Case Study: Bt
Corn Pollen and the Monarch Butterfly Controversy
AgBiosafety.unl.edu
Copyright
University of Nebraska-Lincoln By
Doug Golick Website Coordinator |
|
Purpose: This is a case study introducing students to
a real controversy surrounding biotech crops and their effects on Monarch
butterflies. Students will review published materials and answer a series of
questions to help guide them in making science-based decisions on the true
affect of biotech crops on the Monarch butterfly. Students will be able to
apply some of the basic concepts learned in this lesson to other controversies
in the biotech world.
Objectives:
Upon completion of this lesson the students will:
Gain an increased understanding of hazard and risk.
Learn the potential complexity of issues involving risk.
Learn about risk assessment as it pertains to the monarch
butterfly controversy.
Demonstrate their understanding of argumentation and make a
conclusion about the monarch controversy.
Method:
1. 1. Students will be
introduced the Bt corn pollen and monarch butterfly controversy through
teacher led discussion (information provided in teacher background).
2. 2. Students will be
introduced to the concepts of hazard, risk, and risk assessment through teacher
led discussion (information provided in teacher background).
3. 3. Students will be
given the Case Study: Bt corn and the Monarch butterfly controversy.
4. 4. Students will
read papers (available through download or print Online) and answer the series
of questions provided in the case study assignment sheet.
5. 5. Students will
make a final assessment/decision about the risk and safety of Bt crops
and Monarch butterflies.
6. 6. Optional:
once assignment is submitted, teacher will lead a class discussion of the
student’s findings after doing the case study.
Suggested questions for the post-case study discussion:
7.
Are Bt crops
hazardous? If so, to which organisms?
Is the monarch butterfly at risk from the Bt corn
pollen?
Many other studies have been published on non-target insects
other than the monarch butterfly. Why do you think the Losey study received so
much attention? Is the monarch butterfly more important than the other insects?
Are there other reasons for this attention?
Given the results of the studies, what should the future
implications be for these crops?
Do they need to have the same amount of regulation? Do they
need to be regulated more strictly?
Developers of Bt corn crops received much bad publicity from
the Monarch controversy generated from the Losey paper. What could the
companies done to prevent this PR nightmare?
Assessment (see below)
Assessment students will be graded on effectiveness in
answering the questions in asked in the case study. Students will also be
graded on presentation of the written argument of the project.
Teacher Background:
In 1999 researchers from Cornell University published a
letter in the journal Nature that showed Bt corn pollen had toxic
effects on larvae of the monarch butterfly. The caterpillar, or larval stage,
of this insect feeds on milkweed plants. Because some milkweed grows next to
corn fields, Losey and his Cornell collegues suggested that Bt corn
pollen may drift onto milkweed and harm the monarch larvae. Although only a
note and not a full scientific investigation, the Cornell letter garnered a
tremendous amount of media coverage and gave anti-biotech advocates a poster
species for their cause. In the following year the EPA, biotech companies, and
university researchers studied the potential impact of Bt corn pollen on
the monarch butterfly and related species. Their research findings were
published in September 2001 in a series of papers(PNAS,
2001).
In this assignment students will be asked to review the
research articles starting with the Cornell study. After reading the article
students will be asked to answer a series of questions that will help them
assess the risk of the Bt corn pollen to the monarch butterfly. At the
end students will write a short summary of their conclusions stating an
assessment of the impact of Bt corn pollen to the monarch butterfly.
Articles for Review:
There are several articles that are included in this lesson.
If you feel that the list is too extensive for your students to read you may
exclude the Butterfly Survivor Article, Monarch Butterfly Natural Enemies, Bt
Corn and European Corn Borer Information, and Monarch Overwintering Web links.
These articles are meant to give the students a broader scope of the problem.
It is suggested that the instructor read all the articles for a better
understanding of the terms and articles surrounding this case study.
John E. Losey, Linda S. Rayor, Maureen E. Carter (Department
of Entomology, Cornell University). Transgenic
Pollen Harms Monarch Larvae . Nature, 399. May 20, 1999
http://www.biotech-info.net/transpollen.html
Steven Milloy.
Butterfly Survivor, Junkscience.com
http://junkscience.com/foxnews/fn082500.htm
or
http://www.biotechknowledge.com/showlib.php3?uid=3863
Monarch Butterfly Natural Enemies
http://www.monarchlab.umn.edu/Research/PNE/pne.html
Bt Corn and European Corn Borer Information
http://croptechnology.unl.edu/html/startLessonFrame.shtml?LessonID=994877762&category=CropGenetics
Selected Monarch Research Papers
Mark K. Sears, Richard L. Hellmich, Diane E. Stanley-Horn,
Karen S. Oberhauser, John M. Pleasants, Heather R. Mattila, Blair D. Siegfried,
and Galen P. Dively.
Impact of Bt
corn pollen on monarch butterfly populations: A risk assessment
PNAS published September 14, 2001, 10.1073/pnas.211329998 ( Agricultural
Sciences )
http://www.pnas.org/cgi/content/full/211329998v1
A. R. Zangerl, D. McKenna, C. L. Wraight, M. Carroll, P.
Ficarello, R. Warner, and M. R. Berenbaum Effects of exposure to event 176 Bacillus thuringiensis corn
pollen on monarch and black swallowtail caterpillars under field conditions
PNAS published September 14, 2001, 10.1073/pnas.171315698 ( Agricultural
Sciences )
http://www.pnas.org/cgi/content/full/171315698v1
Richard L. Hellmich, Blair D. Siegfried, Mark K. Sears,
Diane E. Stanley-Horn, Michael J. Daniels, Heather R. Mattila, Terrence
Spencer, Keith G. Bidne, and Leslie C. Lewis
Monarch larvae
sensitivity to Bacillus thuringiensis- purified proteins and pollen
PNAS published September 14, 2001, 10.1073/pnas.211297698 ( Agricultural
Sciences).
http://www.pnas.org/cgi/content/full/211297698v1
John M. Pleasants, Richard L. Hellmich, Galen P. Dively,
Mark K. Sears, Diane E. Stanley-Horn, Heather R. Mattila, John E. Foster,
Thomas L. Clark, and Gretchen D. Jones. Corn pollen deposition on milkweeds in and near cornfields
PNAS published September 14, 2001, 10.1073/pnas.211287498 ( Agricultural
Sciences )
http://www.pnas.org/cgi/content/full/211287498v1
Diane E. Stanley-Horn, Galen P. Dively, Richard L. Hellmich,
Heather R. Mattila, Mark K. Sears, Robyn Rose, Laura C. H. Jesse, John E.
Losey, John J. Obrycki, and Les Lewis
Assessing the
impact of Cry1Ab-expressing corn pollen on monarch butterfly larvae in field
studies. PNAS published September 14, 2001,
10.1073/pnas.211277798 ( Agricultural Sciences )
http://www.pnas.org/cgi/content/full/211277798v1
Karen S. Oberhauser, Michelle D. Prysby, Heather R. Mattila,
Diane E. Stanley-Horn, Mark K. Sears, Galen Dively, Eric Olson, John M.
Pleasants, Wai-Ki F. Lam, and Richard L. Hellmich. Temporal and spatial overlap between monarch larvae
and corn pollen. PNAS published September 14, 2001,
10.1073/pnas.211234298 ( Agricultural Sciences )
http://www.pnas.org/cgi/content/full/211234298v1
Assessment:
There are several ways this assignment can be assessed. The
assignment can be graded strictly on a point basis for correctly answered
questions and sufficiently supported argumentation. This would be the case in a
take home assignment per individual student or small group.
The assignment can also be used as a class discussion where
students form small groups to investigate the problem. Groups can then report
their results to the class and the instructor can regulate the discussion. In
this case learning can be assessed by participation at the group level.
The learning goals of this assignment can be seen if
students are able to demonstrate a conclusion about the real risk of Bt to
monarch, through a step-by-step assessment.
Answers to Student Handout Questions (Monarch Butterfly
Controversy Case Study)
1. 1. Research and find
the data for these items below.
a. a. Amount of
toxin expressed in the pollen of event 176 and
A: (1.1-7.1 µg/gm pollen)
b. b. The amount of
toxin needed to kill or significantly harm the development of the insect.
A: Depends on the Bt
event and the number of pollen grains monarch larva consume. Generally
event 176 expresses higher amount of protein per pollen grain as compared to
other events, so less consumption is needed to effect larva.
Information for all events found in
the Assessing the impact of Cry1Ab-expressing corn pollen on monarch
butterfly larvae in field studies paper.
c. c. What is the
likely-hood that a monarch larva will come in contact with the toxin.
A: Taken from PNAS paper Temporal
and spatial overlap between monarch larvae and corn pollen. Results
presented here have two important implications. First, a portion of the monarch
population is exposed to and probably consumes corn pollen that
collects on milkweed plants growing in cornfields. Recent research
suggests that the Bt corn hybrids most commonly planted produce
levels of toxin in their pollen that are unlikely to have severe
fitness consequences on monarchs (22-24), but our findings
indicate the need to evaluate future transgenic hybrids on the basis
of their protein toxicity and expression in pollen. Second,
regardless of risks imposed by transgenic corn, changes in
agricultural practices such as weed control or the use of foliar
insecticides could have large impacts on monarchs by affecting
milkweed density and condition, or monarch survival.
d. d. The amount of Bt
corn pollen found at the different distances from the field.
A: The level of Bt corn
pollen collected in tests dramatically decreased 5 meters away from fields,
suggesting that pollen will not collect on most milkweed at levels toxic to
monarch.
e. e. Information
about mortality of the Monarch (all the ways monarchs die naturally by
percentage monarchs die) expressed in a life-table. Is this information
available? Is it needed to determine the risk to the monarch butterfly?
A: No comprehensive life
tables exist for the monarch butterfly. Is this information needed to assess
the risk to the monarch. No, because the data gathered from tests shows that
risk of exposure to Bt corn pollen is low for most
monarchs. Life-tables would shed light on the
overall mortality rate and how bt toxin exposure resulted death fits into the
overall mortality as a percentage.
2. 2. What is the risk
to the monarch butterfly from Bt corn?
a. a. Do we have
enough data?
A: Yes
b. b. Do we need all
possible data to access the risk?
A: No, enough data exists to
determine risk
c. c. Identify
what the risk is to the monarch butterfly?
A: Generally the risk is low,
however Bt events such as 176 that express greater level of toxins per pollen
weight pose the greatest risk of all types tested.
3. 3. After analyzing
the data in the readings, what do you think the impact is to population from Bt
crops? Are there greater risks to Monarch butterflies other than Bt
crops? Justify your answer.
A: Impact on
the monarch is low.
A: Yes, there probably are greater risks to monarchs
than Bt corn pollen, i.e. habitat destruction, agriculture practices, cars
hitting monarchs on the highway etc.
4. 4. Are there other
insects that can be found in and around a corn field that may be harmed by Bt
crops engineered to kill European Corn Borers? List some examples.
A: Black swallowtails, tiger moths, other butterfly
or moths
5. If there are other insects that are at risk from Bt
exposure, why do you think Losey chose to focus his work on the monarch
butterfly?
A: Open to interpretation, however it should be noted the
monarch butterfly is perhaps the best known and loved of all insects. Any newly
discovered hazard would be big news and be of interest to both the press and
public.
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