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corn variety study shows no adverse effect on black swallowtail caterpillars
Barlow, Life Sciences Editor
(217) 333-5802; firstname.lastname@example.org
CHAMPAIGN, Ill. -- A Bt
corn variety grown widely in East Central Illinois in 1999 had no adverse
effect on black swallowtail caterpillars that thrive in weeds alongside
cornfields, according to both field and laboratory studies at the University
The study -- published online
Tuesday (June 6) by the Proceedings of the National Academy of Science
-- differs sharply from a May 1999 Nature report in which Cornell University
researchers, citing laboratory tests, reported that genetically modified
Bt corn slowed the growth and led to early deaths of Monarch caterpillars.
Black swallowtail larvae,
the UI researchers noted, are just as likely as are monarch caterpillars
to encounter corn pollen in the field during a key developmental time
between late June and mid-August.
"Yet under actual field
conditions, no mortality directly or indirectly attributable to ingestion
of endotoxin-containing corn pollen could be detected," they wrote.
In field tests, researchers
grew Pioneer variety 34R07, which contains Monsanto event 810 -- a particular
genetic configuration of corn carrying the gene that encodes the Bacillus
thuringiesis toxin fatal to European corn borers, which ravage corn
crops in some parts of North America. Pollen from the Bt corn was carefully
monitored and measured at a variety of locations ranging from 1/2 meter
to 7 meters from the cornfield.
"We found that many caterpillars
died, but not, as far as we could tell, due to anything connected to
the corn or the corn pollen," said May Berenbaum, head of the UI entomology
department. "There was no correlation between mortality and distance
from the cornfield or between mortality and pollen load."
Some of the deaths were directly
attributed to predation by spiders, carnivorous insects and other environmental
factors, the researchers said.
Black swallowtail females
can lay up to 800 eggs during their two-week lifetime; overall life
expectancies for caterpillars in the field invariably are low.
"We also measured the weights
of the surviving caterpillars, and we found no negative pattern suggesting
a problem in their growth and development," said UI entomologist Arthur
In the laboratory, the researchers
exposed more caterpillars to Bt corn pollen from the plants in the field,
as well as pollen from non-modified but genetically similar corn plants.
The endotoxin from the same Bt corn again had no effect on survivorship
of the caterpillars, nor did the pollen from non-modified corn.
Pollen from another transformed
variety, Novartis Max 454, however, did cause mortality in the laboratory.
Antibody assays of the Novartis event showed that it contained 40 times
as much endotoxin on average than did the 810 variety.
"This is not the green light
for all forms of genetically modified organisms," Berenbaum said. "In
this study, we examined only one GMO event -- just one genotype of Bt
corn -- in the field. This report does, however, suggest that there
are ways to reduce the risk to non-target organisms at the very least
by event selection."
The UI Environmental Council,
a campus organization devoted to environmental research, education and
service, funded the study with a grant to C. Lydia Wraight, an undergraduate
entomology student who worked with Zangerl, Berenbaum and graduate student