Monarch Butterfly

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Issue in Brief:
Scientists: Bt corn is not a risk to monarch butterflies

Insect-resistant Bt plants incorporate genes from the soil microbe Bacillus thuringiensis that allow the plants to produce proteins that protect them from certain insect pests, among them the European corn borer, cotton and pink bollworms, tobacco budworm and Colorado potato beetle. This reduces the amount of pesticides farmers need to apply to control these pests.

The protein expressed in Bt corn has long been known to be toxic to the caterpillars (larvae) of butterflies, including the monarch, but it is harmless to humans, animals and most other insects. BT sprays have been used safely by farmers for decades.

In their larval stage, monarchs feed exclusively on milkweed plants, which grow in both natural habitats and in cultivated fields. In June 1999, a research letter was published in the journal Nature demonstrating the susceptibility of monarch larvae to Bt pollen. The study, which was conducted under laboratory conditions, exposed a small number of monarch caterpillars to milkweed heavily dusted with Bt corn pollen. This was soon followed by a paper in Oecologia that suggested natural levels of Bt corn pollen in the field were harmful to monarchs.

Questions immediately arose about the relevance of these studies to monarch populations in the wild. Data from other research studies, for example, showed that the concentration of pollen on the milkweed leaves in the Nature laboratory study was greater than could be expected in the field and that the monarch's migratory pattern generally does not bring it in contact with corn during the short time it sheds pollen.

To address the issues raised by the letter in Nature, a large group of scientists representing government, academia, industry and environmental groups was gathered in workshops held by USDA's Agricultural Research Service (ARS). In December 1999, ARS and the Agricultural Biotechnology Stewardship Technical Committee-comprising Aventis CropScience, American Crop Protection Association, Biotechnology Industry Organization, Dow AgroSciences, Monsanto, Novartis Seeds and Pioneer Hi-Bred International-provided grant funding for field research on the impact, if any, of Bt corn on monarchs.

Six teams of researchers published their results in the September 14, 2001, edition of the Proceedings of the National Academy of Sciences. After two years of study, the researchers found that the impact of Bt corn pollen on monarch butterfly populations is negligible. The research demonstrates that Bt corn poses little threat to monarchs because the pollen is not toxic in the concentrations that butterfly larvae would encounter under field conditions.

EPA approves Bt corn for an additional seven years; Notes risk of Bt corn to monarch butterfly "very low"

These peer-reviewed papers, together with data provided by biotechnology companies, contributed to the scientific basis for the Environmental Protection Agency's environmental assessment in its October 2001 Biopesticides Registration Action Document, which renewed the registration for Bt crops for seven years. The scientific evidence gathered by the EPA during its two-year-long review demonstrates that Bt corn does not harm monarch butterfly populations. Indeed, the EPA noted that some research suggests widespread planting of Bt corn could greatly benefit monarch butterfly survival by reducing use of pesticide sprays, which can affect beneficial, nontarget insects.

Resources:
Controversial Monarch Studies:

• Losey, J., Raynor, L., and Carter, M.E. 1999. Transgenic pollen harms monarch larvae. Nature 399: 214.
  Read the article here (requires paid subscription).
• Hansen Jesse, L.C., and Obrycki, J.J. 2000. Field deposition of Bt transgenic corn pollen: Lethal effects on the monarch butterfly, Oecologia 125: 241-248.
  Read the abstract here.

• Sears, M.K., et al. 2001. Impact of Bt corn pollen on monarch butterfly populations: A risk assessment. PNAS 98: 11937-11942.
• Zangerl, A.R., et al. 2001. Effects of exposure to event 176 Bacillus thuringiensis corn pollen on monarch and black swallowtail caterpillars under field conditions. PNAS 98: 11908-11912.
• Hellmich, R.L., et al. 2001. Monarch larvae sensitivity to Bacillus thuringiensis-purified proteins and pollen. PNAS 98: 11925-11930.
• Pleasants, J.M., et al. 2001. Corn pollen deposition on milkweeds in and near cornfields. PNAS 98: 11919-11924.
• Stanley-Horn, D.E., et al. 2001. Assessing the impact of Cry1Ab-expressing corn pollen on monarch butterfly larvae in field studies. PNAS 98: 11931-11936.
• Oberhauser, K.S., et al., 2001. Temporal and spatial overlap between monarch larvae and corn pollen. PNAS 98: 11913-11918.

• Scriber, J.M. 2001. Bt or not Bt: Is that the question? PNAS 98 (22): 12328.
• Wraight, C.L., Zangerl, A.R., Carroll, M.J., and Berenbaum, M.R. 2000. Absence of toxicity of Bacillus thuringiensis pollen to black swallowtails under field conditions. PNAS 97: 7700-7703.
• Pimentel, D.S., and Raven, P.H. 2000. Bt corn pollen impacts on nontarget Lepidoptera: Assessment of effects in nature. PNAS 97: 8198-8199.

• Bt Plant-Pesticides Biopesticides Registration Action Document, II Science Assessment, E. Benefits (October 15, 2001).
  "Overall, the available information indicates a very low probability of risk to monarchs in areas beyond the near edge of corn fields. Inside corn fields and at the near edge of corn fields there is low probability of monarch larvae encountering a toxic level of pollen for the Bt corn products covered by this risk assessment."
• Agricultural Biotechnology Stewardship Technical Committee-Non-Target Organism Subcommittee and Novigen Sciences, Inc., Amended Revised Response to EPA's Data Call-In Notice Concerning the Potential for Adverse Effects of Bt Corn on Non-Target Lepidopterans, Executive Summary and Preface (June 22, 2001).
  "Overall, consideration of hazard and exposure factors indicates that Bt corn pollen represents a low to negligible risk to monarchs and other non-target lepidopterans."
• FIFRA Science Advisory Panel, Issues Pertaining to the Bt Plant Pesticides Risk and Benefit Assessments (October 18-20, 2000).
• FIFRA Science Advisory Panel, Characterization and Non-Target Organism Data Requirement for Protein Plant-Pesticides and Cumulative Risk Assessment Methodology Issues of Pesticide Substances that Have a Common Method of Toxicity (December 8-9, 1999).

• U.S. Department of Agriculture, Butterflies and Bt Corn: Allowing Science to Guide Decisions.
• American Academy of Microbiology, 100 Years of Bacillus thuringiensis: A Critical Scientific Assessment (2002).
• Gatehouse, A., Ferry, N., and Raemaekers, R. 2002. The case of the monarch butterfly: A verdict is returned. Trends in Genetics 18(5): 249-251.
  Read the abstract here (requires registration).
• Minorsky, P. 2001. The monarch butterfly controversy. Plant Physiology 127: 709-710.
• Pew Initiative on Food and Biotechnology, Three Years Later: Genetically Engineered Corn and the Monarch Butterfly Controversy (2002).
• Shelton, A.M., and Sears, M.K. 2001. The monarch butterfly controversy: Scientific interpretations of a phenomenon. The Plant Journal 27(6): 483-488.
• Colorado State University, Department of Soil and Crop Science, Transgenic Crops: An Introduction and Resource Guide-Monarch Butterflies and Bt Corn.
• Monarch Watch.
  A good source for detailed information on all aspects of the monarch.

For more links, click here.

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