BT Pollen not so Dangerous to Monarchs

Susan Courson scourson at
Mon Feb 14 22:36:43 EST 2000

Thank you for this post.  I have been searching for information on this issue.  We
are writing a series of lessons to be used in a biotechnology workshop this summer
for secondary science teachers.

Rcjohnsen wrote:

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> NEXT >Source:           University Of Guelph (
> Contact:                Margaret Boyd , Research Communications Officer
> Phone: 519-824-4120, Ext. 2776; Email: margaret at
> Date:           Posted 2/9/2000
> New Research Suggests Bt-Corn Not Harmful To Monarch Butterfly
>    The Monarch butterfly is alive and well, despite exaggerated and misleading
> reports that biotechnology is threatening it, says a University of Guelph
> researcher.
> Field research conducted by Prof. Mark Sears, chair of the University of
> Guelph's Department of Environmental Biology and chair of the Canadian Corn
> Pest Coalition, shows pollen from Bt corn -- Bacillus thuringiensis, a
> naturally-occurring soil-borne bacterium which selectively targets specific
> groups of insects -- is not found in high enough doses on most milkweed plants
> (the food plant of the caterpillars) to hurt Monarch butterfly larvae.
>    Although Bt is harmless to humans and other animals, a U.S. study claimed
> pollen from Bt-corn damaged Monarch butterfly larvae. The study sparked a media
> frenzy and public concern about genetically modified foods.
> Sears says the U.S. study didn't demonstrate to what extent its preliminary
> findings applied to field situations. The study was completed in a lab, and the
> dosage of pollen used wasn't reported.
>    "The actual threat to the Monarch butterfly can only be determined by
> assessing the dosage that affects the larvae and their degree of exposure to
> Bt-corn pollen in the field," says Sears.
>    Sears is leading a two-year project to determine the ecological impacts of
> Bt-corn pollen on selected non-target butterfly species, including the Monarch.
> So far, studies indicate that Bt- corn is not as big a threat as
> environmentalists and the news media had anticipated.
>    "Outside of corn fields, you probably wouldn't find concentrated dosages of
> pollen because wind and rain removes it from the surface of the milkweed
> leaves," says Sears. Sears's study focused on Bt pollen and how far it travels.
> He examined milkweed stands in corn fields, at their edges, then at distances
> of five, 10 , 25, 50 and 100 metres away. He found that within the fields,
> approximately 150 pollen grains/cm2 were found on milkweed leaves. At the field
> edges, 80 to 100 grains/cm2 were found, and at five metres, only one grain/cm2
> was found. He then compared these findings to values obtained from a
> "dose-response assay" — from which data of increasing doses are plotted against
> increased mortality rates — to determine dosages with negative effects on
> Monarch butterfly larvae.
> Results show that 135 grains/cm2 — the lowest dosage he has tested on milkweed
> leaves so far and similar to that found on milkweed leaves in the field — had
> no greater effect on Monarch larvae than when they were fed non-Bt pollen.
>    "Our findings are consistent with other studies across North America," says
> Sears. "Bt- corn has always shown to be harmless to both humans and animals,
> and we now know it isn't a major threat to the Monarch butterfly."
>    Sears is being assisted by research associate Diane Stanley-Horn and
> research technician Heather Mattila from the University of Guelph, along with
> seed industry representatives and corn growers. His research is sponsored by
> the Canadian Food Inspection Agency and Environment Canada.
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