The Minister of State for Agriculture, Dr. Akhilesh Prasad Singh informed, in reply to a question in Rajya Sabha today that, the study conducted by Central Institute for Cotton Research (CICR) showed that the American bollworm will develop resistance to Bt-cotton after a few years depending mainly on the extent of area under Bt-cotton in the country.  With the current rate of increase in the area under Bt-cotton, it is likely to take about 11-12 years for the pest to develop resistance to Bt-cotton.  However, with implementation of proper strategies as suggested by CICR, it is possible to delay resistance by at least 30-40 year, if not more.

A stochastic model ‘Bt-Adapt’ was developed to simulate the rate of resistance development of H. armigera to Cry1Ac under Indian farming conditions.  The model integrates genetic and ecological parameters of H. armigera in relation to its response to the Cry1Ac expressing Bt cotton. The model can predict the time that would take for bollworm to develop resistance in different cotton-growing districts of the country based on the input statistics of area under Bt-cotton in each of the districts, or even the proposed area to be cultivated under Bt cotton.

Simulation analysis showed that relative survival rate of the Cry1 Ac resistant homozygous (RR), heterozygous (RS) and homozygous susceptible (SS) H. armigera genotypes on Bt cotton, was the most important factor influencing resistance development.  In the order of significance, the other factors that had the greatest impact on resistance development were, the relative proportion of area under Bt cotton, dominance of the resistant allele and initial frequency of resistant alleles in field populations.  The extent of population reduction in Bt cotton and non-Bt crops due to pest control, was found to have a significant impact on the rate of resistance development.

The Indian Council of Agricultural Research (ICAR) has initiated a net-working project in 2004, to carefully monitor resistance development in all the 9 cotton growing states of the country and also to scientifically analyze all factors that contribute to resistance development.  The national net-working group has been given the task of developing resistance management strategies from time to time every year and disseminate them to all the stakeholders, including the Genetic Engineering Approval Committee (GEAC), the state agricultural Universities, Government institutions, farmers, Non-Governmental Organisation (NGO), etc.

Based on the simulation analysis, using the ‘Bt-Adapt’ model, and scientific data available so for, CICR has proposed some important resistance management strategies to the GEAC.  The strategies place emphasis on reducing populations of H. armigera that survive Bt cotton and enhancement of area of alternate host crops that are as attractive as cotton to H. armigera, to be used as trap crop or intercrop refuges.  If proper pest management measures are followed to ensure that at least 90 per cent of the surviving larvae of the American bollworms in Bt-cotton fields, are killed with biopesticides, resistance can be delayed to 45 years even with 40 per cent area under Bt cotton. 

The strategies, that would enable extending the usefulness of Bt technology would be:

• Use eco-friendly methods such as cultural control or hand-picking of surviving bollworms in Bt cotton fields.  Deep-ploughing of fields immediately after Bt-cotton harvest to destroy resistant pupae.

• Biopesticides that are neem based or HaNPV (virus) were found to be more effective on larvae surviving on Bt-cotton because of their slower growth as compared to those on the conventional non-Bt cotton.  Hence these would be useful to manage younger larvae on 60-90 days old crop.  Alternatively, eco-friendly insecticides such as spinosad, emamectin benzoate, novaluron or Indoxacarb can be used on 90 and 120 days old crop to reduce populations of resistant insect genotypes. 

• Use of attractive synchronous alternate host crops such as marigold, sunflower, chillies etc. for H. armigera which could be used as intercrop or trap crop refuges.

• Use alternate genes that do not share common resistance mechanisms as that of Cry1Ac, in transgenic plants either in rotation or alternation or mixtures such as the dual-gene based Bt-cotton varieties.