Genetically modified (GM) cotton was developed to reduce the heavy reliance on pesticides. The bacterium Bacillus thuringiensis (Bt) naturally produces a chemical harmful only to a small fraction of insects, most notably the larvae of moths and butterflies, beetles, and flies, and harmless to other forms of life. The gene coding for Bt toxin has been inserted into cotton, causing cotton to produce this natural insecticide in its tissues. In many regions, the main pests in commercial cotton are lepidopteran larvae, which are killed by the Bt protein in the transgenic cotton they eat. This eliminates the need to use large amounts of broad-spectrum insecticides to kill lepidopteran pests (some of which have developed pyrethroid resistance). This spares natural insect predators in the farm ecology and further contributes to noninsecticide pest management.
Bt cotton is ineffective against many cotton pests, however, such as plant bugs, stink bugs, and aphids; depending on circumstances it may still be desirable to use insecticides against these. A 2006 study done by Cornell researchers, the Center for Chinese Agricultural Policy and the Chinese Academy of Science on Bt cotton farming in China found that after seven years these secondary pests that were normally controlled by pesticide had increased, necessitating the use of pesticides at similar levels to non-Bt cotton and causing less profit for farmers because of the extra expense of GM seeds.[23] However a more recent 2009 study by the Chinese Academy of Sciences, Stanford University and Rutgers University refutes this.[24] They concluded that the GM cotton effectively controlled bollworm. The secondary pests were mostly miridae (plant bugs) whose increase was related to local temperature and rainfall and only continued to increase in half the villages studied. Moreover, the increase in insecticide use for the control of these secondary insects was far smaller than the reduction in total insecticide use due to Bt cotton adoption. The International Service for the Acquisition of Agri-biotech Applications (ISAAA) said that, worldwide, GM cotton was planted on an area of 16 million hectares in 2009.[25] This was 49% of the worldwide total area planted in cotton. The U.S. cotton crop was 93% GM in 2010[26] and the Chinese cotton crop was 68% GM in 2009.[27]
The initial introduction of GM cotton proved to be a success in Australia – the yields were equivalent to the no transgenic varieties and the crop used much less pesticide to produce (85% reduction).[28] The subsequent introduction of a second variety of GM cotton led to increases in GM cotton production until 95% of the Australian cotton crop was GM in 2009.[25]
Cotton has mainly been genetically modified for resistance to glyphosate (marketed as Roundup in North America) a broad-spectrum herbicide sold by Monsanto, the same company that sells some of the Bt cotton seeds to farmers.[29] There are now a number of different cotton seed companies selling GE cotton around the world. Farmers buy new seed every year under a licensing agreement between the farmer and the company that has created the GE cotton.[citation needed]
GM cotton acreage in India continues to grow at a rapid rate, increasing from 50,000 hectares in 2002 to 8.4 million hectares in 2009. The total cotton area in India was 9.6 million hectares (the largest in the world or, about 35% of world cotton area), so GM cotton was grown on 87% of the cotton area in 2009.[27] This makes India the country with the largest area of GM cotton in the world, surpassing China (3.7 million hectares in 2009).
No comments:
Post a Comment