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When it was introduced, in 2003, the Bt corn seemed to be the
answer to farmers' dreams. It was thought that it would allow
growers to bring in bountiful harvests using fewer chemicals
because the corn produces a toxin that poisons western corn
rootworms. The hybrid was such a swift success that it and
similar varieties now account for 65 per cent of all US corn acres
- producing grain that ends up in thousands of commonly consumed
foods, such as cereal, sweeteners and cooking oil.
However, in recent years, rootworms have feasted on the roots of
Bt corn in parts of four Midwestern states, suggesting that some of
the insects are becoming resistant to the crop's pest-fighting
powers. Scientists have suggested that this may be the result
of farmers planting Bt corn in the same fields year after year.
Most farmers rotate corn with other crops in a practice long
used to curb the spread of pests. But some farmers have
abandoned rotation because they need extra grain for livestock or
because they have grain contracts with ethanol producers.
Other farmers have eschewed the practice to cash in on high corn
prices.
Michael Gray, a science professor from the University of
Illinois, who is tracking Bt corn damage in that state says: 'Right
now, quite frankly, it's very profitable to grow corn.'
A scientist recently sounded an alarm throughout the biotech
industry when he published findings concluding that rootworms in a
handful of Bt cornfields in Iowa had evolved an ability to survive
the corn's defences. Similar crop damage has been seen in
parts of Illinois, Minnesota and Nebraska, but researchers are
still investigating whether rootworms capable of surviving the Bt
toxin were the cause.
Kenneth Ostlie, an entomologist at the University of Minnesota,
says the severity of the rootworm damage to Bt fields in Minnesota
had eased since the problem surfaced in 2009. Yet reports of
damage have become more widespread and he fears resistance could be
spreading undetected because the damage rootworms inflict often
isn't always apparent readily. Without strong winds, wet soil
or both, plants can be damaged at the roots but remain upright,
concealing the problem. He says the damage he observed in
Minnesota came to light only because storms in 2009 toppled corn
plants with damaged roots.
Ostlie says: 'The analogy I often use with growers is that we're
looking at an iceberg and all we see is the tip of the
problem. And it's a little bit like looking at an iceberg
through fog because the only time we know we have a problem is when
we get the right weather conditions.'
Seed producer, Monsanto, created the Bt strain by splicing a
gene from a common soil organism called Bacillus
thuringiensis into the plant. The natural insecticide it
makes is considered harmless to humans and livestock.
Scientists always expected rootworms to develop some resistance to
the toxin produced by the gene. But the worrisome signs of
possible resistance have emerged sooner than many expected.
The US Environmental Protection Agency (EPA) recently chided
Monsanto, declaring in a report released on 22 November 2011 that
it wasn't doing enough to monitor suspected resistance among
rootworm populations. The report urged for a tougher
approach, including expanding monitoring efforts to a total of
seven states, including Colorado, South Dakota and Wisconsin.
The EPA also wanted to ensure farmers in areas of concern begin
using insecticides and other methods to combat possible
resistance.
Monsanto insists there's no conclusive proof that rootworms have
become immune to the crop, but the company says it regards the
situation seriously and has been taking steps that are 'directly in
line' with federal recommendations.
Some scientists fear it could already be too late to prevent the
rise of resistance, in large part because of the way some farmers
have been planting the crop. They point to two factors:
farmers who have abandoned crop rotation and others who have
neglected to plant non-Bt corn within Bt fields or in surrounding
fields as a way to create a 'refuge' for non-resistant rootworms in
the hope that they will breed with resistant rootworms and dilute
their genes.
Experts worry that the actions of a few farmers could jeopardise
an innovation that has reduced pesticide use significantly and
saved growers billions of dollars in lost yields and
chemical-control costs.
Biotechnology director at the Center for Science and Public
Policy, Gregory Jaffe, says: 'This is a public good that should be
protected for future generations and not squandered too
quickly.'
Iowa State University entomologist, Aaron Gassmann, published
research in July 2011 concluding that resistance had arisen among
rootworms he collected in four Iowa fields. Those fields had
been planted continuously for three to six years with Bt corn - a
practice that ensured that any resistant rootworms could lay their
eggs in an area that would offer plenty of food for the next
generation.
For now, the rootworm resistance in Iowa appears isolated, but
Gassmann says that could change if farmers don't take action
quickly. The rootworm larvae grow into adult beetles that can
fly, meaning resistant beetles could easily spread to new areas.
Gassmann concludes: 'I think this provides an important early
warning.'
Besides rotating crops, farmers can also fight resistance by
switching between Bt corn varieties, which produce different
toxins, or by planting newer varieties with multiple toxins.
They can also treat damaged fields with insecticides to kill any
resistant rootworms, or employ a combination of all those
approaches.
The EPA requires growers to devote 20 per cent of their fields
to non-Bt corn. After the crop was released in 2003, nine out
of ten farmers met that standard. Now it is only seven or
eight says Jaffe.
Seed companies are supposed to cut off farmers with a record of
violating the planting rules, which are specified in seed
purchasing contracts. To improve compliance, companies are
now introducing blends that have conventional seed premixed with Bt
seed.
Brian Schaumburg, who farms 1,400 acres near the north central
Illinois town of Chenoa, plants as much Bt corn as he can every
spring. But he says that he shifts his planting strategy each
year, varying which Bt corn hybrids he uses and applying pesticides
when required, to reduce the chances of rootworm resistance
emerging in his fields. He says he always plants the required
refuge fields and believes very few farmers defy the rule. He
believes those who do, put the valuable crop at risk. 'If we don't
do it right, we could lose these good tools,' he says.
If rootworms do become resistant to Bt corn it, 'could become
the most economically damaging example of insect resistance to a
genetically modified crop in the US,' concludes Bruce Tabashnik, an
entomologist at the University of Arizona. 'It's a pest of
great economic significance - a billion dollar pest.'
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