Does Bt Corn threaten any Rare Prairie Skippers
cherubini at mindspring.com
Thu Aug 24 19:05:55 EDT 2000
John Shuey wrote:
> I can give you numerous examples of regionally imperiled skippers and
> butterflies and moths that are limited to small prairie/savanna remnants that
> are completely or largely surrounded by corn alternated with beans in
> Indiana. All you have to keep in mind is that 99.9% of mesic tallgrass
> prairie has been converted to row crop agriculture - the math gives you 0.1%
> original prairie imbedded in agriculture. In most cases, rowcrop fields abut
> prairie remnants.
> And on and on... These species are all thought to occur at 10 or fewer sites
> in the state, and are certainly in danger of local extirpation. Whether or
> not Bt corn impacts these species or not - who knows - because no one has ever
> investigated the issue. The potential for negative impact to these is
> certainly present for those populations restricted to particularly small
> grassland remnants
John, do the larval food plants of any these "imperiled", "threatened" "rare"
"endangered" leps in Indiana grow within corn fields or within
a few yards of the edge of corn fields? If not, the larvae of these species will not
be exposed to harmful amounts of Bt corn pollen. By contrast, when conventional
broad spectrum insecticides or liquid formulations of Bt are aerially applied
to corn, the potential for spray drift on adjacent prairie remnants is
obviously be greater (and even this is apparently not a problem because as you
pointed out there are some "regionally imperiled" species that exist on prairie
remnants surrounded by corn)
Two other things to keep in mind here:
1. Bt corn pollen, by itself, does a poor job of controlling ANY lep pest of corn.
A Bt corn plant provides good control of only ONE moth species, the European
Corn Borer. This good control requires the larva of this moth to actually eat
the corn plant tissue (which has a far higher concentration of Bt protein)
than the pollen. No lep pest would be controlled from
exposure to the pollen alone.
2. Other lep pests of corn, such as the corn earworm moth, fall armyworm
moth, etc, are not well controlled, even though the larvae of these
moths eat the corn plant tissue and are exposed to high concentrations
of Bt protein.
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