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NON-TARGET
EFFECTS OF BT CORN POLLEN ON THE MONARCH BUTTERFLY (LEPIDOPTERA:
DANAIDAE)
*L.
Hansen, Iowa State University, Ames , IA 50011 and J. Obrycki,
Iowa State University, Ames, IA 50011 Contact e-mail: lrahnsen@iastate.edu
The expression and dispersal of Bt toxin in the pollen
from transgenic crop plants may pose a risk to non-target
Lepidopterans. When Bt corn pollen lands on the leaves of
plants in and around corn fields, it exposes non-target
Lepidopteran larvae feeding on these plants to Bt toxins.
In Iowa, where the landscape is dominated by row-crop agriculture,
areas effected could include a significant portion of non-cultivated
areas, including remnant prairies, roadside ditches and
wetlands. The monarch, Danaus plexippus (Lepidoptera: Danaidae)
was chosen as the non-target Lepidopteran species for this
study because it is a common butterfly species that feeds
on several species of milkweed, Asclepias. Asclepias syriaca
(Asclepiadaceae) commonly grows in road ditches, grassy
areas between fields, and within corn fields, so it is likely
to have Bt corn pollen deposited upon it. The first step
of this study was to determine the amount of corn pollen
deposited on A. syriaca leaves within and adjacent to a
Bt corn field at 0 m, 1m, and 3m. The highest levels of
pollen deposition was found on plants within the corn field,
and lowest levels found at three meters from the edge of
the corn field. Leaf samples taken from within and at the
edge of the corn field were used to assess mortality of
first instar monarch, D. plexippus exposed Bt and non-Bt
corn pollen. Within 48 hours, there was 19% mortality in
the Bt corn pollen treatment compared to 0% on non-Bt corn
pollen exposed plants and 3% in the no pollen controls.
Hansen, L. C. & J. J. Obrycki.
1999. Poster presentation at the North Central Entomology
Society of America Meeting , Des Moines, Iowa.
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