Since 2002, transgenic crops that produce Cry1Ac and Cry2Ab toxins have been used in India to control bollworms. From 2002 to 2009, Bt-cotton effectively controlled the pink bollworm (PBW). However, since 2009 numerous studies have reported high survival of PBW on Bt-cotton expressing Cry1Ac and Cry2Ab toxins, indicating reduced susceptibility to Cry toxins expressed in Bt-cotton. In the current study, we attempted to estimate the frequency of resistance alleles to Cry1Ac and Cry2Ab toxins in a field collected population of pink bollworms from Andhra Pradesh. Resistance allele frequency was estimated using an F 2 screen methodology for the first time after 17 years of Bt-cotton cultivation. Our study finds that the allele frequency for Cry1Ac is 0.082 and for Cry2Ab is 0.054, with a detection probability of greater than 97%. In our survey conducted in 2018-19 and 2019-20, we also noticed high survival and damage by PBW on Bt-cotton expressing Cry1Ac and Cry2Ab. Our survey report reveals, > 30% flower damage, > 90% green boll damage and > 80% locule damage by PBW on Bt-cotton expressing Cry1Ac and Cry2Ab toxins.
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