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Pink bollworm Bt-resistance crisis in Indian cotton Photo: Shree_clips B · Pexels License · source ↗

Pink bollworm Bt-resistance crisis in Indian cotton

The development of field resistance in pink bollworm (Pectinophora gossypiella) to the Cry1Ac and Cry2Ab proteins expressed by Bollgard-II (Bt Cotton Bg Ii) is the single largest crisis facing Indian cotton since Bt commercialisation. The collapse of transgenic protection against this pest has reset the economics of cotton cultivation across the central and southern zones.

Timeline

  • 2002: Bollgard-I (Cry1Ac alone) approved for commercial cultivation.
  • 2006: Bollgard-II (Cry1Ac + Cry2Ab stack) approved.
  • 2009: First confirmed field resistance to Cry1Ac in pink bollworm in Gujarat.
  • 2014-15: Confirmed resistance to the Cry1Ac+Cry2Ab BG-II stack — Vidarbha and Marathwada regions.
  • 2017-18: Devastating BG-II failures in Maharashtra — 30-40% boll damage reported on adopted fields; state government compensation invoked.
  • 2020 onwards: Resistance broadly established across central and south zones; population dynamics now resemble pre-Bt era.

Mechanism of failure

Resistance arose through (a) widespread non-compliance with refuge planting (Refuge In Bag Cotton) — farmers ignored or replaced refuge seed; (b) extended cropping windows that gave pink bollworm overlapping generations on the same field; (c) absence of trait rotation as BG-II was the only available stacked event; and (d) sub-lethal Cry expression in late-season bolls.

Consequences

ICAR-CICR data document yield losses of 20-40% on unmanaged BG-II crop. Insecticide use against bollworm — which had dropped sharply after 2002 — has rebounded to pre-Bt levels in affected districts. Per-acre cost of cultivation has risen; smallholder vulnerability to crop failure has increased; cotton acreage in Vidarbha and Marathwada has declined as farmers shift to soybean, pigeon pea or maize.

Management response

ICAR-CICR's pink-bollworm-management package combines (a) timely sowing within the recommended window with hard crop termination by December (Cotton Delayed Sowing Ipm); (b) pheromone-trap monitoring with mass trapping at 8 traps/ha; (c) inundative Trichogramma bactrae and T. brasiliensis releases; (d) ETL-based insecticide sprays (chlorantraniliprole, emamectin benzoate, spinetoram); (e) destruction of crop residue and stubble. Demonstration plots achieved 33-43% reduction in infestation versus farmer practice.

Future trait pipeline

Vip3A-based Bollgard-III (Cotton Bg Iii Roundup Flex Regulatory) is the most advanced replacement trait but remains unapproved. CICR is exploring RNAi-based gene-silencing constructs and pyramided Vip3+Cry stacks but none has reached commercial pipeline.

See also Pink Bollworm, Bt Cotton Bg Ii, Refuge In Bag Cotton, Cotton Delayed Sowing Ipm, Cotton Bg Iii Roundup Flex Regulatory.

Sources

  1. Entomology research on pink bollworm. ICAR-CICR Nagpur.
  2. Resistance development in pink bollworm against Bt cotton. Scientific Reports.
  3. Why pink bollworm is eating up Bt cotton. Down to Earth.