Genetically modified corn, which produces anti-pest toxin, is no longer as efficient at killing the bugs. The resistance arose quickly, due to some extent, to farmers avoiding the simple, but profit-cutting precaution of crop rotation.
The problem that may soon render null the economic and
environmental benefits of GM maize, which produces the so-called
Bacillus thurinigiensis (Bt) toxin, was highlighted in a study
published online in this week’s Proceedings of the National
Academy of Sciences.
In the paper, a team led by Aaron Gassmann, an entomologist
at Iowa State University in Ames, described the rise in some Iowa
fields of a bug called the western corn rootworm (Diabrotica
virgifera virgifera).
The studied pest has developed resistance to two of three types
of Bt toxins currently available on the market.
The vulnerability of GM corn could lead to disastrous
consequences for farmers and the environment, Gassmann warned.
“Unless management practices change, it’s only going to get
worse,” he said. “There needs to be a fundamental change
in how the technology is used.”
The US authorized use of Bt toxin-producing corn back in 2003.
Since then the GM plants, which were believed not to require
implementation of insecticides to combat rootworms and other
pests, has dominated the market and currently accounts for
three-quarters of the American corn crop.
However, the first cases of rootworm damage to GM plants were
registered in 2009, with corn containing Cry3Bb1 Bt toxin being
affected.
Two years later, the bugs started attacking the fields, at which
the second toxin – mCry3A – was used by the farmers.
The lab tests performed by Gassmann and his team have revealed
that a case of cross-resistance is in place as the pests that had
become resistant to Cry3Bb1 were also resistant to mCry3A.
The most likely explanation to the phenomenon is that both toxins
share structural similarities and some binding sites in the
insect’s gut, the paper said.
According to the research, the Bt corn simply doesn’t produce
enough toxin to fully control the rootworms, who are known as
really tough creatures.
Unlike the majority of other pests, which are almost completely
defenseless against the toxins, over 2 percent of the rootworms
can survive contact with Bt maize.
Resistance in the worms can develop very fast in fields where the
same kind of maize is being grown every year. In Iowa, it showed
up after an average of 3.6 years, the paper warns.
Agricultural biotechnology companies currently apply the
so-called ‘pyramiding’ technology to their seeds so that they can
produce two different Bt toxins, with one of them being
Cry34/35Ab1 that so far has not seen any resistance developed by
the rootworms.
Gassmann confirmed that the pyramiding of toxins is an important
way to delay the development of resistance, but added that the
combination becomes less effective once resistance arises to one
of the toxins.
So, while relying on technology, the farmers shouldn’t forget
about such old-fashioned practices as crops rotation as it helps
disrupt the pests life cycle.
“The rootworm can’t survive if the corn’s not there,” he
explained.