Case Study: Bt Corn Pollen and the Monarch Butterfly Controversy

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.



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.



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 students findings after doing the case study. Suggested questions for the post-case study discussion:


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


Steven Milloy. Butterfly Survivor, or


Monarch Butterfly Natural Enemies


Bt Corn and European Corn Borer Information


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 )


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 )


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).


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 )


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 )


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 )




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 g/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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