Home Page Link AgBioWorld Home Page
About AgBioWorld Donations Ag-Biotech News Declaration Supporting Agricultural Biotechnology Ag-biotech Info Experts on Agricultural Biotechnology Contact Links Subscribe to AgBioView Home Page

AgBioView Archives

A daily collection of news and commentaries on
ag-biotech.


Subscribe AgBioView Subscribe

Search AgBioWorld Search

AgBioView Archives

Subscribe

 


SEARCH:     

Date:

August 25, 2000

Subject:

Experts Question the New Monarch Study

 



COMMENTS ON RECENT REPORTS DEALING WITH BT CORN AND THE MONARCH BUTTERFLY

August 25, 2000, Crop Pest Ontario Vol.5 Issue 15 Mark K. Sears, Professor
and Chair, Department of Environmental Biology - University of Guelph
http://www.gov.on.ca/OMAFRA/english/crops/field/news/croppest/2000/15cpo00.htm#comments

A recent scientific paper entitled, "Field deposition of Bt transgenic
corn pollen: lethal effects on the monarch butterfly, which describes the
effect of certain Bt corn pollen deposits on milkweed leaves and its
effects on larvae of the monarch butterfly has been published online by
the journal Oecologia (August 19- See paper abstract at end of this
article). A CBS news report on the evening of August 21 followed up on
some of the issues presented in the paper. I feel it is important to
review these two presentations and comment on the nature of the
information presented.

The paper, by Laura Hansen and John Obrycki from Iowa State University,
does not constitute field research as claimed by the CBS news report. Leaf
samples of milkweed were collected from locations in or at the edge of
corn fields where pollen had been deposited naturally on the foliage.
Samples of milkweed leaves were brought to the laboratory and newly
hatched larvae of monarch butterflies were placed on leaf disks cut from
the leaves. The number of pollen grains that had been deposited on each
leaf disk were counted before being fed to individual larvae. The larvae
were allowed to feed on the leaf disks for 2 days (48 hrs), at which time
mortality of the larvae was assessed. In other experiments, pollen was
collected from the field, applied to leaves at three different doses (14,
135 and 1300 grains/cm2), small larvae fed for 48 hrs and mortality and
development and growth characteristics assessed. The studies themselves
were conducted under laboratory conditions, where temperature, lighting
and humidity were maintained to prescribed conditions. The point is, only
the collection of leaf samples with pollen and pollen itself was carried
out in the field while assessments of their effects were conducted under
controlled laboratory conditions. Field trials are those that are
conducted entirely under the conditions prevalent in the field during the
experimental period.

Because of this, the results will be affected by factors such as
predation, moisture on the leaf surfaces, variable temperature and
humidity, degradation of the pollen by sunlight, moisture, microorganisms,
rainfall, etc., effects of wind and natural dispersal of the monarch
larvae. Some or all of these factors will have a direct result on the
measurement of mortality and may completely overshadow the effects of the
Cry 1Ab toxin expressed in the pollen. True field trials are necessary to
completely understand the nature of pollen deposition on milkweed plants
and the possible effect on monarch larvae or any other species of
caterpillars.

A consistent and misleading statement by the authors and the CBS report
indicate that the results implicate all Bt corn types (or events
expressing Cry 1Ab toxin). The widespread assumption that all Bt corn
hybrids express the Cry toxin to the same degree in all tissues is
incorrect and leads to erroneous conclusions about risk to monarch
populations. The conclusions of the authors go far beyond the extent of
the data presented. In their study, only pollen from corn hybrids created
from event 176 Bt corn showed any consistent lethal effect. The effects
from consumption of pollen from Bt 11 hybrids (entirely measured in the
laboratory and with extremely small sample sizes, 10 and 16 larvae per
treatment) were inconsistent and, in the case of the highest dose tested,
not different from the control group. No sub-lethal effects were noted for
any of the treatments in the small sample of insects reared to adulthood.
In order to put these results in perspective, a wider view of the use of
Bt corn technology must be taken. Event 176 Bt corn represented about 2%
of the total Bt corn acreage planted in North America in 1999 and probably
is no more than 1% of the acreage in 2000. The authors imply in their
discussion that significant amounts of pollen could be distributed within
and up to 10m outside of corn fields such that significant mortality to
monarch larvae would occur. Their own data do not support this
speculation. Only in one instance did they record more than 135 grains/cm2
of Bt 176 pollen (the lowest toxic dose recorded), and that was from
within the field. Nowhere have they reported on the density of milkweed
plants in or around fields or in different habitats in the area, nor have
they provided any information on the phenology of the monarch populations
in relation to the pollen shed period of the Bt corn hybrids. Without this
information, it is entirely improper to speculate on the risk associated
with the Cry 1Ab toxin found in some Bt corn hybrids. Therefore, the
results of these experiments cannot possibly represent the potential
impact of Bt pollen from all events, as the authors suggest, across the
extensive range of the monarch butterfly in North America. In fact, the
combined impacts of destruction of overwintering habitat of the butterfly
in Mexico, herbicide use and mowing that eliminates milkweed stands in and
around field crops, and even mortality to migrating monarch butterflies by
collisions with vehicles are far more likely to impact on monarch
populations than the tiny fraction of Bt corn acreage that may deposit
sufficient pollen to the extent that some larvae will be effected. In
fact, the latest reports from Monarch Watch, an organization that has
documented the changes in monarch butterfly populations in North America
for a number of years, have indicated that populations of this insect are
on the increase in the past few years.

This in the face of speculation that monarch populations are under severe
threat due to the increased acreage of Bt corn as this new technology
becomes more widely accepted.
--
Dr. Sears Can Be Contacted At:
Mark K. Sears
Professor and Chair
Department of Environmental Biology
University of Guelph
Guelph, Ontario
N1G 2W1
msears@evbhort.uoguelph.ca
--
*Oecologia(http://link.springer.de/link/service/journals/00442/contents/00/0 0502/s004420000502ch002.html
-----------------------------------

HERE WE GO AGAIN: BT CORN AND MONARCH BUTTERFLIES

August 25, 2000 Pest Management and Crop Development Kevin Steffey, editor
http://www.ag.uiuc.edu/cespubs/pest/articles/200021d.html

CBS Evening News aired yet another story about Bt corn and monarch
butterflies on Monday, August 21. By Tuesday and Wednesday of that week,
the Web was filled with related stories, including points and
counterpoints, punches and counterpunches, pros and cons. The furor this
time was generated from an article published electronically for the
journal Oecologia by Laura C. Hansen Jesse and John J. Obrycki at Iowa
State University. The title of the article is "Field Deposition of Bt
Transgenic Corn Pollen: Lethal Effects on the Monarch Butterfly," and you
can find it on the Web at
http://link.springer.de/link/service/journals/00442/contents/. Click on
"Article in HTML" to get the complete article, with tables, figures, and
references in separate windows. Following is the abstract of the paper:
"We present the first evidence that transgenic Bacillus thuringiensis (Bt)
corn pollen naturally deposited on Asclepias syriaca; common milkweed, in
a corn field causes significant mortality of Danaus plexippus L.
(Lepidoptera: Danaidae) larvae. Larvae feeding for 48 h on A. syriaca
plants naturally dusted with pollen from Bt corn plants suffered
significantly higher rates of mortality at 48 h (20±3%) compared to larvae
feeding on leaves with no pollen (3±3%), or feeding on leaves with non-Bt
pollen (0%). Mortality at 120 h of D. plexippus larvae exposed to 135
pollen grains/cm2 of transgenic pollen for 48 h ranged from 37 to 70%. We
found no sub-lethal effects on D. plexippus adults reared from larvae that
survived a 48-h exposure to three concentrations of Bt pollen. Based on
our quantification of the wind dispersal of this pollen beyond the edges
of agricultural fields, we predict that the effects of transgenic pollen
on D. plexippus may be observed at least 10 m from transgenic field
borders. However, the highest larval mortality will likely occur on A.
syriaca plants in corn fields or within 3 m of the edge of a transgenic
corn field. We conclude that the ecological effects of transgenic
insecticidal crops need to be evaluated more fully before they are planted
over extensive areas." Dr. Val Giddings, Vice President for Food and
Agriculture of the Biotechnology Industry Organization (BIO), issued the
following statement in response: "Dr. Obrycki’s research stands in the
shadow of more than 20 independent studies by widely recognized scientific
experts who have found that Bacillus thuringiensis (Bt) corn does not pose
a significant risk to the monarch butterfly. This report considers only
one small area of this complex topic and the conclusions put forward by
the authors stand in stark contrast to those of the broader scientific
community’s research. The Oecologia paper is not truly ‘field research’
inasmuch as much of what it reports is based on analyses taking place in
laboratory manipulations rather than field conditions. Furthermore, the
paper clearly shows that larval mortality was not correlated with the
number of pollen grains on the plant or the plant location within or at
the edge of the field, surprises in search of an explanation. Both the
United States Environmental Protection Agency and the Department of
Agriculture have studied Bt corn for many years. Just last week the EPA
extended the registrations of these products through the 2001 growing
season. And in April, the EPA dismissed a Greenpeace lawsuit challenging
the Bt plant registrations on a lack of merit, and stated ‘. . . available
scientific data and information indicates that the cultivation of Bt crops
has a positive ecological effect, when compared to the most likely
alternatives.’ To imply that Bt corn has a negative effect on monarch
butterflies flies in the face of the fact that last year, more than 28
million acres were planted with Bt corn, an increase of approximately 40%
over the previous year. In the same time period, the monarch butterfly
population flourished and increased by about 30%, according to Monarch
Watch."

There you have it, point and counterpoint.

I read the Oecologia article carefully, and the study reported was most
definitely not what I would consider a field study. I fact, I’ve read that
it has been referred to as a "modified field study." Although the corn and
milkweed plants initially were grown outside in relatively small plots,
the mortality information generated w as from first-instar monarch
caterpillars feeding on milkweed leaf disks (with different amounts of Bt
and non-Bt corn pollen) in the laboratory. Another critical point is that
although pollen deposition was measured from two types of Bt corn (from
event 176 and event Bt11), mortality of monarch caterpillars exposed to
field-d epositedpollen was measured only for event 176 Bt corn. Less Bt
toxin is expressed in event Bt11 pollen than in event 176 pollen. In
addition, most of the Bt corn grown in the United States is from event
MON810, an event very similar to event Bt11. The comparative amounts of Bt
toxin in events 176 and MON810 are 7.1 micrograms and 0.9 micrograms Bt
toxin/g fresh weight of pollen, respectively. Furthermore, the contrived
density of 135 pollen grains/cm2 was considerably higher than the mean
densities of pollen grains measured on milkweed plants 0.2, 1, 3, 5, and
10 meters from the edge of the Bt corn. Quite frankly, I’m getting tired
of the press making an issue out of scientific findings that don’t
describe the real world very well. I also am dismayed by some of the
sweeping conclusions the authors of the Oecologia article made in
reference to the potential effects of Bt corn pollen on monarch
butterflies in the real world. I will not argue with the assertion that
potential limitations of Bt corn and other transgenic crops need to be
studied. However, I am disgusted with the misrepresentation of some
scientific findings and the accompanying hyperbole engendered by some of
the media. If scientific evidence reveals negative impacts of transgenic
crops, then let the chips fall where they may. But let’s be very careful
about interpretations of scientific studies.


UNIV. OF ILLINOIS ENTOMOLOGIST: LATEST BT CORN/MONARCH STUDY NOT A TRUE
FIELD STUDY
August 25, 2000 AgWeb Julianne Johnston
http://www.agweb.com/news/news.cfm?id=10857&breakingnews=1&pf=1

This week’s study done by two Iowa State University entomologists on the
effects of Bt corn on Monarch butterflies has certainly garnered a lot of
press. After carefully reviewing what the ISU researchers referred to as a
"field study of Bt corn pollen" and the "lethal effects on the Monarch
butterfly," University of Illinois entomologist Kevin Steffey says he
would not consider the work as a "true field study." Steffey says he’s
seen the work referred to as a "modified field study." In making his
point, Steffey says that while corn and milkweed plants initially were
grown outside in relatively small plots, the mortality information
generated was from first-instar monarch caterpillars feeding on milkweed
leaf disks - with different amounts of Bt and non-Bt corn pollen - in the
laboratory.

"Another critical point is that although pollen deposition was measured
from two types of Bt corn (from event 176 and event Bt11), mortality of
monarch caterpillars exposed to field-deposited pollen was measured only
for event 176 Bt corn," points out Steffey in the latest issue of the U of
I Pest Management and Crop Development Bulletin. "Less Bt toxin is
expressed in event Bt11 pollen than in event 176 pollen."

Steffey also points out that most of the Bt corn grown in the United
States is a Monsanto variety, although similar to what the ISU researchers
referred to as event Bt11. "The comparative amounts of Bt toxin in events
176 and MON810 are 7.1 micrograms and 0.9 micrograms Bt toxin/g fresh
weight of pollen, respectively," says Steffey. "Furthermore, the contrived
density of 135 pollen grains/cm2 was considerably higher than the mean
densities of pollen grains measured on milkweed plants 0.2, 1, 3, 5, and
10 meters from the edge of the Bt corn." Steffey openly admits he’s
getting tired of the press making an issue out of scientific findings
"that don’t describe the real world very well." He also said he is
concerned by the conclusions of the ISU study, which made reference to the
potential effects of Bt corn pollen on Monarch butterflies in the real
world. "I will not argue with the assertion that potential limitations of
Bt corn and other transgenic crops need to be studied," he said. "However,
I am disgusted with the misrepresentation of some scientific findings and
the accompanying hyperbole engendered by some of the media."

"If scientific evidence reveals negative impacts of transgenic crops, then
let the chips fall where they may. But let’s be very careful about
interpretations of scientific studies," urged Steffey