 96 h. It was observed that the percent larval mortality increased with a consequent increase in dose as well as time up to 168 h. Mass production of native Bt isolates showed that combination of molasses and corn steep liquor was found best followed by molasses alone and combination of molasses, corn steep liquor, rice bran, and wheat bran.