Bt corn flap

[Jim Taylor]

Hey, wish you guys would stop calling this a "corn flap." I stay perpetually
hungry, and it sounds like something you should put syrup on and eat. How
about another, less titillating term?

Jim Taylor
----- Original Message -----
From: "Chris J. Durden" <drdn at mail.utexas.edu>
To: <leps-l at lists.yale.edu>
Sent: Wednesday, March 29, 2000 12:41 PM
Subject: Re: Bt corn flap


> At 07:52  29/03/00 GMT, you wrote:
> >On Wed, 29 Mar 00 14:14:10 GMT, Neil at nwjones.demon.co.uk (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.
> >
> >>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.
> - - - -- - -
>   I have been seeing one form of either *B. thuringensis* or polyhedrosis
> viris with some frequency since 1954. It occurs on butterfly larvae that
> feed on nettles *Urtica* spp. It wipes out a population in about 3 days,
> leaving the larvae as black limp sacks hanging from the claws of a proleg.
> I see it most often in remote wilderness areas. Species that I have seen
> affected are *Vanessa atalanta*, *Nymphalis milberti* and *Polygonia
> satyrus*. It seems to be a very real fact of life/death for these species
> and may prevent them from eradicating the hostplants, which are not common
> in boreal regions.
> - - - - -(Chris)
> >
> > It exists is a variety of strains which
> >>differ from each other. These natural predators are one of the factors
which
> >>influence the population dynamics of many species. For example Bacillus
> >>species are a major natural cause of mortality in the endangered
Jamaican
> >>Swallowtail Papilio homerus.
> >>
> >
> >Intersting. Do you have a reference for the P. homerus stuff? I'd like
> >to know more. Most of the reports I'm aware of of Bt causing much
> >mortality in wild populations comes from stored product pests, which
> >live in environments that are particularly good for Bt spores and
> >toxin to survive in (dry, no UV), and it doesn't seem to be important
> >in the population dynamics of many species in natural environments.
> >
> >>Engineered corn contains PART of a gene from ONE strain of Bacillus
> >>thurigiensis. This is an important factor to take into consideration.
> >>
> >>The variability of wild Bacillus thurigiensis is an important tool in
its
> >>armoury. The "toxin" (actually a tool for enabling it to gain access to
> >>the insect's body) exists in nature in such a range of forms that it is
> >>difficult for insects to develop immunity.
> >
> >You seem to have some resistance with calling it a 'toxin'. Consider
> >the following
> >
> >1) When an insect ingests Bt toxin, the toxin binds to the gut wall if
> >the insect is of a species susceptible to that strain of Bt. It
> >creates large pores in the cell membranes, disrupting their water
> >balance and causing them to rupture. The gut lining of an insect
> >that's ingested Bt toxin looks like someone's fired a shotgun at it if
> >you look at it with an SEM.
> >
> >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.
> >
> >3) If it isn't a toxin, then why are plants expressing the gene
> >protected from insect pests?
> >
> >Sounds like a toxin to me...
> >
> >>However the ecological consequences of flooding an ecosystem with high
> >>levels of one specific form of the toxin are difficult to predict.
> >
> >Well not really. What will happen is:
> >
> >>...  resistance will rapidly spread in the
> >>populations of many species. It is also likely that this will facilitate
> >>the developement of resistance to other wild strains. This could easily
> >>occur once the majority of the population of a species carries a gene
> >>that that works against one strain. Natural selection works just
> >>like this.
> >>The consequences are that we actually decrease the ability of Natural
> >>predators to control pests. That is not a smart thing to do.
> >
> >Quite right. Unfortunately as far as I'm aware the organic industry
> >doesn't seem to be doing a great deal to manage the resistance that
> >may develop from their use of 'high levels of one specific form of the
> >toxin', which many of them are doing, I'm afraid.
> >
> >>
> >>What also worries me is that the industry has chosen repeatedly to
> >>describe Bacillus thurigiensis as a "soil bacterium" this is
> >>not truthful at all. I tend to distrust people who are not truthful.
> >>
> >
> >Well Neil, the thing is that Bt IS a soil bacterium. If you want to
> >find Bt, look in the soil. Most isolates of Bt come from the soil.
> >It's a damn sight easier to find it in the soil than it is in diseased
> >insects, for example.
> - - - - -
> Is it growing in the soil, or merely biding its time? A lot of biota that
> cannot be described as soil biota, occurs there when waiting for
> opportunities elsewhere.
> - - - - -(Chris)
>  It is also found elsewhere, I'll grant you that,
> >but if you want to describe Bt and you only have two words, 'soil
> >bacterium' is pretty good.
> >
> >I would be interested to know your source for this information: maybe
> >someone in the organic food industry is not being truthful. Remember,
> >it is an industry, and whereas some organic growers are dedicated
> >selfless protectors of the environment there are others who are in it
> >for the money, and they stand to lose big wads of cash if the public
> >decides that one of their most effective control agents is no longer
> >acceptable.
> - - - -
> Wow. You could say that about the GM/GE nebbishes too!
> - - - -(Chris)
> >
> >Best wishes
> >
> >Rob Knell
> >
> >
>