Frequency of alleles conferring resistance to Cry1Ac toxin of <em>Bacillus thuringiensis</em> in population of <em>Helicoverpa armigera </em> (Hübner)<em> </em> (Lepidoptera: Noctuidae) from India

Abstract

Detection of major resistance allele may have greater implication in resistance management. A field collected population of the cotton bollworm <em>Helicoverpa armigera</em> (Hübner) was used to test F₂ screening developed for monitoring the development of resistant alleles to Cry1Ac toxin of <em>Bacillus thuringiensis.</em> From four different locations <em>viz</em>., Bangalore, Dharwad, Raichur and New Delhi (IARI), <em>H</em>.<em> armigera</em> was collected and 146 isofemale lines were prepared from the field collected population. Out of which, 42 isofemale lines were used for F₂ screening of Cry1Ac resistant alleles using diet incorporation method. Other 65 isofemale lines were also prepared separately, for screening susceptibility in order to estimate fold resistance. In the F₂ screening, four positive lines were obtained. The fold resistance was observed to be 231.33. The F₂ screening results showed that the expected <em>Bt</em> resistance allele frequency in the collected populations was 0.085 with 95% confidence interval of 0.009 to 0.256 indicating that the F₂ screening method can be used to detect major alleles conferring resistance to <em>Bt</em> cotton in insect.