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2-Plants: GM corn can kill Monarch butterfly, Cornell University (US) announces



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TITLE:  Engineered corn can kill Monarch butterflies
SOURCE: Cornell University News Service
DATE:   May 19, 1999

----------------- archive: http://www.gene.ch/ ------------------


ENGINEERED CORN CAN KILL MONARCH BUTTERFLIES

ITHACA, N.Y. - An increasingly popular commercial corn,
genetically engineered to produce a bacterial toxin to protect
against corn pests, has an unwanted side effect: Its pollen kills
monarch butterfly larvae in laboratory tests, according to a
report by Cornell University researchers. Writing in the latest
issue (May 20) of the journal Nature, the Cornell researchers
note that this hybrid crop, known as Bt-corn, has genes from the
bacterium Bacillus thuringiensis (Bt) spliced into the plant
genes. These hybrids are very effective against the ravenous
European corn borer, a major corn pest that is destroyed by the
plant's toxic tissue. The engineered corn is safe for human
consumption.

Unlike many pesticides, the Bt-corn has been shown to have no
effect on many "nontarget" organisms - pollinators such as
honeybees or beneficial predators of pests like ladybugs. But the
Bt-modified corn produces pollen containing crystalline endotoxin
from the bacterium genes. When this corn pollen is dispersed by
the wind, it lands on other plants, including milkweed, the
exclusive food of monarch caterpillars and commonly found around
cornfields.

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 E. Losey, Cornell assistant
professor of entomology and the primary investigator on the
study. "That's why we are concerned about this problem."

Other researchers on the study were Linda S. Rayor, Cornell
instructor in entomology, and Maureen E. Carter, Cornell research
aide. "Monarchs are considered to be a flagship species for
conservation. This is a warning bell," says Rayor. "Monarchs
themselves are not an endangered species right now, but as their
habitat is disrupted or destroyed, their migratory phenomena is
becoming endangered."

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, the researchers
report. Nearly half of these larvae died, while all of the
monarch caterpillars fed leaves dusted with nontransformed corn
pollen or fed leaves without corn pollen survived the study.

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 caterpillar quickly sickens and dies. Bt
engineered corn is among the first major commercial successes for
agricultural biotechnology. Last year, more than 7 million acres
of the hybrid crop were planted by U.S. farmers primarily to
control the European corn borer. Before the advent of Bt-corn,
this pest 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. 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.

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. Milkweed
grows best in "disturbed" habitats, like the edges of cornfields,
Losey notes.

The butterflies overwinter in Mexico and by the spring begin
migrating north. The first generation of the year crosses into
Texas, other Gulf Coast states and Florida, seeking milkweed on
which to lay their eggs and feed. By late May or early June, the
second generation of adults has emerged and heads north to areas
including the Midwest Corn Belt. Monarch caterpillars are feeding
on milkweed during the period when corn is shedding pollen, Losey
says. Thus "they may be in the right place at the right time to
be exposed to Bt-corn pollen."

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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