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Bt resistance a threat to organic farmers

A study shows that boll weevils have evolved to resist Bt cotton, a genetically modified crop that contains a soil bacterium usually deadly to pests. But just what is Bt and what are its implications for organic agriculture?

A new study entitled "Insect resistance to Bt crops: evidence versus theory," and published in the February 2008 issue of Nature Biotechnology has discovered boll weevils with field-evolved resistance to Bt cotton. Bt cotton is genetically modified to contain Bacillus thuringeinsus, a naturally occurring soil bacterium deadly to many pests, including a variety of larval moths that prey on cotton bolls.

Bt-resistant bollworms were found in fields in both Mississippi and Arkansas in 2003 and 2006, according to lead researcher Bruce Tabashnik. "What we're seeing is evolution in action," Tabashnik said.

"This sets the countdown clock ticking for generic pest resistance to Bt," said Bob Scowcroft, executive director of the Organic Farming Research Foundation, based in Santa Cruz, Calif. "Our questions from day one were about how long it would take for pests to become resistant. The answer from Monsanto was that it didn't matter, because they'd just engineer a new gene into [Bt cotton]."

Indeed, Monsanto has now introduced Bollgard II, a two-gene product, and is urging all farmers to begin the transition to the new product, which is intended to be complete by the 2010 planting season. Monsanto argues on its website that "the two-gene product should have an exponentially longer life than the single trait, as it is virtually impossible to develop simultaneous resistance to two different modes of action."

What is Bt and how does it affect organic?

New versions of Monsanto's patented cotton may continue to be effective. But general pest resistance to the insecticidal crystal proteins found in Bt may mean that Bt field applications will be increasingly ineffective against an increasing variety of pests. "In organic farming, Bt is a special tool to use under extreme circumstances," Scowcroft said. "Having it taken out of your organic toolbox means you have almost no other options to control the specific targeted pest Bt is assigned to be used against."

That is exactly what the organic agriculture community feared when Monsanto first introduced Bt cotton in 1996. Supporters argued that the new product was an environmental blessing because it would dramatically reduce the amount of pesticide sprayed on cotton, a notoriously pesticide-intensive crop. Opponents said that the crop would inevitably cause widespread Bt resistance.

Bt-resistant bollworms have thus far been discovered only in the United States, where farmers are required to plant non-Bt crops nearby to help slow the development of resistance. With the widespread use of Bt cotton in countries like India and China, where such methods are not required, bollworm resistance may already be a global phenomenon.

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