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Refuge-in-bag (RIB) for Bt cotton

Refuge-in-bag (RIB) is an insect-resistance-management strategy in which non-Bt cotton seed is pre-blended into every commercial Bt cotton seed packet. The approach delays the evolution of Bt resistance in bollworm populations by ensuring that susceptible moths emerge alongside Bt-exposed populations, where they mate with any surviving resistant individuals and dilute the resistance alleles in the offspring.

Principle

Insect-resistance-management theory holds that the rate at which a pest develops resistance to a Bt toxin can be slowed by maintaining a "refuge" of non-Bt host plants. Susceptible insects emerging from the refuge mate with rare resistant survivors from the Bt crop; provided resistance is recessive, most offspring of such matings are heterozygous and still controlled by the Bt toxin.

Implementation

The Genetic Engineering Appraisal Committee (GEAC) initially mandated a structured perimeter refuge — typically five rows of non-Bt cotton or 20% of the sown area surrounding the Bt block — and bundled a separate 120 g non-Bt pack with each 450 g Bt pack. Compliance was poor: farmers frequently planted Bt seed across the entire field, including the area designated for refuge.

RIB replaces the structured refuge with a 5-10% blend of non-Bt seed mixed into every Bt seed packet, so refuge planting becomes automatic. The approach was endorsed in 2016 and rolled out commercially from 2020.

Adoption context

RIB is now the default for new Bt cotton seed packets sold in India. It complements other elements of the ICAR-CICR integrated package — timely sowing (Cotton Delayed Sowing Ipm), pheromone monitoring and field sanitation.

Limitations

Despite refuge policy, Pink Bollworm developed field resistance to Cry1Ac around 2009 and to the Bt Cotton Bg Ii (Cry1Ac+Cry2Ab) stack around 2015 — reflecting poor compliance under the original structured-refuge rule, intrinsic biology of the pest (limited adult dispersal, narrow host range, late-stage feeding within bolls that reduces exposure of susceptible moths to mating), and unequal performance of RIB blends in heterogeneous fields.

See also Bt Cotton Bg Ii, Pink Bollworm, Cotton Delayed Sowing Ipm.

References

  1. Refuge in bag for Bt cotton. Current Science.
  2. SWOT analysis of refuge-in-bag for Bt-cotton in India. ResearchGate.