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January, 2008
Already a widespread pest on
American maize fields, the western corn rootworm has recently
been on the move, making its way to cropland throughout Europe.
In 2003, the US approved MON 863, a genetically modified maize
line that produces a substance making it resistant to the corn
rootworm.
Source:
GMO Compass
In January 2006, the EU followed
suit by granting authorisation for MON 863 for food and feed.
Some experts believe MON 863 maize would be a good solution to
the increasing western corn rootworm problem in Europe. The
approval process, however, has sparked disagreement between
European authorities, environmental groups, and Monsanto, the
company responsible for developing the resistant cultivar.
Nonetheless, the European Food Safety Authority (EFSA) came to
the decision that the genetically modified maize is as safe as
conventional maize.
A
dreaded pest
The
western corn rootworm (Diabrotica virgifera) is a major
problem for American maize growers. Rootworm larvae begin their
lives in the soil and emerge to chew the aerial roots of maize
stalks. Later in life, the larvae penetrate these damaged roots
and gain access to the inner stalk. The root damage caused by
larval entry makes maize stalks prone to tipping before harvest,
which in severe cases can destroy 80 percent of the crop. In
addition, the damaged roots can serve as points of entry for
secondary infections. Adult beetles emerge in the summer between
July and September and survive until the onset of frost. They
feed on above-ground plant parts, especially on pollen and silk.
During heavy infestations, damage to maize silk can reduce
fertilisation efficiency resulting in fewer and smaller kernels.
Traditionally, the pest has been combated with intensive
insecticide applications. The price tag on the western corn
rootworm including spraying costs and yield losses comes up to 1
billion US dollars annually, hence the pest’s nickname, the
billion dollar bug. If the pest becomes widespread in Europe,
costs are projected at half a billion euro.
Transatlantic flight
The western
corn rootworm is native to Central America, but in recent
decades it has made itself a new home in maize growing regions
of North America. Sprawling maize monocultures made a perfect
environment for the explosive spread of the rootworm across the
continent. Although the pest was unknown in Europe until the
1980s, European farmers can no longer expect to be spared.
Thanks to
modern mass-transportation, the western corn rootworm has
managed to secure a foothold in Europe. Since the early
nineties, the pest has been turning up on European soil,
primarily in the vicinity of airports. The beetles may be lured
into the illuminated cargo holds of airplanes or may just happen
to fly into passenger cabins. In any case, the pest seems to
have no trouble surviving a transatlantic voyage.
The western
corn rootworm was first reported in Europe near Belgrade’s
airport in 1992, and it subsequently extended its presence
across parts of Eastern Europe. The pest can spread up to 100
kilometres per year in regions of intensive maize cultivation.
In the
following years, the rootworm appears to have reached Europe on
other transatlantic flights. The beetle was found near Venice’s
airport in 1998, near a loading station in Lombardy, Italy in
2000, in Paris in 2002, and in Belgium, the Netherlands, and
Great Britain in 2003. In the fall of 2003, beetles were
discovered in the Alsace/Basel-Mulhouse region near the borders
of France, Switzerland, and Germany.
In response
to the appearance of beetles in the Basel-Mulhouse region,
authorities implemented containment measures. Approximately 100
hectares of maize were destroyed, and the rest of the maize in
the affected region was treated with insecticide.
As early as
1997, German authorities have made pre-emptive efforts to
promptly detect the potential appearance of the western corn
rootworm and to develop appropriate containment strategies.
Five years
after the pest’s first appearance in Europe, losses are already
becoming visible. Areas of Europe with intensive maize
cultivation can expect to see the presence of the rootworm
spread extremely rapidly. Because the beetle over-winters in
maize roots, regions where maize is planted on the same field
year after year are particularly susceptible.
Is there a way to stop the
spread of the western corn rootworm?
In October
2003, the European Commission agreed on a set of measures in
order to stop, or at least slow down the spread of the western
corn rootworm.
To detect
the pest as early as possible, traps were set up and baited with
pheromones to attract female beetles. Each year, the findings of
the trapping studies are submitted to the European Commission.
Should the western corn rootworm be found, it must be reported
immediately. A one kilometre radius surrounding the site of
incidence is declared a zone of infestation, and a five
kilometre radius is declared a security zone.
The primary
control measure within these zones is crop rotation; the
affected sites may not be planted with maize the following year.
In addition, the sites must be treated with soil insecticides.
The area of infestation is continually monitored using pheromone
traps. When the pest is present, soil and plant parts are not
allowed to leave the controlled zone. Only after a certain
period of time is harvesting permitted.
No guarantee of success –
Genetic engineering as an alternative?
Some
experts believe that crop rotation isn’t enough to ward off
western corn rootworm infestation in the long term. Reports are
now coming in from North America that after thirty years of
maize, soybean crop rotations, beetles have adapted by laying
eggs and surviving in soybean fields.
European
research projects have found that the western corn rootworm can
feed on more than just maize. It was reported that beetles fed
on 73 percent of the weeds growing in tests fields. Because
maize dies off relatively early in the fall, it is thought that
the beetles must find alternative food sources. This enables the
pest to spread more easily, making containment a more difficult
challenge. The larvae can also survive on wild plants, making
crop rotation strategies unlikely to suffice in the long term.
The
shortcomings of crop rotation as a management strategy are
making farmers on both sides of the Atlantic open to newer, more
innovate approaches. Stefan Vidal of Göttingen University, a
coordinator for a EU project on the spread of the western corn
rootworm, is quite optimistic about the potential effectiveness
of transgenic
Bt maize in Europe. Based on the assumption that the
infestation rates in Europe could reach those currently seen in
the United States, he views chemical control methods and
transgenic maize as the only management strategies that can be
effective in regions of intensive maize cultivation.
Western corn rootworm
resistant Bt Maize: Already grown in the United States
The
genetically modified maize line known as MON 863 (YieldGard
Rootworm Corn) received approval in the US in 2003, giving
producers a new way to combat the western corn rootworm. The new
maize line, developed by the company Monsanto, was planted on
two million hectares in 2005.
Similar to
the well known Bt concept used to combat the European corn
borer, this genetically modified maize line also produces a
toxin (Bt toxin). The form of the Bt toxin expressed in MON 863
specifically targets the corn rootworm. The newly introduced
gene responsible for producing this toxin comes from the
bacterium
Bacillus thuringiensis (ssp. Kurmamotensis), an organism
commonly used to control pests on organic farms. MON 863
contains less Bt toxin than most Bt maize varieties, producing
the toxin primarily in the roots, which is the site of entry for
the western corn rootworm.
Approval of MON 863 in
Europe
In January
2006, the European Commission approved corn rootworm resistant
maize (MON 863) for food use. It also granted authorisation for
the import and industrial use of a cross between MON 863 and MON
810, a Bt maize line resistant to the
European corn borer.
The
approval process has sparked considerable debate over the safety
of MON 863. The controversy was set off by the findings of a
feeding study conducted on rats. Based on the data provided in
the approval application, which included the disputed feeding
studies,
EFSA declared that MON 863 is as safe as conventional maize
for consumption. However, scientists from France’s commission on
genetic engineering, CGB, expressed concerns that the MON 863
feeding tests may have revealed potentially pathological changes
to internal organs and signs of inflammation. Greenpeace
successfully petitioned the courts to mandate the public release
of documentation pertaining to the feeding studies. The results
of the experiment were reviewed once again by two independent
experts, and in the end, both EFSA and the CGB scientists came
to the conclusion that the differences observed between rats fed
conventional maize and those fed genetically modified maize did
not exceed the differences normally observed between any two
individuals. In any case, any differences were not biologically
relevant. EFSA substantiated its position in a second
recommendation, which was then used as the basis for the
European Commission’s approval decision.
European
approval committees are reviewing additional approval
applications for the import and feed use of various hybrids
derived from crosses between MON 863 and other maize lines.
Monsanto has not yet sought approval for growing MON 863 in
Europe. Three more western corn rootworm resistant maize lines
joined MON 863 and are currently awaiting approval: line MIR
604, line 59122, and line MON 88017. One of the lines, 59122, is
awaiting approval for cultivation in Europe. In years to come,
corn rootworm resistant maize could become a pest management
option for European farmers.
Strategies for preventing
resistance among pests: Successful to-date
Pests have
the potential to adapt to virtually every control method, which
sometimes makes methods that were at one time effective become
completely useless. MON 863 is no exception to this biological
dogma. This is why the American Environmental Protection Agency
(EPA) developed what is known as resistance management, which is
designed to delay the development of resistance and to detect
resistant pests as early as possible. Farmers in the US are
required to surround Bt maize fields with strips of non-Bt
maize, setting up areas called
refugia. These refugia allow non-resistant pests to survive.
If resistant individuals happen to be present, they should still
be able to find susceptible mating partners resulting in
susceptible offspring.
It was
expected that pests like the European corn borer and the cotton
bollworm would quickly develop resistance to Bt crops. However,
findings from a 2003 study led by Bruce Tabashnik at the
University of Arizona (Tucson, Arizona, USA) and at Cornell
University (Ithaca, New York, USA) suggest the opposite. The
study could not report a single Bt resistant pest. Even
Tabashnik, an entomologist, was surprised by his findings.
According to Tabashnik, everyone expected at least a slight
increase in resistance.
Studies in China report similar findings. Researchers have been
observing cotton bollworm populations over five years of Bt
cotton cultivation, and no signs of resistance have yet been
observed. These findings conflict with several non-scientific
reports of Bt resistant insects.
Some
countries in Europe have already begun research on the
ecological safety of corn rootworm resistant maize and on early
detection methods for resistance among the pests. One of the
goals of this research is to develop improved monitoring
procedures to implement in parallel to cultivation. In Germany,
for instance, researchers are investigating effects on
non-target organisms such as beetles, spiders, and aphids.
Equipped with these research findings, authorities will better
be able to detect potential unexpected negative ecological
consequences and to respond to them promptly.
© 2008 by
GMO Compass |
