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"Bt corn" refers to corn that has been enhanced through plant biotechnology with a trait that protects it from damage against specific insect pests such as the European corn borer, which can have devastating and irreversible effects on corn crops.
Bt corn and other insect-protected
crops derived through biotechnology are regulated by the Environmental
Protection Agency (EPA) to make sure their use causes no unreasonable adverse
effects on the environment, non-target insects and other life.
In laboratory feeding experiments last year, Dr. John Losey and other Cornell University researchers confirmed what scientists and regulators working with Bt corn already understood; namely, that Bt protein at certain doses is toxic to butterflies. The researchers suggested that this hazard, if demonstrated in the natural environment, could pose a risk to monarch butterflies that migrate through the central U.S., where the majority of corn is grown.
Last year, researchers in the U.S. and Canada conducted numerous field tests to investigate the potential effects of Bt corn on monarch butterflies. In February of this year, scientists gathered in Kansas City to discuss the latest findings in a workshop sponsored by the U.S. Department of Agriculture. In sum, the studies show that exposure levels under field conditions is very low. Multiple researchers working independently of one another in various geographic locations found the following:
- Exposure of monarch butterflies to Bt corn pollen under field conditions is well below
the level which would cause harm.
- The concentration of
pollen drops off very rapidly a short distance from the cornfield.
- Monarch butterflies tend not to eat pollen on
milkweed leaves.
- Climatic conditions and other factors can greatly
reduce exposure to pollen on milkweed leaves.
- Periods of monarch migration and pollen shed may not
overlap.
- New studies provide assurances about the affect of Bt corn pollen on non- monarch species.
- The Bt pollen hazard to
monarch butterflies in the laboratory does not translate into risk in nature.
- The Bt-monarch situation was also carefully evaluated by the EPA in a detailed summary of data on the risks and benefits of Bt products. This summary was prepared in anticipation of the agency. s re-registration review of Bt products. Notably, the EPA found that "Milkweeds in cornfields to within 1 meter of cornfields are unlikely to be dusted with toxic levels of Bt pollen& .The Agency
concludes that the published preliminary monarch toxicity information is not sufficient to cause undue concern of widespread risk to monarch butterflies at this time." The summary went to note that "& one needs to factor in the preliminary data showing that there is no pollen shed and monarch breeding overlap in most of the corn belt& "
Along these same lines, researchers David Pimentel and Peter Raven noted of Bt corn that the results of a University of Illinois study, "& demonstrated that Bt corn pollen from this corn strain is not toxic to this species of butterfly at levels observed in the field no matter how close the larval food plants were to the pollen-shedding corn plants." Pimentel and Raven observed further that, "Compared with the threats posed to Monarch butterflies by [insecticides and habitat destruction], and considering the gains obviously achieved in the level of survival of Monarch butterflies and other insects by eliminating a large proportion of the pesticides applied to the same crops, the widespread cultivation of Bt corn may have huge benefits for Monarch butterfly survival."
Regarding the threat to the Monarch butterfly larvae by Bt corn pollen, the House Subcommittee on Basic Research, which held comprehensive hearing on agricultural biotechnology, concluded that:
The threat posed by pest-resistant crop varieties developed using agricultural biotechnology to the Monarch butterfly and other non-target species has been vastly overblown and is probably insignificant.
For more information on the research materials used to prepare this paper, consult:
EPA Fact Sheet for Bacillus thuringiensis subspecies kurstaki Cry1A(b) delta endotoxin and its controlling sequences in corn. March 21, 1995 (Ciba Seeds).
EPA Fact Sheet for Bacillus thuriginensis subspecies kurstaki Cry1A(b) delta endotoxin and its controlling sequences as expressed in corn. December 20, 1996 (Monsanto).
EPA Registration Eligibility Decision (RED) Bacillus thuringiensis. EPA 738-R-98-004, March 1998.
Losey, J.O., L. Raynor and M.Carter. 1999. Transgenic pollen harms monarch larvae. Nature. 399:214.
MacIntosh, Stone, Sims, Hunst, Greenplate, Marrone, Perlak, Fischhoff and Fuchs. (1990): Specificity and efficacy of purified Bacillus thuringiensis proteins against ergonomically important insects. J. Invert. Pathol. 56:258-266.
McClintock, J.T., C.R. Schaffer and R.D. Sjoblad. 1995. A comparative review of the mammalian toxicity of Bacillus thuringiensis-based pesticides. Pestic. Sci. 45:95-105.
Orr and Landis. 1997. Oviposition of European corn borer (Lepidoptera: Pyralidae) and impact of natural enemy populations in transgenic versus isogenic corn. J. Econ. Entomol. 90:905-909.
Palm et al. 1994. Quantification in soil of Bacillus thuringiensis var. kurstaki d
-endotoxin from transgenic plants. Molecular Ecology 3:145.
Pilcher, Obrycki, Rice and Lewis. 1997. Preimaginal development, survival and field abundance of insect predators on transgenic Bacillus thuringiensis corn. Environ. Entomol. 26:446-454.
Sanders, P.R., T.C. Lee, M.E. Groth, J.D. Astwood and R.L. Fuchs. 1998. Safety assessment of insect-protected corn. In Biotechnology and Safety Assessment, 2nd edition (Thomas, J.A., editor) Taylor and Francis, pp 241-256.
Sears, M.K., D.E. Stanley-Horn and H.R. Matilla. 2000. Preliminary report on the ecological impact of Bt corn pollen on the monarch butterfly in Ontario, submitted January 17, 2000, to Plant Biotechnology Office, Canadian Food Inspection Agency.
Wraight, C.L., A.R. Zangerl, M.J. Carroll and M.R. Berenbaum. 2000.
Absence of toxicity of Bacillus thuringiensis pollen to black swallowtails under
field conditions. Proc. Natl. Acad. Sci. USA, Vol. 97, Issue 14, 7700-7703, July
5, 2000.¹
U.S. Environmental Protection Agency, Office of Pesticide Programs,
Biopesticides and Pollution Prevention Division, Biopesticides Registration
Action Document/Preliminary Risks and Brnefits Section: Bacillus thuringiensis
Plant-Pesticides, p. IIC58.
Ibid, p. IIC52.
David S. Pimentel and Peter H. Raven, "Bt Corn Pollen Impacts on
Nontarget Lepidoptera: Assessment of Effects in Nature," PNAS 97:
8198-8199.
Ibid
Subcommittee on Basic Research of the Committee on Science, United States
House of Representatives, Seeds of Opportunity: An Assessment of the Benefits,
Safety, and Oversight of Plant Genomics and Agricultural Biotechnology, April
13, 2000, p. 43.
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