Study: Biotech Corn Kills Monarch

Paul Cherubini cherubini at
Wed Aug 23 21:45:55 EDT 2000

Clay Taylor wrote:
> Paul - how much of that $100,000 spent by "the industry" actually
> went into the field studies?  In light of the potential gains "the industry"
> stands to make from such a study, only spending $100K seems to be a pretty
> small investment.  How thorough were their methods in investigating the
> differences you point out between laboratory Vs. field testing of Monarchs
> and Bt corn?

Below are the results that were gained from the $100,000+ worth of
biotech industry funded studies conducted last summer.
These results were copied and pasted from the following website:


Milkweed density is highest in roadsides. 
Dr. Doug Buhler, research agronomist at the USDA-ARS, and Dr. Robert
Hartzler, associate professor and Extension weed scientist in the Agronomy 
Department at Iowa State University found that Iowa roadsides had 48
common milkweed patches per hectare, while corn and soybean
fields had only seven patches per hectare. They concluded that common 
milkweed in roadsides may be especially important to monarchs due to
the frequent occurrence of milkweed in roadsides and
the uniform distribution of roadsides across the landscape. In another 
survey, Hartzler and Buhler also found that the majority of milkweeds
along roadsides were distant from field edges. Milkweed density was 
approximately twice as high adjacent to the road (186 patches per hectare) 
and in the center of the roadside (165 patches per hectare) as it was next to
the field edge (89 patches per hectare). 

About 50 percent of corn and soybean fields were reported to have some 
milkweed present, although usually appearing in small patches. Because 
the plants can be poisonous to livestock and compete with crops for sunlight,
nutrients and water, farmers try to eliminate milkweeds from
fields with the use of crop rotations, plowing, disking and herbicides. 


Researchers from several universities and industry surveyed the occurrence
of milkweeds along roadsides in Iowa, Nebraska, Illinois, Indiana and
Maryland. Dr. David Isenhour, entomologist for Monsanto Company, 
reported that survey results showed from 15 to 41 percent of roadside
milkweeds were adjacent to cornfields. In addition, the Iowa surveyors 
found only 19 percent of roadside milkweeds occurred within 1 to 3 
meters of the field edge. Considering both proximity
and location, less than 8 percent of roadside milkweeds were found
to be exposed to meaningful amounts of pollen. 


Tests by Dr. John Losey, Cornell University assistant professor of 
entomology, show that monarchs avoid laying eggs on milkweed 
surrounded by corn. Losey placed potted milkweeds by themselves 
or surrounded by corn plants and found that monarch adults preferred 
to lay eggs on milkweeds in the open. If this is typical behavior for 
monarchs in natural environments, then larvae would be less common
on milkweeds very close to cornfields. 

When given a choice between feeding on milkweed leaves with no 
pollen or high levels of Bt pollen, the majority of monarch larvae 
chose no pollen, reported researchers from
USDA-Agricultural Research Service (ARS) and Iowa State University. 


Scientists acknowledge that exposure to Bt pollen varies from region 
to region. Dr. Galen Dively, pest management specialist and professor
of entomology at the University of Maryland, monitored Maryland 
cornfields and monarch development in 1999. He found that corn plants
had completed pollen shed before monarch caterpillars were first 
observed feeding on milkweed. 

Dively saw adult butterflies during the short period of pollen shed,
but since they feed on plant nectar, not pollen, they are not affected 
by Bt corn. Similarly, Dr. John Foster, professor of
entomology at the University of Nebraska, observed that by late
July, corn pollination in Nebraska was 95 percent complete before
monarch eggs were observed on milkweeds in the vicinity of corn. 
He added that rain, dew and irrigation all tend to wash off the pollen. 

Pennsylvania State University researchers, using computer models 
and historical climatic information, found that a more mixed picture 
should be expected across the entire region of monarch migration. 
Dr. Dennis Calvin, associate professor of entomology at Penn State,
reported very little overlap of pollen shed in the early larval stages in
Pennsylvania and greater overlap in the late larval stages and as adults.
Calvin and his colleagues will continue to examine when and
to what extent pollen shed may overlap monarch development, but 
he expects that overlap will vary greatly. 


Corn pollen doesn¹t travel far. Due to its large particle size (90 to
100 microns), most corn pollen deposits stay within the
cornfield, said Dr. Stuart Weiss of Stanford University. He noted 
that at wind speeds of 5 meters per second (11 miles per hour) or less, 
most pollen grains fall close to the field edge. 

The volume of pollen falls off sharply just a few feet away from
cornfields, reported Dr. Mark Sears, chair of the University of Guelph¹s 
Department of Environmental Biology. Using pollen traps set on poles 
about the height of milkweed, Sears and his colleagues determined that 90
percent of pollen grains traveled less than 5 meters (16.5 feet) from the 
field edge. Because pollen density dropped off rapidly a short distance
from the field edge, ³The risk to monarch larvae is very minimal,² he said. 

Likewise, Dively also set out to measure how much pollen lands on 
milkweed leaves in and around Maryland cornfields. He, too, found the
pollen drops off rapidly beyond the field edge. He reported that pollen levels
on milkweed within the field at the end of full pollination run between
200 and 250 pollen grains per square centimeter. Going outside the field, 
within the first 3 meters (10 feet), the pollen level drops 90 percent ­ to 
20 to 30 grains per square centimeter.

Milkweed leaves capture only 30 percent of available pollen, reported 
Dr. John Pleasants, professor in the Department of Zoology and Genetics 
at Iowa State University. Wind speed and direction also affect pollen 
deposition, as illustrated in Figure 6, which shows an Iowa field that
experienced prevailing winds from the south. Like his colleagues, 
Pleasants found the pollen levels decrease rapidly going away from 
the field edge and that uncommonly ³high² pollen
densities (150 grains per square centimeter) were not found on milkweeds
just 2 meters (6.6 feet) from a Bt cornfield. 

Typical pollen levels had little to no effect 
Different types of Bt corn pollen seem to have varying degrees of toxicity, 
Iowa State University and USDA researchers reported. Feeding trials with
monarch larvae and two types of Bt pollen ­
YieldGard (MON810) and StarLink (CBH351) ­ indicated that leaves with 
high pollen densities of 150 grains per square centimeter had no effect on
larval weight or survivorship. Pleasants and Dr.
Richard Hellmich showed that pollen densities dropped to harmless levels 
beyond 1 meter (3 feet) from the edge of the field. Thus, the potential effects
on monarch caterpillars that may be present very near to pollinating corn would 
be limited. However, KnockOut and NatureGard varieties (Event 176), 
which represents just 2.5 percent of Bt corn, was more toxic, with higher 
mortality rates and lower weight gains. 

University of Nebraska professor of entomology Dr. Blair Siegfried performed
a feeding study in which young caterpillars were administered various 
concentrations of purified Bt proteins in an artificial diet. The caterpillars were
more sensitive to some proteins and less sensitive to others. At
high concentrations of the most toxic Bt protein, the larvae all died. 
At moderate concentrations, inhibited growth was observed. 

These findings are no surprise since the original Nature article already 
demonstrated toxicity in lab conditions when caterpillars consumed large 
amounts of the most toxic Bt protein. Again, the
question at hand is how toxicity and exposure work together to determine 
risk in a real-world situation.

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