Acreage under Bt cotton, an insect-protected hybrid from Mahyco Monsanto Biotech (MMB), has witnessed a sharp increase for the past three years across nine cotton growing states in India.Cotton farmers planted Bollgard and Bollgard II, across 3.1 million acre in 2005, grew to 8.7 million acre in 2006, and increased to 14.4 milion acre in 2007, a company release said.As far as Tamil Nadu was concerned, Bollgard cotton acreage has increased by 29% to 2.85 lakh acre in 2007 from 2.2 lakh acres in 2006, MMB said.By adopting MMB's Bollgard technology, farmers engaged in cotton cultivation in South India - Karnataka, Andhra Pradesh and Tamil Nadu - had earned Rs 825 crore as additional income in 2006, the release said.Overall, farmers in all nine Bt cotton growing sstates had earned Rs 7,039 crore as additional income in 2006, based on 8.7 million acreage penetration achieved during the crop season, MMB, quoting a nation-wide survey on 'Economic benefits of BT cotton cultivation in India,' said.