Monarchs & Bt corn issue update

Pierre Zagatti zagatti at
Fri Jun 18 04:14:42 EDT 1999

Paul Cherubini wrote:

> (many true arguments from the Biotechnology Industry Organization)

I just received a complete report from Monsanto about this topic,
which has already raised some discussion in this list/ng. I guess they
(Monsanto) think I'll be designed as an expert to identify the real
problems for French Authorities, but I did'nt receive anything yet.

Having carefully read all this stuff, I think that two important points have been missed
by either companies or opponents to GM Bt corn:

First - The toxicity of Bt toxin (namely Cry1A(b)) is variable among species. It has been
studied for various lepidoptera that are pests of corn, but not (at my knowledge) for
non target lepidoptera. We might expect a stronger susceptibility to Bt toxin in
non-pest species, since their genetic adaptability is usually lower than in pests.
The monarch is certainly a very bad example, because it feeds on a highly toxic
plant family thus developed very efficient detoxication mechanisms.

Second - The effects of toxin on monarch larvae (and others) are expressed in terms
of acute toxicity (i.e. LD 50). We don't know the effects of sublethal doses on
sexual behavior of adults or general ability to survive and produce offspring.
Several examples of sublethal effects have already shown the importance of this
phenomenon: - neurotoxic pyrethroids evoke hyperactivity in kestrel falcons
which leads to the death of the chicks, - expression of protease inhibitors in
GM oilseed rape disrupts the foraging behavior of pollinating honeybees.

My conclusion is that more studies are needed on non target species.
The models should be vulnerable species that might feed at vicinity
of corn fields, and the study should consider both acute toxicity
and effects of sublethal doses on population survival.

INRA Unite de Phytopharmacie et Mediateurs Chimiques
78026 Versailles Cedex
Tel: (33) 1 30 83 31 18
e-mail zagatti at

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