Response of pink bollworm Pectinophora gossypiella (Saunders) to Cry1Ac and Cry2Ab toxin

BackgroundDuring field surveillance in Gujarat, India, in 2009, scientists found that pink bollworm was surviving in the first generation of Bollgard cotton, which contains a single protein. This survival was observed in four districts of Gujarat. From 2012 to 2014, surveys revealed that pink bollworm larvae had higher survival rates on Bollgard II cotton in Amreli and Bhavnagar districts. In 2016, a pink bollworm outbreak in Maharashtra caused significant losses in cotton production, leading to damage, yield losses, and increased management costs in several regions. The objective of the present study was to determine the reaction of Pectinophora gossypiella to Cry1Ac and Cry2Ab toxins.ResultsNeonates of P. gossypiella collected from six distinct locations in Vidarbha were subjected to seven different concentrations of Cry1Ac. The highest LC50 value was recorded in the population collection of Yavatmal (1.362 mu g/ml diet) but the lowest LC50 value of 0.600 mu g/ml diet in Buldana population. The highest MIC50 value was recorded in the population collected from Yavatmal (0.743 mu g/ml diet) and the lowest MIC50 value of 0.413 mu g/ml diet in the Buldana population (0.431 mu g/ml diet). The highest IC50 value was recorded in the population collected from Yavatmal (0.303 mu g/ml diet) but the lowest IC50 value of 0.127 mu g/ml diet in the Buldana population. Neonates of P. gossypiella collected from six different locations in Vidarbha were exposed to seven different concentrations (9.0, 3.0, 1.0, 0.333, 0.111, 0.037 and 0.012 for Cry1Ac and 27.0, 9.0, 3.0, 1.0, 0.333, 0.111 and 0.037 mu g/ml for Cry2Ab) which revealed that the Yavatmal population had the highest LC50 value of 94.294 mu g/ml diet and the lowest LC50 value was recorded in the Amravati population (42.144 mu g/ml diet). The highest MIC50 value of 27.258 mu g/ml diet was recorded in Buldana population, but the lowest MIC50 value was recorded in the Amravati population (12.881 mu g/ml diet). The highest IC50 value of 3.209 mu g/ml diet was observed in Yavatmal population, and the lowest one was recorded in the Amravati population (1.574 mu g/ml diet).ConclusionsAccording to the LC50 values, all of the P. gossypiella populations in Vidarbha were extremely insensitive and had field-evolved resistance to the Bt proteins found in the transgenic cotton varieties of Bollgard II.