Pollen from Bt maize Can Kill Monarch Butterflies
Maize engineered to produce the Bacillus thuringiensis bacterial toxin to
protect against pests, has an unwanted side effect: its pollen kills monarch
butterfly (Danaus plexippus) larvae in laboratory tests, according to a
report by Cornell University researchers.
Writing in Nature, the researchers note that Bt maize has been shown to have
no effect on many "nontarget" organisms -- pollinators such as honeybees or
beneficial predators of pests such as ladybirds. But the Bt maize 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 (Asclepias sp.), the exclusive food of monarch
caterpillars and commonly found around maize fields.
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 non-transformed corn pollen or fed leaves without maize pollen survived
the study.
The toxin in the transformed pollen, 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.
Says John E. Losey, Cornell assistant professor of entomology and the
primary investigator on the study: "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."
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."
Bt-engineered maize is among the first major commercial successes for
agricultural biotechnology. Last year, more than 7 million acres of the
hybrid crop were planted by US 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-maize 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
USA. Several factors make monarch caterpillars particularly likely to make
contact with maize 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
maize fields, 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."
Field studies presented by Iowa State University scientists at a recent
conference also suggest that Bt maize pollen is harming monarch butterflies
Laura Hansen, graduate research assistant, and John Obrycki, professor of
entomology determined the amount of pollen deposited on milkweed leaves at
various distances from a Bt maize field. Leaf samples taken from within and
at the edge of the field were used to assess mortality of first instar
butterflies exposed to Bt and non-Bt maize pollen. Within 48 hours, they
found 19% mortality in the Bt corn pollen treatment compared to 0% on non-Bt
corn pollen exposed plants and 3% in the no pollen controls.
The Cornell study "proves without doubt that genetically modified crops pose
a potentially lethal threat to wildlife," say Friends of the Earth. "FoE has
been saying for years that Bt plants are not an ecological solution to pest
control. They can produce toxin in all parts of the plant, including pollen
which can be spread over a wide area, and therefore adversely affect benign
and beneficial insects, as this research demonstrates only too clearly" said
Gill Lacroix of FoE Europe's Biotechnology Programme.
Environmentalists in Mexico urged the government to ban imports and use of
GM maize. Homero Aridjis, head of the Group of 100 artists group said that
Mexico, the USA and Canada are obliged to protect the monarch butterfly
under ecological preservation provisions of the North American Free Trade
Agreement. The Mexican government has approved the experimental cultivation
of GM maize in certain regions.
"This new research confirms the views put forward by English Nature last
year that there are serious concerns about the commercial introduction of GM
crops before research has been done on their potential effects on
biodiversity," it says.
Responding to the Nature article, Monsanto highlighted the reduction in
spraying with insecticides that had resulted from Bt maize "as a result, the
effects on beneficial and other non-target insects also are dramatically
reduced or
eliminated." In a statement, the company said "We take very seriously
research on Monarch butterflies and other non-target species, as well as
beneficial insects that help control pests in fields. Considered in total,
research conducted in the field supports the safety of Bt crops for
beneficial and other non-target insects. The laboratory study in Nature
provides interesting information, but reflects a situation very different
than that actually prevalent in the natural environment.
Monarch larvae feed almost exclusively on milkweed. The natural habitat for
milkweed is prairies, fields and roadsides, not the middle of full grown and
pollinating corn fields. In real life situations, the exposure
of milkweed to corn pollen is very low because only a very small portion of
milkweed grows in close enough proximity to corn fields for exposure to corn
pollen. This information supports the conclusion of a very low likelihood of
effect of Bt pollen on non-target insects like the Monarch butterfly in
their natural habitats.
Monsanto also said that it was participating in an industry effort to
support additional field research to reaffirm the lack of impact of Bt crops
for non-target and beneficial insects in their natural environment.
Val Giddings of the BioIndustry Organization argued that "Even if the
reported results are validated, there are strong reasons to believe they are
not relevant to Monarch caterpillars in the wild".
"Monarch migration and egg laying patterns ensure that the primary period of
larval feeding and growth throughout nearly all the Monarch range takes
place well before any nearby corn produces pollen. Ongoing monitoring of Bt
corn fields by companies since their introduction further shows that very
little pollen lands on adjacent milkweed leaves. It is thus highly likely
that in the natural setting, outside the laboratory, most Monarch larvae
would never encounter any significant amounts of corn pollen. This means the
real potential for any negative impact is negligible.
"Ongoing monitoring by companies of Bt corn fields since their introduction
also shows that insect biodiversity and population densities in Bt corn
fields is significantly higher than in fields treated with chemical
pesticide sprays. Bt corn thus helps enhance beneficial insect populations
that would otherwise be threatened by the use of pesticidal sprays. This
further leads to significant improvements to water quality and environmental
conservation for insect eating birds, small mammals and other life."
"Reports of the potential for effects from these Bt corn hybrids on Monarch
butterflies or other lepidoptera are not new. They have been reported in the
scientific literature and regulatory review documents since at least 1986.
Both the Environmental Protection Agency and the US Department of
Agriculture have been provided data on the potential for impacts on
non-target species from Bt pollen for years. Their analyses indicated that,
when compared with the numerous other relevant factors, the impacts from
such pollen were likely to be negligible. "
"The key issue is how large an impact is likely, and how significant would
such an impact be when compared with the numerous other significant factors
known to have impacts on Monarch ranges and numbers."
"BIO members have long been working with groups concerned with Monarch
butterfly conservation to address the threats they face. It is widely
recognized that the principal threat facing the Monarch butterfly relates to
loss of vital winter habitat in southern California and the highlands of
central Mexico."
Novartis, the first company to market Bt maize said that the study does not
give any basis for a change in its marketing of Bt maize.
The paper, Transgenic pollen harms monarch larvae appears by John E. Losey,
Linda, S. Rayor and Maureen E. Carter, appears in Nature (1999) 399, 214.
Contact: John E. Losey, Entomology Dept, 4126 Comstock Hall, Cornell
University, Ithaca, NY 14853, USA
Tel: +1 (607) 255 7376
Fax:+1 (607) 255 0939
Email [EMAIL PROTECTED]
L. Hansen, Iowa State University, Ames , IA 50011 and J. Obrycki, Iowa State
University, Ames, IA 50011
Email [EMAIL PROTECTED]
http://www.pme.iastate.edu/info/monarch.htm
May 1999
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