This is the /SF Chronicle/ version of a story I'm sure many of you
have seen already today, in /Nature/ or elsewhere. It was front-page
news in the NYT this a.m.
------- Forwarded Message Follows -------
Gene-Spliced Corn Imperils Butterfly
Caterpillars in study die after eating bioengineered plant pollen
Glen Martin, Chronicle Staff Writer Thursday, May 20, 1999
Scientists have discovered that pollen from genetically manipulated
corn could be killing native butterfly caterpillars in the Midwest,
casting a shadow over the emerging industry of bioengineered crops.
Although the discovery, reported today in the journal Nature, must
be confirmed by more field studies, the authors of the study said it
is a warning that agricultural biotechnology may have unintended
In the laboratory study, a group of Cornell University entomologists
found that pollen from corn infused with genes from the bacterium
Bacillus thuringiensis (Bt) is toxic to monarch butterfly larvae when
lightly sprinkled on milkweed, the natural food source for the
Bt is a natural bacterium that is fatal to caterpillars and other
larvae. When its genes are spliced into those of corn, a plant
results that produces Bt toxins in its tissues, killing corn borers
and other worm-like pests. Bt corn is considered safe for human
Under laboratory conditions, almost half of the monarch caterpillars
that ate milkweed dusted with Bt corn pollen died after four days,
the Cornell team found.
That compares with a 100 percent survival rate for caterpillars that
ate milkweed that either was free of pollen or was sprinkled with
pollen originating from corn that did not have Bt genes.
The implications of the study are ominous. Half of North America's
eastern monarch butterfly population is concentrated in the ``corn
belt.'' And about 20 percent of the U.S. corn crop, or about 8 million
acres, is planted in bioengineered Bt corn, a figure that grows every
While the plant strains have been credited with greatly reducing
pesticide use, any ``drift'' of pollen could prove devastating for
native butterflies and moths. Bt is harmless to most insects, but it
obliterates caterpillars and other larvae.
Linda Rayor, one of the authors of the study, observes that corn is
wind pollinated -- meaning its pollen is carried by the wind rather
than by bees and other insects.
``When you have a toxin freely dispersed by the wind, it could affect
any moth or butterfly larvae feeding near a cornfield,'' Rayor said.
``Our article isn't meant to be alarmist -- but it is a warning, a
flag of concern.''
The study could mean that monarch butterflies are at particular risk.
Populations of these big, orange and black migratory butterflies have
been in steep decline because of pesticide use and habitat
Some environmentalists said the study is an indication agribusiness
should go slowly in promoting transgenic crops.
``I think this clearly shows transgenic corn could be a serious
threat to monarchs,'' said Rebecca Goldburg, a senior scientist with
the New York-based Environmental Defense Fund. ``I doubt if it would
push them over the edge by itself, but it adds substantially to the
other risks they face.''
But Sarah Hake, a plant geneticist specializing in corn, said she is
unsure if the study is valid for field conditions.
``There is a lot of wind outdoors, and corn pollen doesn't usually
stick to plants in heavy concentrations, particularly if any distance
is involved,'' said Hake, who directs the Plant Gene Expression Center
in Albany, California, for the U.S. Department of Agriculture. ``I
think it would be difficult to mimic the actual concentrations you'd
see under natural conditions. We need to see field research on this
now before we can draw any firm conclusions.''
Rayor said Cornell researchers plan to conduct field research this
summer, but added that her group took pains to reproduce pollen
concentrations expected for milkweed located about 60 yards from a
cornfield. Corn pollen typically drifts 60 to 100 yards from the
plant under windy conditions.
Even if Bt corn could be adversely affecting certain butterflies, say
some scientists, those effects must be weighed against the dire
environmental effects of heavy pesticide use.
The Bt bacteria, which occurs naturally and breaks down rapidly in
the environment, was developed as an alternative to chemical
pesticides. Anecdotal reports indicate that Bt cornfields are much
richer in insect and avian life than Bt-free corn that is sprayed
regularly with poisons.
``I essentially believe those reports,'' said Arthur Shapiro, a
professor of entomology, ecology and evolution at the University of
California at Davis. ``There is no such thing as a risk-free
technology. Everything involves trade-offs, and we need to make the
best decisions we can based on the best information we have.''
Jay Byrne, a spokesman for Monsanto Co., a St. Louis chemical and
agricultural products firm that produces Bt corn, said his company
supports further research on the matter.
``We need to objectively assess the risk,'' Byrne said, ``and we have
to do everything possible to reduce any risk that exists. But along
with many scientists, we are not convinced that laboratory conditions
are the same as field conditions. And we should also remember that Bt
crops are reducing pesticide use by hundreds of thousands of gallons
annually. That is a very substantial environmental benefit.''
John E. Losey, the primary investigator of the Cornell report, agreed
``We need to look at the big picture here,'' he said. ``Pollen from
Bt corn could represent a serious risk to monarchs and other
butterflies, but we can't predict how serious that 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
NEW THREAT TO THE MONARCH
Increasingly, farmers are planting a genetically altered form of corn
that protects itself from pests by producing a toxin. The plants were
thought to be harmless to nonpest insects. But researchers report that
the plants produce a wind-borne pollen that can kill monarch
butterflies. The pollen is blown onto milkweed, which is food for the
monarch butterfly (top right) and the similar queen butterfly (larvae
at right). The crop could prove to be a serious threat because the
nation's corn belt is the heart of the monarch's breeding range.
c1999 San Francisco Chronicle Page A1
Michele Gale-Sinex, communications manager
Center for Integrated Ag Systems
UW-Madison College of Ag and Life Sciences
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