Mar 16, 2010
News
Genetically modified Bt cotton
Resistant pests found in India
Scientists working in the Indian state of Gujarat have discovered resistant pests in Bt cotton fields. Indian experts are now calling for more efficient measures to prevent or at least slow down a further spread of the resistance. So far, the only resistance to have emerged is resistance to the first generation of Bt cotton plants, which has been grown in India since 2002. Newer variants of Bt cotton have not yet been affected.
Bt cotton has found widespread acceptance in India: In 2009 it was grown on 8.4 million hectares. This equates to 89 per cent of India’s total cotton-growing area.
The pink bollworm (Pectinophora gossypiella) originates in Asia. Today it is found in all of the world’s cotton-growing regions.
Photos: ARS (top), Art Cushman, USDA; property of the Smithsonian Institution, Department of Entomology, Bugwood.org (above)
Scientists from the companies Mahyco and Monsanto, the manufacturer of Bollgard, the GM cotton in question, have found resistant pests in four districts of Gujarat. The pest in question is the pink bollworm. Bollgard cotton contains the Bt protein Cry1Ac to protect it against pests. So far, no resistant pests have been found in any of the other eight Indian states growing Bt cotton.
India has been carrying out field monitoring to check for the possible emergence of resistance among cotton pests since 2003. Following the discovery, monitoring is to be stepped up with the involvement of a network of experts led by India’s Central Institute of Cotton Research (CICR). Monsanto and Mahyco stress that the development of resistance is a natural phenomenon and that it was therefore to be expected.
The second generation of Bt cotton (Bollgard II) has evidently not yet been affected by resistant pests. Bollgard II has been grown in India since 2006 and contains not just one, but two different Bt proteins (Cry1Ac and Cry2Ab), which target the cotton bollworm and other pests. Pests are less likely to develop resistance to plants with several independent active insecticidal substances.
In 2009, Bollgard II was grown by 65 per cent of farmers in Gujarat. This figure is expected to rise to 90 per cent in 2010. Meanwhile, Monsanto is developing the third generation of Bt cotton, which will contain three different Bt proteins.
Researching the causes: refuge areas not big enough
The experts suspect that the emergence of resistant pests can be attributed to two causes. Firstly, they suspect that there were not enough refuge areas planted with conventional cotton varieties. Non-resistant pests can survive on these areas and keep down the numbers of resistant pests by breeding with them. Secondly, experts suspect that illegal cultivation of Bt cotton before it was officially approved by the Indian Genetic Engineering Approval Committee (GEAC) in 2002 could have played a part. It is possible that such plants would not have contained enough Bt protein, which would have encouraged the emergence of resistant pests.
Farmers are now to receive better training in collaboration with the CICR, which stresses the importance of suitable cultivation measures to prevent or at least slow down the spread of resistant pests. As well as sufficiently large refuge areas, these measures include deep ploughing, a diverse crop rotation and the removal of harvest residues, e.g. by grazing animals on the harvested fields.
In 2008, US scientist Bruce Tabashnik pointed out in a study that first signs of the emergence of pests resistant to the Cry1Ac protein had been found in Bt cotton in the USA. The first resistant cotton bollworms (Helicoverpa zea) developed in 2003 after seven years of cultivation. However, no other resistant pests have emerged so far. He recommended adapting resistance management measures, including growing Bt plants with two or more different Bt proteins, increasing the toxin concentrations in the plants and expanding the size of refuge areas.
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