Bt corn flap

Neil Jones Neil at
Sun Apr 2 17:51:49 EDT 2000

In article <38e46ac0.5731870 at>
           r.knell at "Rob Knell" writes:

> On Wed, 29 Mar 00 22:34:42 GMT, Neil at (Neil Jones)
> wrote:
> >In article <38e25a3b.108978 at>
> >           robnpam at "Rob and Pam" writes:
> >
> >> On Wed, 29 Mar 00 14:14:10 GMT, Neil at (Neil Jones)
> >> wrote:
> >> 
> >> >
> >> >The so called Toxin expressed in the BT corn is NOT identical to that
> >> >produced in organic control agents. 
> >> 
> >> Well, it's the delta-endotoxin gene from Bt var kurstaki, which is the
> >> strain used for lepidoptera control. How about this : The toxin (and
> >> it is a toxin, see later) expressed in Bt corn is identical to the
> >> major component of the toxin produced in one of the commonest organic
> >> control agents.
> >
> >But not the entire component. The natural product contains variants. These
> >help to prevent resistance taking hold.
> >
> I'm not sure what you're describing as the 'natural product' here. If
> you're saying that the Bt preparations used by organic growers for
> control have increased variability which helps control resistance,
> then I must disagree with you: these products are single strains of Bt
> and will induce resistance in much the same way as GM plants.

NO this is not what I am saying. My understanding is that Bacillus thurigiensis
naturally produces variants within the same bacterial cell.

> you're saying that the population of Bt in the wild is variable, then
> you're correct, but that isn't very relevant to pest control as it's
> done at the moment.
> >> 
> >> >Bacillus thurigiensis is a specialised
> >> >bacerial predator of invertebrates.
> >> 
> >> We don't know too much about the 'normal' ecological niche for Bt but
> >> it seems to be a bacterium that lives as a conventional saprophyte a
> >> lot of the time and only occasionally kills insects. It's certainly
> >> not an obligate specialised predator.
> >
> >This is worrying. We don't know what this organism does but it is OK
> >to incorporate its ecologically active characteristics in other
> >organisms.
> Or why not put it another way. We don't know what this organism does,
> so surely it's better to use just a single protein from it. We know
> exactly what effect this protein has, and if we engineer it into our
> crop plants then the control agent is targeted directly to where it's
> needed most.

This is where a lot of the criticism of the GM industry comes in.
"We know what this gene does in an organism therefore it is safe"
The ecological effects of an organism bearing a gene are very difficult
to establish. This new Bt gene is not confined to the plant it is being
blown around in the air with pollen. All the furore over the monarch butterfly
demonstrated that more research needed to be done. 
Of course it gets worse the more genes are added or fiddled with.

 Is this not a more environmentally friendly procedure
> than just spraying the live organism around, killing non-target
> organisms willy-nilly and running the risk that it will prove to do
> something we hadn't predicted, or even worse using broad spectrum
> chemical pesiticides?

I am not a supporter of BT use in organic agriculture.

> I'm not saying that you're wrong, just that the argument can be turned
> around 180 degrees and have just as much validity.
> >Secondly, it may well be able to survive and grow without lepidoptera but
> >it does not have this gene by accident.
> >It is an intricate and specialised molecule that fits like a key in a lock.
> >What is more it only fits this lock once it has been partially digested by the
> >caterpillar. Variants of this gene exist that do this in a variety of
> >other organisms. This did not happen by accident. It has obviously evolved
> >for this purpose. If the organism that produces this precisely formed protein
> >in quantity does not have a use for it then selection would soon
> >weed out those organisms that wasted energy producing it.
> >
> Yes indeed. Nonetheless, the protein is only expressed when the
> bacterium sporulates, and if it only sporulates rarely then selection
> will not be that great.

These are not newly evoloved organisms there will have been plenty of time
for evolution to have worked. Indeed I would have thought that the construction
of spores that worked well to have been the subject of particularly intensive

> >The truth is that very very little research is done on the role of pathogens
> >in the ecology of non-pest lepidoptera.
> >
> Speaking as someone who works, among other things, on the ecology of
> pathogens of lepidoptera, I would disagree with you here. There is a
> great deal of research done on the role of pathogens in the ecology of
> lepidoptera, and the reason that most of this is done on pest insects
> is because they're easy to get hold of and usually much easier to rear
> in the lab than non-pests. Many of the conclusions that are reached by
> working with pest leps are equally applicable to non-pest species,
> it's just that a lot of non-pest species are a right pain to work
> with. 

Well I really think this is not valid. I have searched for information
on this. One one recent occasion I went through 125 volumes of abstract journals
just looking for references. (The one on  P. homerus  I
 encountered beforehand. I would have noted it but I wasn't particularly 
interested in BT at the time.) All the work is on pest species. Pest species
have a very different ecology and are far less vulerable to any kind of
external influence. The small (cabbage) white (Pieris rapae) for example has
got established all over the world, but if you look at the research at establishing new
populations of most non-pest species of butterfly in the UK the results are
very poor. In fact for most species it does not work at all!
(I wonder if I'll get flamed again for saying that but it is all well

> >I don't recall a reference I read it recently whilst browsing through
> >a journal but I would guess a search on P. homerus would find it.
> >
> Couldn't find it on BIDS.

BIDS isn't infallible. I have compared it against my list of checkerspot
papers extracted from other journal references. It missed quite a few.

> <snip>
> >
> >> 2) Some species of insect are killed just by the action of the toxin
> >> (i.e. Bombyx mori, Plodia interpunctella). Many others are killed by a
> >> combination of the toxin action and septicaemia from the bacterium.
> > 
> >I suppose you could describe anthrax in humans as septicaemia.
> >
> Is this comment relevant to anything?

Bacillus anthracis is closely related to B. thurigiensis. It isn't just a 
matter of accidental septicaemia. It  obviously how the organism breeds. 

> >> 3) If it isn't a toxin, then why are plants expressing the gene
> >> protected from insect pests?
> >> 
> >> Sounds like a toxin to me...
> >
> >Its toxic effects are only a side effect of its true purpose. 
> >Describing it as a toxin  misleads people. Arsenic is toxic but
> >its does not exist to kill people. This molecule that BT produces
> >has a specific design to open holes in the stomach wall of its prey.
> >This allows the Bacillus thurigiensis bacterium to breed.
> >
> Well, this is getting into semantics here so the discussion is getting
> a bit pointless, but by your argument snake venom is not venom it is
> just something that the snake produces to help it feed. Calling it a
> toxin does not mislead people because it is a toxin. If it isn't a
> toxin how does it kill insects? I think you must be using a very
> specialist definition of toxin here.

No what I am saying is that people are being mislead by the term
"Soil bacterium" into thinking it is just an accident that there
is an insecticide in something found in soil.
To give you an example of what I mean, many plants contain alkaloids with
effects that make them useful drugs. It is not an accident since these poisons
will deter herbivores that will associate eating bitter substances with getting
ill. Hypericums contain hypericin which COINCIDENTALLY is an anti-depressant
in humans. Having an anti-depressant does not benefit the plant.
The substance is obviously there for a reason but it is not there because
it alters animals brain chemistry.( incidentally it might well give them
a healthy appetite!) BT does not have this specialised protein by coincidence.

It is important that the public are not mislead on this issue 

> <snip>
> >Is its close relative Bacillus anthracis (which causes anthrax) also most
> >truthfully described as a soil bacterium ? Of course not. It is a disease
> >organism just like Bacillus thurigiensis. The fact is that since the
> >protein is being put in food, it does not sound good to say that it comes from
> >a bug that eats its victims from the guts outwards. 
> >
> >
> If most Bt lives in the soil, if most of its reproduction is carried
> out in the soil, then it's a soil organism. It is also an
> entomopathogen, but that doesn't stop it being a soil organism. You
> implied that calling it a soil organism was a deliberate attempt to
> mislead the public by the GM plant developers, but in fact they were
> just calling it what it is.

The role in which its genes are being used is as a substitute for using the
whole organism for its pathogenic qualities. It is misleading not
to call it by the ecological role in which it is being used. 
There is as I have said very little
research on non-pest species. The fact that we are still discovering 
new strains of BT shows that we don't know what it always does.

> >> I would be interested to know your source for this information: maybe
> >> someone in the organic food industry is not being truthful.
> >
> >Charles Darwin and logic :-). Seriously though this is a predatory
> >organism. If not why does it have a highly sophisticated, intricate,
> >specialised tool to get into its victims?
> It is sometimes a pathogen. It is sometimes a saprophyte, and the
> latter more often than the former. One thing it is not, by the way, is
> a predator (see any ecology textbook for a definition of predator). I
> wasn't going to mention this but since you seem so concerned about the
> correct use of certain words..... :-)

OK you're right I should be more precise ( it is easier to
use terms like predator for some people here than entomopathogen)
 but it is still an insect killer. 
The way I  see it is either this range of organisms has these intricately
formed proteins that are specially constructed so that after multiple 
sets of digestion they miraculously fit, like different complicated keys into
different complicated locks, by accident or because evolution designed them 
that way.

If it is an accident then why hasn't selection removed the burden of 
producing these genes? The only other possibilty I can see is that
there is something wrong with the theory of evolution and
as you're posting from a BRITISH academic site I am sure you're not
saying that. (Some Americans don't believe in modern biology.)

In any case I am growing tired of debating this point and I am sure
that this must be the case for others on the list. If only for the
wear and tear on certain people's salivary glands :-)

We will just have to agree to differ on this.
> Cheers
> Rob

Neil Jones- Neil at
"At some point I had to stand up and be counted. Who speaks for the
butterflies?" Andrew Lees - The quotation on his memorial at Crymlyn Bog
National Nature Reserve

More information about the Leps-l mailing list