Field‐evolved resistance of pink bollworm, Pectinophora gossypiella (Saunders) (Lepidoptera: Gelechiidae), to transgenic Bacillus thuringiensis ( Bt ) cotton expressing crystal 1Ac (Cry1Ac) and Cry2Ab in India

Abstract BACKGROUND Pink bollworm (PBW) adaptation to transgenic Bacillus thuringiensis ( Bt ) cotton expressing crystal 1Ac (Cry1Ac) ( Bt ‐I) and Cry1Ac + Cry2Ab ( Bt ‐II) was assessed in India during 2010–2017 in 38 districts of the 10 major cotton‐growing states. RESULTS PBW larval incidence on Bt cotton was nil in northern India, wherein the resistance ratios (RRs) to Cry1Ac were 26–262 and those to Cry2Ab were 1–108. In central and southern India, the annual average PBW larval recovery from Bt II cotton was high at 28.85–72.49% during 2014–2017. In central and southern India, the 50% lethal concentration (LC 50 ) of Cry1Ac increased from a mean of 0.330 µg mL −1 (range 0.126–0.849 µg mL −1 ) in 2013 to a mean of 6.938 µg mL −1 (range 3.52 to 10.30 µg mL −1 ) in 2017 and the RR increased from a mean of 47.12 (range 18–121) in 2013 to a mean of 1387 (704–2060) in 2017, whereas the LC 50 value for Cry2Ab increased from a mean of 0.014 µg mL −1 (range 0.004–0.094 µg mL −1 ) in 2013 to a mean of 12.51 µg mL −1 (range 3.92 to 28.10 µg mL −1 ) in 2017 and the RR increased from a mean of 5.4 (range 1–31) in 2013 to a mean of 4196 (1306–9366) in 2017. CONCLUSION High PBW larval recovery on Bt ‐II in conjunction with high LC 50 values for Cry1Ac and Cry2Ab in major cotton‐growing districts of central and southern India provides evidence of field‐evolved resistance in PBW to Bt ‐I and Bt ‐II cotton. © 2018 Society of Chemical Industry