Characterization of native Bacillus thuringiensis strains against storage pest Tribolium castaneum (Coleoptera: Tenebrionidae)

Abstract

Fifty one Bacillus thuringiensis (Bt) like bacteria were isolated from diverse sources, viz. soil, silo dusts, insect cadaver, and phyllosphere and evaluated by feeding bioassays against larvae and adults of coleopteran pest red flour beetle, Tribolium castaneum (Herbst) in Division of Entomology, ICAR-IARI, New Delhi during 2014-15. It is a common pest known for attacking and infesting stored grains or products. Fifteen potential Bt strains were shortlisted on the basis of preliminary screening by single dose assays at 100 μg/g of diet against larvae and adults of T. castaneum. The virulence (LC50) of potential isolates was further assessed. The most effective Bt isolate was VKK-GJ4 (LC50=7.02 μg/g of diet) against neonates followed by VKK-GA6 (LC50=19.03 μg/g of diet) against adults of T. castaneum. Gene profiling of potential Bt strains revealed the presence of cry1, cry3, cry7, cry8, cry9, cry11, cry24 and cry28 gene. However, in three Bt strains, viz. JK-5, Tri5-5 and JKII3-2 no cry gene was found but they showed insecticidal activity against T. castaneum. Thus, quantification of the toxicity by insect bioassay is the only way to assess the potential of a strain for the pest control.