Abstract
Bt cotton expressing Cry1Ac insecticidal protein was introduced in India in 2002. Within a span of 12 years, Bt-cotton constituted more than 90% of cropping area covering 11.6 mHa. This large scale cultivation favours resistance evolution in target pests. One of the major factors that influences rate of resistance is frequency of resistance alleles. Using F2 screen methodology and a discriminating dose, we estimated the level of resistance to Cry1Ac toxin in field populations of Helicoverpa armigera (Hübner). We report an increase in Cry1Ac resistance allele frequency in field populations of H. armigera collected in Telangana and Andhra Pradesh states of India. Collective allele frequency was 0.085 (95% CI) for 2013 and 0.035 (95% CI) for 2014, which was 65 times and 29 times higher than the initial frequencies estimated during 2004. To prevent further increase in Bt resistance frequency in H. armigera, it is necessary to integrate other resistance management tactics that preserves pest susceptibility to Bt cotton.
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