|
|
|
|
Back |
|
|
There is no significant risk to monarch butterflies from
environmental exposure to Bt corn, according to research conducted by a group
of scientists coordinated by the Agricultural Research Service (ARS), U.S.
Department of Agriculture. This research was published in the Proceedings of
the National Academy of Sciences (PNAS).
That Bt corn might present a risk became a matter of scientific
and public concern when a small experiment in 1999 indicated caterpillars
suffered when given no choice but to feed on milkweed leaves heavily dusted
with Bt corn pollen.
The issue focused on the pollen of Bt corn because it, like any
corn pollen, can blow onto milkweed leaves, which are the exclusive diet of
monarch caterpillars.
Two major questions needed to be answered to determine whether
there was any actual risk to monarch caterpillars from the Bt pollen:
How much Bt corn pollen
does it take before there are any toxic effects on caterpillars?
What is the
likelihood that caterpillars might be exposed to that much pollen?
The studies in this project showed that monarch caterpillars have
to be exposed to pollen levels greater than 1,000 grains/cm2 to show
toxic effects.
Caterpillars were found to be present on milkweed during the one
to two weeks that pollen is shed by corn, but corn pollen levels on milkweed
leaves were found to average only about 170 pollen grains/cm2 in
corn fields.
Reports from several field studies show concentrations much lower
than that even within the cornfield. In Maryland, the highest level of pollen
deposition was inside and at the edge of the corn field, where pollen was found
at about 50 grains/cm2. In the Nebraska study, pollen deposition
ranged from 6 grains/cm2 at the field edge to less than 1
grain/cm2 beyond 10 meters. Samples collected from fields in Ontario
immediately following the period of peak pollen shed showed pollen
concentrations averaged 78 grains at the field edge.
|
Back |
|
|
The cooperation between researchers
from many separate institutions was extraordinary, from planning through
publication, to address this issue that came up suddenly and which had drawn
such public concern. The way in which this research was done is being
considered as a model for conducting risk assessment research.
Research priorities were set at an ARS-organized workshop in
Kansas City, MO, in February 2000 through discussions among scientists from
government, universities, industry, and environmental groups. The idea was to
ensure that all of the most important questions were covered.
Exchanges of information between butterfly biologists, corn
experts, pest specialists and others helped ensure that studies reflected how
monarchs actually interact with Bt corn. Through the workshops and other
discussions, the scientists also standardized many of their methods so that
data could be easily pooled to provide the most complete picture possible.
For example, by standardizing how collected pollen was treated,
data from several scientists' studies were compatible, providing a much larger
sample size and therefore more reliable results.
In another example, scientists from different areas were able to
combine data they collected about when pollen is shed from Bt corn in various
geographic regions. This allowed them to construct a complete picture of the
overlap of the time when pollen is shed across the major corn growing areas of
the United States and Canada and the hatching of monarch butterfly eggs.
Even publication of this research was handled in an unusual,
coordinated fashion. The researchers themselves pooled their data and results,
divided the data in logical sections, and agreed to submit all manuscripts
together to a single scientific journal for peer review. By publishing
exposure, toxicity and risk analysis studies at one time in one journal, it
allows scientists and policy makers to more easily evaluate the facts.
All of the studies published by this group have undergone critical
peer review by independent experts to ensure the validity of the scientific
methods, analysis and conclusions.
This type of cooperative research and scientific publication is
being seen as a model for conducting risk assessment research. By working
together, the researchers were able to share expertise, more data were
accumulated more quickly, and they were able to present a more complete
assessment of the potential for risk.
|
Back |
|
|
A small, preliminary study done at Cornell University, and
reported as a note in Nature in June 1999, indicated that monarch
butterflies under laboratory conditions might be harmed by eating pollen from
Bt corn plants. That experiment used a small number of caterpillars and gave
them no choice about avoiding eating leaves that had been treated with a thick
layer of Bt corn pollen. It did not attempt to duplicate real world
environmental conditions.
|
Back |
|
|
A large, informal group of scientists came together in workshops
held by ARS to discuss the questions posed by the note in Nature. This
included scientists from ARS, universities, industry and environmental
organizations.
In December 1999, ARS and the Agricultural Biotechnology
Stewardship Technical Committee (ABSTC) each contributed $100,000 to a grant
pool to fund research. ABSTC is a consortium of agricultural biotechnology
companies and associations including Aventis CropScience, American Crop
Protection Association, Biotechnology Industry Organization, Dow AgroSciences,
Monsanto, Novartis Seeds, and Pioneer Hi-Bred International.
Grants were selected by a steering committee consisting of
Adrianna Hewings, Midwest Area Director, ARS-USDA; Eldon Ortman, Purdue
University; Eric Sachs, Monsanto; Mark Scriber, Michigan State University; and
Margaret Mellon, Union of Concerned Scientists.
The senior authors on the scientific journal articles published in
the Proceedings of the National Academy of Sciences coordinated the
analysis of data and the writing of the papers:
Monarch larvae sensitivity to Bacillus thuringiensis-purified
proteins and pollen. Richard L. Hellmich, Corn Insects and Crop
Genetics Unit, Agricultural Research Service-U.S. Department of Agriculture,
Ames, Iowa; (515) 294-9343, fax (515) 294-2268, e-mail
rlhellmi@iastate.edu.
http://www.pnas.org/cgi/content/full/211297698v1
Impact of Bt corn pollen on monarch butterfly populations: A
risk assessment. Mark K. Sears, Department of Environmental Biology,
University of Guelph, Ontario, Canada; (519) 824-4120 ext. 3921, fax (519)
837-0442, e-mail msears@evb.uoguelph.ca.
http://www.pnas.org/cgi/content/full/211329998v1
Corn pollen deposition on milkweeds in and near
cornfields. John M. Pleasants, Department of Zoology and Genetics, Iowa
State University, Ames; (515) 294-7204, fax (515) 294-8457, e-mail
jpleasan@iastate.edu.
http://www.pnas.org/cgi/content/full/211287498v1
Assessing the impact of Cry1Ab-expressing corn pollen on
monarch butterfly larvae in field studies. Diane E. Stanley-Horn,
Department of Environmental Biology, University of Guelph, Ontario, Canada;
(519) 824-4120 ext. 4847, fax (519) 837-0442, e-mail
destanle@uoguelph.ca.
http://www.pnas.org/cgi/content/full/211277798v1
Temporal and spatial overlap between monarch larvae and corn
pollen. Karen S. Oberhauser; Department of Ecology, Evolution and
Behavior, University of Minnesota, St. Paul, Minnesota (612) 624-8706, fax
(612) 624-6777, e-mail oberh001@tc.umn.edu.
http://www.pnas.org/cgi/content/full/211234298v1
Many other scientists contributed to each paper and to the
important discussions that helped advance the research.
|
Back |
|
|
One Bt corn variety or eventBt 176was found to have
some negative effects on monarch caterpillars with pollen concentrations of
only 10 grains/cm2. Bt 176 was the earliest developed Bt corn and
was quickly supplanted by other types; it has never been planted on more than 2
percent of all the acres planted with corn. It likely will be phased out by
2003.
|
Back |
|
|
The U.S. Environmental Protection Agency considered data on Bt
corn's impact on nontarget organisms according to their 1995 fact sheet (U.S.
Environmental Protection Agency Publ. No. EPA731-F-95-004) and found no threat.
But the note published in Nature raised new concerns, especially with
the public. This research provides reliable scientific information on which any
new regulatory decision should be based.
|
Back |
|
|
The use of Bt corn needs to be considered compared to the
alternatives, rather than in a vacuum. Bt corn was developed as a way of
providing corn with natural resistance to some pests, particularly the European
corn borer and to a lesser extent the corn earworm, the southwestern corn
borer, and the lesser cornstalk borer.
Before the commercial introduction of Bt corn in 1996, the
European corn borer was only partially controlled using chemical insecticides.
Timing of applications for control was difficult, so farmers either accepted
yield losses or used more applications. In addition, pesticides often damage
nontarget insects.
Since Bt corn was introduced, use of pesticides recommended for
European corn borer control decreased from 6 million to slightly over 4 million
acre treatments in 1999, a drop of about one-third, according to the
Environmental Protection Agency.
|
Back |
|
|
When the research began, scientists believed that monarch
butterflies laid their eggs on milkweed that grows on the edges of cornfields.
This was the reason for studying how much and how far corn pollen is blown by
the wind outside of the fields.
They were surprised to find that many monarch butterflies lay
their eggs on milkweed plants growing within the fields. So researchers then
had to check pollen concentrations on leaves within the cornfields to see if
pollen accumulations were higher there.
Another unexpected finding was that pollen used for studies could
be contaminated by ground up anthers (anthers are the organ at the end of the
plant stamen that produces pollen) unless specifically handled to avoid the
contamination. Grinding the anthers released a much greater amount of Bt
protein, making the pollen appear to be more toxic to caterpillars during
laboratory studies.
While anthers are found on milkweed leaves in the environment, the
anthers are not ground up. Young caterpillars are too small to eat anthers,
which means they are not exposed to the higher level of Bt protein. ARS
entomologist Richard Hellmich compares a young caterpillar trying to eat an
anther to a person trying to eat a car.
When scientists simply sieved the pollen to remove the
contaminating anthers, the detrimental effects on caterpillars disappeared.
|
Back |
|
|
There is always a next question for researchers to answer. But
the question of whether Bt corn pollen poses an immediate significant risk to
monarch butterflies has been answered.
|
Back |
|
|
Studies are now under way to determine if there are subtle
effects that could occur when caterpillars are exposed to Bt corn pollen for
longer periods. In addition, studies are also being done to check whether older
caterpillars unintentionally eat corn anthers that fall onto milkweed leaves.
|
Back |
|
|
Habitat destruction; mowing of highway rights-of-way, ditches,
and pastures, which destroy milkweed; collisions with cars and trucks; and
insecticides all reduce monarch populations. The most common fatality for
monarch caterpillars is being eaten by other insects. Fewer than 10 percent of
caterpillars make to it to adulthood.
All of the factors, including Bt pollen, should be weighed in
proportion to the documented mortality that they cause.
|
Back |
|
|
Proceedings of the
National Academy of Sciences:
Monarch larvae sensitivity to Bacillus
thuringiensis-purified proteins and pollen. Richard L. Hellmich, Corn
Insects and Crop Genetics Unit, Agricultural Research Service-U.S. Department
of Agriculture, Ames, Iowa; (515) 294-9343, fax (515) 294-2268, e-mail
rlhellmi@iastate.edu.
http://www.pnas.org/cgi/content/full/211297698v1
Impact of Bt corn pollen on monarch butterfly populations: A
risk assessment. Mark K. Sears, Department of Environmental Biology,
University of Guelph, Ontario, Canada; (519) 824-4120 ext. 3921, fax (519)
837-0442, e-mail msears@evb.uoguelph.ca.
http://www.pnas.org/cgi/content/full/211329998v1
Corn pollen deposition on milkweeds in and near
cornfields. John M. Pleasants, Department of Zoology and Genetics, Iowa
State University, Ames; (515) 294-7204, fax (515) 294-8457, e-mail
jpleasan@iastate.edu.
http://www.pnas.org/cgi/content/full/211287498v1
Assessing the impact of Cry1Ab-expressing corn pollen on
monarch butterfly larvae in field studies. Diane E. Stanley-Horn,
Department of Environmental Biology, University of Guelph, Ontario, Canada;
(519) 824-4120 ext. 4847, fax (519) 837-0442, e-mail
destanle@uoguelph.ca.
http://www.pnas.org/cgi/content/full/211277798v1
Temporal and spatial overlap between monarch larvae and corn
pollen. Karen S. Oberhauser; Department of Ecology, Evolution and
Behavior, University of Minnesota, St. Paul, Minnesota (612) 624-8706, fax
(612) 624-6777, e-mail oberh001@tc.umn.edu.
http://www.pnas.org/cgi/content/full/211234298v1
Effects of exposure to event 176 Bacillus thuringiensis corn
pollen on monarch and black swallowtail caterpillars under field conditions.
M. R. Berenbaum, Department of Entomology, University of Illinois at
Urbana-Champaign, Urbana, Illionois; (217) 333-7784, fax (217) 244-3499, e-mail
maybe@uiuc.edu. http://www.pnas.org/cgi/content/full/171315698v1
|
|
Other
Links
Bt corn and European Corn Borers
http://www.extension.umn.edu/distribution/cropsystems/DC7055.html#contents
|
|
Butterflies and Bt Corn: Allowing Science to Guide Decisions
http://www.ars.usda.gov/sites/monarch
|
|
EPA Biopesticides Registration Action Document: Bacillus
thuringiensis Plant-Incorporated Protectants
http://www.epa.gov/pesticides/biopesticides/pips/bt_brad.htm
|
|
Monarch and Migration, Science Museum of Minnesota
http://www.smm.org/sln/monarchs/top.html
|
|
Monarch Watch http://monarchwatch.org/
|
[Top]
|
|
|
|
|