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Butterfly Researchers Urge Caution in Over-Interpreting Results

Academic Researchers and Industry Associations Agree Reports on Bt
Crop Impact on Monarch Butterflies Overblown

WASHINGTON, D.C. (June 10, 1999) – Several academic experts have urged
caution when interpreting the results of a preliminary laboratory study at
Cornell university on the effect of Bt corn pollen on the Monarch
butterfly that was published as a letter in the journal Nature (5/20/99).
These university researchers stressed that the monarch study did not
represent natural conditions and that extensive environmental research has
confirmed the safety of Bt corn on non-target insects, such as the
ladybird beetle, honeybee and the green lacewing, in the natural

Dr. John Losey, the Cornell University entomology professor who
conducted the research said, “Our study was conducted in the laboratory
and, while it raises an important issue, it would be inappropriate to draw
any conclusions about the risk to monarch populations in the field based
solely on these initial result.”

In a response letter published in Nature (6/3/99), Dr. John Beringer,
professor at the University of Bristol’s School of Biological Science in
the United Kingdom and chairman of the U.K. Advisory Committee on Releases
to the Environment, wrote, “There is a need for scientific rigour in the
presentation of the information to ensure that it is not misrepresented
… preliminary observations should not be over-interpreted”.

We want to make sure that the monarch is protect, and we want to verify
the belief of numerous scientists that Bt pollen is not putting the
monarchs at significant risk,” said Dr. L. Val Giddings, vice president
for food and agriculture, Biotechnology Industry Organization (BIO).

Factors in field reduce likelihood of monarch exposure to corn

By design, the Cornell researchers did not match the conditions that
would be present in a natural setting. In the laboratory, the caterpillars
were given no choice but to feed on one treatment, in this case leaves
dusted with corn pollen. In the field, the caterpillars may move about and
may avoid ingesting pollen.

Under natural conditions, monarch larvae feed primarily on milkweed.
Most researchers consider it likely that most milkweed does not grow close
enough to corn fields to be exposed to significant amounts of corn pollen.
According to an Iowa State University study by Laura Hansen and Dr. John
Obrycki, the majority of corn pollen stays within the cornfield in a
natural setting. The Iowa State study found that pollen density decreases
by 70 percent a the edge of a cornfield, and by 90 percent three meters
away from the edge of the cornfield.

Further, the majority of monarch larvae feed on milkweed when corn
pollen is not present. Corn plants producer or “shed” pollen for a short
period of time (typically most pollen is produced in a given field over a
5-10 day period.) Based on known migration behavior, even in those regions
in which corn and monarchs co-habitate, only a small portion of the
monarch population will be present when corn is shedding pollen.

For these reasons – – the location of milkweed outside the range of
most pollen drift, and minimal overlap between monarch feeding and pollen
shedding – it is likely that the vast majority of monarch larvae
throughout their range over a growing season are never exposed to corn
pollen in nature at all.

Bt Corn Benefits Non-target Insects

The Bt corn crops that are currently on the market were developed to
control the European Corn Borer. Prior to the introduction of Bt corn,
farmers controlled European Corn Borer with conventional insecticide
sprays that are toxic to monarch butterfly larvae and other desirable,
non-target species. By reducing the use of these insecticides, Bt corn
reduces the potential to harm non-target species, and reduces impacts of
agricultural inputs on the environment in general.

“I still think the proven benefits of Bt corn outweigh the potential
risk,” stated Dr. Losey. “We can’t forget that Bt corn and other
transgenic crops have a huge potential for reducing pesticide use and
increasing yields.”

Dr. Chris DiFonzo, Michigan State University Field Crops Entomologist
& Pesticide Education Coordinator, said “Bt corn is a much safer
method of pest management, and has less detrimental impact on all aspects
of the environment — monarch included — than the use of broad-spectrum

“When you consider the monarch butterflies in context with the widely
recognized benefits of Bt crops, it’s clear that trends in agriculture
will only help the monarchs and the environment overall, said BIO’s Val
Giddings, “For example, Bt crops preserve beneficial insects that prey on
harmful insect pests, thus limiting the need for additional insecticide
sprays. Growers planting Bt crops have dramatically reduced the damage
done by harmful pests and have reduced handling and exposure of
insecticides on the farm.”

“As conservation groups have noted, the primary threat to the monarch
butterfly is the loss of crucial winter habitat in southern California and
central Mexico,” Giddings added. “Other threats come from habitat
degradation along butterfly migratory routes, pesticides, and other human
activities. It’s not an exaggeration to say more monarchs succumb to
high-velocity collisions with car windshields than ever encounter corn

In addition to the extensive number of field studies that have been
conducted to determine the effect of Bt crops on beneficial insects, BIO
and the American Crop Protection Association are working along with
industry partners to address and evaluate these issues further. The
available information strongly supports the advantages of Bt crops on
beneficial insect population relative to the use of insecticides.

For further information on this subject, contact the following
independent experts:

Warren Stevens, Ph.D
Missouri Botanical Garden
4344 Shaw Blvd,
St. Louis, MO 63110-2291
(314) 577-5103

Albert Tenuta, Ph.D.
Pest Management Specialist and Plant
Ontario Ministry of Agriculture, Food and Rural
Ridgetown Campus, University of Guelph


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