Mass release of susceptible males dilutes Bollgard II® Bt resistance in pink bollworm: A semi-field validated strategy

The pink bollworm, Pectinophora gossypiella (Lepidoptera: Gelechiidae), poses a significant threat to Bt cotton cultivation in India due to field-level resistance against Cry1Ac and Cry2Ab toxins. Existing pest management tactics have proven inadequate. To address this, homozygous susceptible (RR) male moths were mass-reared in the laboratory and released into Bt Bollgard II® cotton fields. Success was enhanced by trapping and removing feral resistant males with pheromone traps prior to releasing susceptible males. The effectiveness was assessed using bioassays, resistance dilution genetics, fitness cost estimation, field validation, and gene expression analysis. Resistance dilution was evident in both laboratory back-cross progenies and field progenies from feral females mated with released susceptible males. Resistance was autosomal with recessive inheritance for both Cry toxins. In treated plots, boll damage and larval numbers were significantly reduced. Genes linked to Bt resistance, including PgCad1, PgABCA2, APN, and ABCG8, showed significant down regulation (−4.93, −2.63, −1.73, and −1.49 fold, respectively), indicating partial restoration of susceptibility in field-collected larvae following mating (Field-R ♀ × Lab-S ♂). These findings highlight the potential of mass-releasing susceptible males as an effective and sustainable strategy for managing Bt-resistant pink bollworm, providing an alternative to traditional insecticide-based approaches.