Monarch butterfly larvae exposed to anthers from Bt maize ate
less and gained less weight.
Maize (Zea mays L.).
Inserted Transgene and Intended Effect:
crylAb gene derived from Bacillus thuringiensis
(Bt). This gene gives transgenic Bt maize (also called
Bt corn) the ability to produce insecticidal delta-endotoxin that
can kill the larvae of the European corn borer and other insect pests
feeding on the corn.
Goal of This Study:
Investigate how Bt maize may affect a non-target insect, the larva of the
monarch butterfly (Danaus plexippus). In a laboratory experiment,
monarch butterfly larvae were raised in Petri dishes containing the
leaves of common milkweed; some dishes contained, in addition, either
anthers from Bt corn or anthers from unmanipulated corn.
Results of This Study:
"Larvae exposed to Bt anthers fed less and gained less weight
than larvae exposed to non-Bt or no anthers, yet there was no evidence of
feeding on anthers" (p. 228). That they fed less and gained less weight
was not because the larvae moved around more.
The authors conclude that their "results suggest that larvae exposed to
Bt anthers behave differently and that ingestion may not be the only way
Bt can affect nontarget insects like the monarch butterfly" (p. 228). They
do not know what might be causing this change in feeding behavior.
An initial laboratory study by Losey et al. indicated that Bt corn
pollen can harm Monarch butterfly larvae (Losey, J. E., L. S. Rayor,
and M. E. Carter (1999). "Transgenic Pollen Harms Monarch Larvae,"
Nature vol. 399, p. 214). This study received widespread
attention and particularly careful scrutiny by other scientists. In
a collaborative effort, a group of scientists including the USDA's
R. Hellmich, who is a co-author of the study reported here, carried
out studies that were published in 2001 and can be accessed at
http://www.ars.usda.gov/is/br/btcorn/. These studies indicated, on the
whole, that there may be little risk to Monarch larvae in the wild due
to feeding on Bt maize pollen. The study reported here shows that
the issue is not yet resolved.
Prasifka, P. L., R. Hellmich, J. Prasifka, and L. Lewis (2007). "Effects
of CrylAb-Expressing Corn Anthers on the Movement of Monarch Butterfly
Larvae," Environmental Entomology vol. 36, pp. 228-33.
Department of Entomology, Iowa State University, and the USDA-ERS,
Corn Insects and Crop Genetics Research Unit.
Grants from the USDA-ERS, U.S. Environmental Protection Agency, and
Agricultural Biotechnology Stewardship Technical Committee.
Commercialized crop, Monsanto's Bt maize (MON810).
Copyright 2008 The Nature