Baseline-susceptibility of the old-world bollworm, Helicoverpa armigera (Hubner) (Lepidoptera : Noctuidae) populations from India to Bacillus thuringiensis Cry1Ac insecticidal protein

The baseline-susceptibility of Indian populations of Helicoverpa armigera (Hubner) to the insecticidal protein Cry1Ac, from Bacillus thuringiensis (Berliner) was determined through bioassays conducted in 1999 and 2001. Populations of H. armigera were collected from cotton fields of nine major cotton growing states in India, which included (field locations in parentheses) Punjab (Bathinda), Haryana (Sirsa), Rajasthan (Sriganganagar), Madhya Pradesh (Barwah and Khandwa), Gujarat (Rajkot, Vadodra and Anand), Maharashtra (Jalgoan, Jalna, Akola and Yavatmal), Andhra Pradesh (Adilabad, Warangal, Khammam and Guntur), Karnataka (Raichur, Davangere and Ranebennur) and Tamil Nadu (Coimbatore and Dindigul). All populations were susceptible to Cry1Ac. The mean lethal concentrations, LC50-ranged from 0.14 to 0.71 and from 0.11 to 0.61; LC90 ranged from 1.17 to 6.94 and from 1.02 to 6.70 mug of Cry1Ac/ml of diet in 1999 and 2001 populations, respectively. Similarly, moult inhibitory concentrations, MIC50-ranged from 0.05 to 0.27 and from 0.05 to 0.14; MIC90-values ranged from 0.33 to 1.58 and from 0.25 to 0.91 mug of Cry1Ac in 1999 and 2001 populations, respectively. The effective concentrations (weight stunting related) EC50 ranged from 0.003 to 0.008 and from 0.0003 to 0.004; EC90 ranged from 0.029 to 0.076 and from 0.009 to 0.054 mug of Cry1Ac in 1999 and 2001 populations, respectively. These values form the baseline data for susceptibility of H. armigera to Cry1Ac and can be used as benchmarks for monitoring resistance to Cry1Ac. Bt cotton, expressing Cry1Ac, was approved for commercial cultivation in India in 2002. (C) 2003 Elsevier Ltd. All rights reserved.