Potential of Native Bacillus thuringiensis Strains against Cotton Aphid, Aphis gossypii Glover

Abstract

Results on the evaluation of three native strains of Bacillus thuringiensis isolated from silo dust along with reference strains i.e. Bt var. Kurstaki (Btk) and Bt var. israelensis (Bti) for insecticidal activity against the cotton aphid, Aphis gossypii are reported. The feeding assays were carried out against adults in three different forms viz., pre-solubilized form (spore + crystal), solubilized form (pre-toxin form) and trypsinized form (toxin form) by diet incorporation method. Among the reference strains, Btk HD-1 showed maximum mortality (80%) in trypsinized form. Bti was effective in both pre-solubilized (66.6% mortality) and trypsinized form (70% mortality). The native Bt strains VKK-GA1, VKK-GA6 and VKK-GJ4 were found effective in both solubilized and trypsinized form (mortality 50–80%), while nominal efficacy (13.3–30% mortality) was observed in pre-solubilized form. Gene profiling of native strain showed the presence of cry1 and 9 in VKK-GA6, cry7 in VKK-GA1 and novel amplicon of cry9 in VKK-GJ4. The present study revealed the efficacy of Cry7 and Cry9 toxins against cotton aphid. This may be the first report in this context.