Evaluation of indigenous entomopathogenic bacteria against some lepidopterous pests

Abstract

newline Insect cadaver, soil and FYM samples from different districts of Himachal Pradesh (India) were used for the isolation of entomopathogenic bacteria. The bacteria associated with insect cadavers were screened for their pathogenicity against lepidopterous pests and resultant isolates were identified using morphological, biochemical and cultural characteristics. The promising isolates were also studied using molecular techniques and their comparative intrinsic toxicity with reference strains was evaluated. Out of 70 bacterial isolates obtained from 59 insect cadavers, 11, 7, 5 and 14 isolates showed pathogenicity against 2nd instar larvae of Plutella xylostella L., Helicoverpa armigera (Hübner), Spodoptera litura (Fabricius) and Trichoplusia ni (Hübner), respectively. Two isolates namely, KaCc3 and KaMs2 were found promising against lepidopterous insects and resulted in high mortality (gt80%) comparable to reference strains. Majority of entomopathogenic isolates (56.25%) were identified as Bacillus spp. followed by Serratia spp. (12.50%). B. thuringiensis contributed 12.50 per cent of total entomopathogenic isolates, whereas three entomopathogenic isolates could not be identified. The sequences of 16S rDNA of promising isolates KaCc3 and KaMs2 were submitted to GenBank, NCBI with accession numbers KC503921 and KC503922, respectively, and confirmed as B. thuringiensis. SDS-PAGE analysis of parasporal crystal proteins showed distinct protein pattern with isolate KaCc3 as compared with reference strains. B. thuringiensis could not be isolated from any of the soil and FYM sample, whereas two isolates were obtained from insect cadavers and the overall Bt index was calculated as 0.001 in Himachal Pradesh. The LC50 and LT50 were determined to be 1.24 × 106 and 1.66 × 107 spores/ml, 39.52 and 58.28 hours for isolate KaCc3 and KaMs2, respectively, against 2nd instar larvae of P. xylostella. KaCc3 and KaMs2 registered LC50 and LT50 of 1.08 × 107 and 4.30 × 107 spores/ml, 41.04 and 56.53 hours, respectively, against 2nd instar larvae of H. armigera. For S. litura, the LC¬¬50 and LT50 were determined to be 1.07 × 107 and 2.46 × 108 spores/ml, 41.84 and 56.27 hours for KaCc3 and KaMs2, respectively, against 2nd instar larvae. Indigenous isolate KaCc3 had higher intrinsic toxicity against lepidopterous pests as compared to reference strains PDBC 1 and MTCC 868, but lower than reference strain HD 1. newline newline