[NAFEX] Bt toxin [SEC=UNCLASSIFIED]

ADAMSON, Karl Karl.Adamson at apvma.gov.au
Fri Jun 19 01:22:53 EDT 2009


Donna, I think there is some confusion here.

The way BT is made is that you grow the bacteria in a big vat to the
point where it exhausts its food supply.  At this point it is forced by
starvation to produce dormant spores.  It is these dormant spores that
contain the crystalline BT toxin. Technically an endotoxin as it is only
release when the organism is destroyed. This concentrate of spores is
then diluted with a few things and sold as the final product.

So it is the living organism (in its resting state) that is being sold.
However, in reality, it is not the living organism that is responsible
for killing the insect.  When a spore enters an alkaline insect gut it
starts to be digested and the toxin is released due to this digestion
process.  The spore is no longer viable.

This toxin binds to specific receptors in the guy wall and, like a
rabbit trap in reverse, springs open to rip a hole in the gut wall.  To
an insect its quite nasty stuff and the insect dies from what is
effectively many gastric ulcers.

While not unheard of, it is very rare for the spores to germinate and
reproduce in insects.  This is a very different mode of action to other
common bioorganisims which are used to control insects such as nuclear
polyhedral viruses (NPV), metarhyzium or bovaria. All of which are
deployed as dormant stages, but which then germinate, reproduce and
incidentally kill their insect hosts.  This, unlike BT, leads to a
prolonging of the organisims activity in the field.

Now, for those concerned with my descriptions, according to modern
animal ethicists neither bacteria nor insects feel pain. So the
starvation, nor the slow death associated from a leaky gut cannot be
considered as cruel.

Karl

Donna Wrote:
>Yes, like Kevin, I have only seen the organism for sale.  You spray in
on crops typically attacked by caterpillars, the >caterpillars eat the
bacteria, the organism grows producing a toxin, the caterpillar stops
eating within 24 hours and
>dies, leaving behind a corpse well laden with more of the Bt bacteria
to continue the cycle.  That's one of the really
>weird things about Bt corn, that it's a whole field full of plants
producing Bt toxin, instead of a few caterpillars 
>scattered here and there.  No one knows what all that Bt toxin can do.
Donna


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