Monarchs and the Bt Transgenic Corn Pollen Scare

[Paul Cherubini]

TV & newspaper articles are circulating around the country this week claiming a new 
farming technology may threaten the eastern monarch migration phenomenon. Is there 
substance to that concern?

Background: A seed company called Novartis supplies a genetically
modified variety of corn called Bt-corn which has genes from an
infectious bacterium (called Bt) spliced into the corn's genes, making
the corn potentially lethal to any larva of the european corn borer MOTH
which eats it. This MOTH is one of the primary pests of the Midwest corn crop. Planting 
Bt-corn provides a method of controlling (but not
eliminating) the european corn borer moth without using conventional ground or aerially 
applied insecticides. The potential problem for the monarch
butterfly comes about when pollen from the corn plants is sometimes
blown up to 200 feet away from the cornfields and lands on milkweeds
which commonly grow along the edges of corn fields. If a significant
percentage of wild monarch larvae feed on milkweeds containing seriously
harmful or lethal levels of Bt corn pollen, it could reduce the size of
the eastern monarch migration.

Cornell researchers John Losey and Linda Rayor found nearly 50% of the
monarch larvae forced to feed on milkweed dusted with an unspecified
dose of pollen from Bt-corn, in a laboratory situation, died.

Now consider the assumptions that would have to be made into order for
this Bt corn pollen to reduce the size of the eastern monarch migration
significantly; say by 25%.

The eastern fall migratory monarch migration consists (conservative
estimate) of approx. 200,000,000 butterflies. About 100,000,000 of these
(according to a recent dueterium study) are produced in a fairly narrow swath from 
Nebraska to Ohio known as the corn belt states .

To begin with, early summer monarch populations presumably would not be
impacted in the corn belt states since the corn plants aren't mature
enough to shed pollen at that time of the year. I don't know the exact
time in summer when corn sheds the pollen. Lets assume this happens at
the worst possible time: between July 20 - Aug 20 - when the monarch
larvae that produce the fall migratory adults are feeding on the
milkweed plants. To kill off 50% of these larvae, 100% of the milkweed
plants in the corn belt states would need to contain the (presumably
high) amount of pollen Cornell researchers say is lethal to 50% of
larvae forced to feed on it. By killing 50% of the 100,000,000 migratory
monarchs in the corn belt states the Bt corn pollen would have reduced
the size of the eastern monarch migration by 50,000,000 butterflies
which is 25% of the size of the eastern migration as a whole (i.e,
200,000,000 butterflies).

We must now ask how could we realistically have a situation in which
100% of the milkweed plants in the corn belt states could contain a high
enough level of Bt corn pollen in mid-late summer to kill off 50% of the
larvae feeding on those plants. The obvious answer is that we could
never have such a situation close to 100% -- or probably even 10%. Corn
is just one of several popular crops grown in the corn belt states. And
the land in the corn belt states also includes grazed and ungrazed
pastures, roadsides, parks, fallow fields, and other non-crop areas
within and along which milkweed grows.

For the sake of argument, lets make an exaggerated assumption
that 25% of the milkweed growing in the corn belt states is growing on
land within 200 feet of a corn field. Let's further assume that the
percentage of this corn planted in Bt corn rises to 75% in the near
future (presently it is at 19% and never expected to get near 100%).
With these assumptions, 0.75 times 25% = approx. 19%. So in that
scenario, 19% of the milkweed growing in the corn belt states could
potentially contain levels of Bt corn pollen in the near future that
could kill 50% of the monarch larvae present. 50% of 19% is 9.5%. So
we're talking about 9,500,000 of the 100,000,000 migratory monarchs in
the corn belt states that could potentially get killed by Bt corn
pollen.. Thats about 5% of the 200,000,000 monarchs that make up the
eastern fall migratory population--not terribly significant.

 But this 5% loss wildly ASSUMES the wind would actually carry a
sufficient amount of pollen that would reliably leave lethal residues on
milkweed plants growing within 200 feet of Bt corn fields. That seems
like an extremely unrealistic assumption considering that just one rain
would wash most pollen harmlessly into the ground. According to Terry Daynard of the 
Ontario Corn Producers Association "most pollen falls near to the corn" and "pollen is only 
available for one week in the summer" (not one month as my model above assumed). So 
this 5% potential loss might actually boil down to something less way than 1% - hardly 
something to worry about.

This analysis doesn't even consider the potential benefits to the
monarch of growing Bt corn in place of regular corn. The potential
benefit is a much reduced need to use conventional insecticides in the
corn fields in late summer to combat the european corn borer moth and the
corn rootworm beetle. This slight population benefit may completely
offset the tiny amount of larval mortality due to Bt corn pollen.

Did the Cornell scientists consider providing the media and the public
with a simple math based analysis such as the one I attempted above? Or tell reporters about 
the trivial one week period the pollen would be released? Or about the harmless fate of most 
of that pollen? No. Cornell researcher John Losey told reporters "it's certainly a serious 
potential problem" and "if it's really having an impact on a large proportion of the [monarch] 
population I think it's a very serious problem."  Then he pleaded for research funding: 
"what we need is a committment [financial] to get the data to be able to tell the
effects of genetically modified crops on the monarch population"

My conclusion is that there is no substance to the  Bt Transgenic Corn Pollen Scare. It 
disturbs me that we can't count on scientists from even top schools like Cornell to provide 
the media and the public with the full story.

Paul Cherubini, Placerville, California