Web Page Available on Bt Corn Risk to Monarch Butterflies

[SFleischak at aol.com]

From: "ARS News Service" <isnv at ars-grin.gov>
To: "ARS News List" <ars-news at ars-grin.gov>
Subject: Web Page Available on Bt Corn Risk to Monarch Butterflies
Date: Tue, Oct 9, 2001, 8:02 AM


STORY LEAD:
Web Page Available on Bt Corn Risk to Monarch Butterflies

___________________________________________

ARS News Service
Agricultural Research Service, USDA
Kim Kaplan, (301) 504-1637, Kaplan at ars.usda.gov
October 5, 2001
___________________________________________

Information about Bt corn's impact on monarch butterflies is now available
on a web page (www.ars.usda.gov/is/br/btcorn) from the Agricultural Research
Service. The core of the web page is research coordinated by ARS and
recently published in the Proceedings of the National Academy of Sciences.

That Bt corn might present a risk became a matter of scientific and public
concern when a small study in 1999 indicated caterpillars suffered when
given no choice but to feed on milkweed leaves heavily dusted with Bt corn
pollen. Bacillus thuringiensis (Bt) is a soil bacterium used as an effective
alternative to chemical insecticides for controlling moth pests.

Two major questions needed to be scientifically answered to establish
whether Bt corn actually posed a threat to monarch caterpillars--the direct
toxicity of Bt pollen for caterpillars and the likelihood that caterpillars
might be exposed to that much pollen, according to entomologist Richard L.
Hellmich with the ARS Corn Insects and Crops Genetics Research Unit in Ames,
Iowa. (http://cicgr.agron.iastate.edu/CICGR/home.html)

The studies found monarch caterpillars are not very sensitive to pollen from
most types of Bt corn, and that caterpillar exposure to Bt pollen is low. It
took pollen levels greater than 1,000 grains of pollen per square centimeter
(cm2) before there were any toxic effects in monarch caterpillars, and even
greater levels before the effect was significant.

Caterpillars were found on milkweed in cornfields during the 1-2 weeks
pollen is shed by corn, but corn pollen levels on these plants were found to
average only about 170 pollen grains per cm2. Less than 1 percent of the
milkweed leaves in cornfields had pollen levels exceeding 1000 grains per
cm2 during pollen shed.

One variety of Bt corn--Bt 176--did have a toxic effect with pollen doses as
small as 10 pollen grains per cm2. Bt 176 is one of the earliest forms of Bt
corn and has never been planted on more than 2 percent of the corn acres. It
will be completely phased out by 2003.

ARS is the U.S. Department of Agriculture's chief scientific research
agency.

 
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