High levels of Bt cry toxin resistant allele frequency in South Indian populations of cotton pink bollworm, Pectinophora gossypiella Saunders (Gelechiidae: Lepidoptera)

The lack of compliance with refugia planting by growers of transgenic cotton expressing toxins from Bacillus thuringiensis (Bt) is a major factor contributing to the development of resistance to Bt toxins Cry1Ac and Cry2Ab and outbreak of pink bollworm, Pectinophora gossypiella in several cotton growing regions of India. The present study estimated the resistant alleles frequency in South Indian populations of P. gossypiella against Cry1Ac + Cry2Ab toxins produced by Bt Bollgard II® cotton. Among the 33 established isofemale families, 19 laid fertile eggs and reached the F₁ generation, of which 10 survived the F₂ screen. Further, individuals from four isofemale families survived the reconfirmation test at the F₃ generation, which was conducted to eliminate false-positive lines for the resistance. These four families are the true positives for carrying Cry toxin resistance alleles. The frequency of Cry toxin resistance alleles was estimated at 0.059, indicating a relatively high prevalence of individuals carrying resistant alleles for both Cry1Ac and Cry2Ab toxins. The present study affirms the existence of a high frequency of resistance alleles in individuals of P. gossypiella populations collected from South India. The outbreak-like situation of P. gossypiella in cotton fields underscores the urgent need for developing and implementing alternative technologies within an Integrated Pest Management (IPM) framework. The present estimates provide valuable baseline data for monitoring resistance alleles frequency in pink bollworm populations.