INCIDENCE OF THE PINK BOLLWORM, Pectinophora gossypiella (SAUN.) ON Bt COTTON AND STUDIES ON THE STRATEGIES FOR RESISTANCE MANAGEM
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Date
2020-05-29
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UNIVERSITY OF AGRICULTURAL SCIENCES, GKVK BENGALURU
Abstract
Studies on the incidence of the pink bollworm (PBW) on Bt cotton and strategies
for resistance management, was carried at Department of Entomology, UAS, GKVK,
Bangalore during 2015-19. Damage caused by PBW to Bt cotton plants and relating the
extent of damage with the presence/absence of cry genes in the plants was assessed at three
cotton-growing regions. The damage assessment was done at plant, boll and locule levels
in each selected field. The results showed no distinct pattern in the infestation pattern
across space and time. The Bt cotton plants producing both Cry1Ac and Cry2Ab toxins
were as much damaged by PBW as those producing either one, or none, of the toxins.
Segregation pattern of BG-II hybrids suggested that Bt toxins in the F2 generation
segregated according to Mendelian mono and di-hybrid ratios. This exposes the PBW
populations to seeds with, both, any one or none of the Bt toxins. Further, seeds with
different genes within a boll exposes a PBW individual to a variety of toxin-containing
seeds. This appears to be a strong reason for the development of resistance in PBW. To
enforce refuge compliance, the Government of India allowed mixing of 5 to 10% non-Bt
seeds in every Bt seed bag (Refuge-in-Bag) with a minimum trait purity of 90%. Our study
revealed that 5% of non-Bt seeds were already present in the seed bags before the
implementation of the RIB strategy. Direct and indirect evidences suggested that the PBW
larvae moved between bolls that were available in the overlapping canopies of adjacent
cotton plants. Larval movement across the canopy of Bt and non-Bt plants under the RIB