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- ITHACA, New York (ENS) - An increasingly popular genetically engineered
commercial corn has pollen which kills monarch butterfly larvae in laboratory
tests, Cornell University researchers report. The corn produces a bacterial
toxin to protect against corn pests.
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- Writing in the May 20 of the journal
"Nature," the researchers note that this hybrid crop, known as
Bt-corn, has genes from the bacterium Bacillus thuringiensis (Bt) spliced
into the plant genes. This new gene produces a protein which kills insects
after the protein is ingested.
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- These hybrids are very effective against
the ravenous European corn borer, a major corn pest that is destroyed by
the plant's toxic tissue.
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- Unlike many pesticides, Bt-corn has been
shown to be generally safe for human consumption, although some critics
of biotechnology disagree. It has not been shown to have any harmful effect
on many non-target organisms - such as pollinating honeybees or beneficial
predators such as ladybugs.
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- But the Bt-modified corn produces pollen
containing crystalline endotoxin from the bacterium genes. This corn pollen
is dispersed by the wind around cornfields. It lands on other plants, including
milkweed which is the exclusive food of monarch caterpillars.
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- Like all grasses, corn is wind-pollinated,
and the pollen can be blown more than 60 yards from the edge of cornfields.
"Pollen is that yellow dusting your car gets on spring and summer
days; pollen is everywhere," says John Losey, Cornell assistant professor
of entomology and the primary investigator on the study. "That's why
we are concerned about this problem."
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- "Monarchs are considered to be a
flagship species for conservation. This is a warning bell," says co-researcher
Linda Rayor. "Monarchs themselves are not an endangered species right
now, but as their habitat is disrupted or destroyed, their migratory phenomena
is becoming endangered."
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- In the laboratory tests, monarchs fed
milkweed leaves dusted with so-called transformed pollen from a Bt-corn
hybrid ate less, grew more slowly and suffered a higher mortality rate.
Nearly half of these larvae died, while all of the monarch caterpillars
fed leaves dusted with the non-transformed corn pollen survived.
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- The toxin in the transformed pollen,
the researchers say, goes into the gut of the caterpillar, where it binds
to specific sites. When the toxin binds, the gut wall changes from a protective
layer to an open sieve so that pathogens usually kept within the gut and
excreted are released into the insect's body. As a result, the monarch
caterpillar quickly sickens and dies.
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- Before the advent of Bt-corn, the European
corn borer was extremely difficult to control because it bores into the
stalk, where it is protected from pesticides. It produces several generations
a year. Because it was so difficult to control effectively with pesticides,
annual losses averaged $1.2 billion. In contrast, Bt-corn provides essentially
total season-long control at a reasonable cost without the use of pesticides.
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- At least 18 different Bt-engineered crops
have been approved for field testing in the United States. As of last year,
transformed corn, potatoes and cotton had been approved by the U.S. Department
of Agriculture for commercial use.
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- Several factors make monarch caterpillars
particularly likely to make contact with corn pollen, Losey says. Monarch
larvae feed exclusively on milkweed because it provides protection against
predators. The plant contains cardenolides, which are toxic, bitter chemicals
that the monarch caterpillar incorporates into its body tissues, rendering
it unpalatable to predators.
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- Monarch caterpillars are feeding on milkweed
during the period when corn is shedding pollen, Losey says. "They
may be in the right place at the right time to be exposed to Bt-corn pollen."
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- Says Losey, "We need to look at
the big picture here. Pollen from Bt-corn could represent a serious risk
to populations of monarchs and other butterflies, but we can't predict
how serious the risk is until we have a lot more data. And we can't forget
that Bt-corn and other transgenic crops have a huge potential for reducing
pesticide use and increasing yields. This study is just the first step,
we need to do more research and then objectively weigh the risks versus
the benefits of this new technology."
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- With approval from the European Commission,
Ciba Seeds has been marketing its genetically modified Bt corn to the 15
member countries of the European Union since 1997.
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- The European Union's Scientific Committee
on Food, the Scientific Committee on Animal Nutrition and the Scientific
Committee for Pesticides concluded, "There is no reason to believe
that the genetic modification of the Bt-maize will give rise to adverse
effects on human health from its use in human food."
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- "There is no reason to believe that
the genetic modification of the Bt-maize will give rise to adverse effects
on animal health from its use in animal feed."
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- "A potential development of insect
resistance to the Bt toxin cannot be considered an adverse environmental
effect, as existing agricultural means of controlling such resistant species
of insects will still be available."
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- Environment News Service (ENS) 1999.
All Rights Reserved.
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