Relative Response of Pink Bollworm, Pectinophora gossypiella (Saunders) Population Towards Bollgard-II® Bt Cotton Expressing Cry1Ac+Cry2Ab Toxins.

The widespread adoption of genetically modified (GM) crops, particularly Bt cotton expressing Cry1Ac and Cry2Ab toxins, has revolutionized global agriculture by providing effective solutions to pest-related challenges. However, the Pink Bollworm, Pectinophora gossypiella, a highly destructive insect pest threatening cotton cultivation worldwide, has developed resistance to Bt cotton, leading to reduced benefits. This study aimed to assess the relative response of Pink Bollworm population collected from different regions in South India to Bollgard-II® Bt cotton expressing both Cry1Ac and Cry2Ab toxins. Field populations of Pink Bollworm were collected from major cotton-growing areas in Karnataka (Raichur, Dharwad and Yadgir), Tamil Nadu (Jolarpet) and Gujarat (Vadodara), while a laboratory-susceptible population served as a reference. The results showed that pink bollworm populations from various locations exhibited different levels of resistance to Bollgard-II® Bt cotton. Median lethal concentration (LC₅₀) values for field populations ranged from 0.790 to 1.011 ppm, indicating reduced susceptibility compared to the susceptible laboratory colony (LC₅₀ = 0.011; χ² = 0.829; df = 3; h = 0.414). The highest resistance ratio (RR) of 91.90 was recorded in the population collected from Vadodara (LC50= 1.011; χ² = 2.461; df=3; h= 0.820), followed by Raichur (RR = 90.63; LC50 = 0.997; χ² = 7.523; df = 3; h = 2.509), Yadgir (RR = 89.63; LC₅₀ = 0.986; χ² = 3.862; df =3; h = 1.288) and Dharwad (RR = 84.64; LC₅₀ = 0.931; χ² = 5.334; df =3; h = 1.781). The population collected from Jolarpet (LC₅₀ = 0.790; χ² = 3.815; df = 3; h = 1.272) showed resistance ratio of 71.81, lowest among the populations tested. These findings highlight the increased resistance of pink bollworm to the combined Cry1Ac and Cry2Ab toxins in Bollgard-II® Bt cotton, indicating the need for careful management strategies to delay further resistance development. These results emphasize the importance of sustainable agricultural practices to overcome the challenges posed by insect pests in GM crop cultivation. [ABSTRACT FROM AUTHOR]