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

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 (LC50) of Cry1Ac increased from a mean of 0.330 mu g mL(-1) (range 0.126-0.849 mu g mL(-1)) in 2013 to a mean of 6.938 mu g mL(-1) (range 3.52 to 10.30 mu g 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 LC50 value for Cry2Ab increased from a mean of 0.014 mu g mL(-1) (range 0.004-0.094 mu g mL(-1)) in 2013 to a mean of 12.51 mu g mL(-1) (range 3.92 to 28.10 mu g 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 LC50 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. (C) 2018 Society of Chemical Industry