"Moosh:]" wrote:
On 29 Jul 2003 08:52:24 GMT, Brian Sandle
posted:
As we discussed with DDT, anything used for too long breeds resistant
creatures.

So? The point is that the use of BT in the plant and on the plant is
hardly different. When the insects are not present, they can't be
developing resistance.

Where is there a place without insects?
Welcome to the real world, where things are not black and white,
where we don't have either 0 or trillions of insects but varying
degrees inbetween, where not all insects are dumb enough to
keep eating bt until they've got a fatal dose but different ones
eat different amounts and so trigger varying amounts of
selective pressure.

When the pesticide is interrupted then resistance to it is no
longer an advantage.

And the pest destroys your crop, and you go bankrupt.

Not necessarily, if the natural predators have not been wiped
out by overuse of pesticides and the plants natural defenses
have not been weakened by toxic and/or cultural damage to
the soil ecology.

Then DDT will work again, or Bt. But if it is there all
the time resistance to it remains an advantage for pests.

Sorry, "there all the time" means nothing if the pests are not there.
It might as well be withdrawn if the pests are absent.
No contact, no advantage for the resistant mutations.

When home gardners use it, or non-GM soy farmers &c, it is only present as
needed, then disappears.

And why does it matter if it's there or not, if the pests aren't
predating the crop?

There are always a few about, from the mandatory refuges, or other crops
near by.

But how does this matter? The chances of a resistance mutation are so
much lower.

Check out what's already happened:
Independent on Sunday (London) March 30, 2003
INSECTS THRIVE ON GM 'PEST-KILLING' CROPS
BY GEOFFREY LEAN ENVIRONMENT EDITOR

Genetically modified crops specially engineered to kill pests in fact
nourish them, startling new research has revealed.

Biotech companies have added genes from a naturally occurring poison,
Bacillus thuringiensis (Bt), which is widely used as a pesticide by
organic farmers.
Drawbacks have already emerged, with pests becoming resistant to the
toxin. Environmentalists say that resistance develops all the faster
because the insects are constantly exposed to it in the plants, rather
than being subject to occasional spraying.

But the new research - by scientists at Imperial College London and the
Universidad Simon Rodrigues in Caracas, Venezuela - adds an alarming new
twist, suggesting that pests can actually use the poison as a food and
that the crops, rather than automatically controlling them, can actually
help them to thrive.

They fed resistant larvae of the diamondback moth - an increasingly
troublesome pest in the southern US and in the tropics - on normal
cabbage leaves and ones that had been treated with a Bt toxin. The larvae
eating the treated leaves grew much faster and bigger - with a 56 per
cent higher growth rate.

They found that the larvae "are able to digest and utilise" the toxin and
may be using it as a "supplementary food", adding that the presence of the
poison "could have modified the nutritional balance in plants" for them.

And they conclude: "Bt transgenic crops could therefore have
unanticipated nutritionally favourable effects, increasing the fitness of
resistant populations."

The original scientific study is published at
Ecology Letters Volume 6 Issue 3 Page 167 - March 2003
Could Bt transgenic crops have nutritionally favourable effects on
resistant insects?
Ali H. Sayyed, Hugo Cerda and Denis J. Wright

Which product? When resistance develops to one insecticide, another
must be used.

Or somebody wakes up, thinks outside the box, and gets out
of the pesticide trap.
--
delete N0SPAAM to reply by email

On Thu, 07 Aug 2003 07:20:22 -0700, Walter Epp
posted:

"Moosh:]" wrote:
On 29 Jul 2003 08:52:24 GMT, Brian Sandle
posted:
As we discussed with DDT, anything used for too long breeds resistant
creatures.

So? The point is that the use of BT in the plant and on the plant is
hardly different. When the insects are not present, they can't be
developing resistance.

Where is there a place without insects?

The relevant insects are those that damage the crop. If they don't,
they won't be ingesting BT.

Welcome to the real world, where things are not black and white,
where we don't have either 0 or trillions of insects but varying
degrees inbetween, where not all insects are dumb enough to
keep eating bt until they've got a fatal dose but different ones
eat different amounts and so trigger varying amounts of
selective pressure.

And this happens with applied BT, only better coz the BT slowly
reduces due to washing off and so on. So if you want to be accurate,
applied BT can be worse than expressed BT wrt resistance development.

When the pesticide is interrupted then resistance to it is no
longer an advantage.

And the pest destroys your crop, and you go bankrupt.

Not necessarily, if the natural predators have not been wiped
out by overuse of pesticides and the plants natural defenses
have not been weakened by toxic and/or cultural damage to
the soil ecology.

BT is very specific, so your fear of pest predator damage is
unfounded. Why are you postulating that the natural defences of the
plant will be weakened? What are you trying to say about the soil
ecology?

Then DDT will work again, or Bt. But if it is there all
the time resistance to it remains an advantage for pests.

Sorry, "there all the time" means nothing if the pests are not there.
It might as well be withdrawn if the pests are absent.
No contact, no advantage for the resistant mutations.

When home gardners use it, or non-GM soy farmers &c, it is only present as
needed, then disappears.

And why does it matter if it's there or not, if the pests aren't
predating the crop?

There are always a few about, from the mandatory refuges, or other crops
near by.

But how does this matter? The chances of a resistance mutation are so
much lower.

Check out what's already happened:
Independent on Sunday (London) March 30, 2003
INSECTS THRIVE ON GM 'PEST-KILLING' CROPS
BY GEOFFREY LEAN ENVIRONMENT EDITOR

Genetically modified crops specially engineered to kill pests in fact
nourish them, startling new research has revealed.

Biotech companies have added genes from a naturally occurring poison,
Bacillus thuringiensis (Bt), which is widely used as a pesticide by
organic farmers.
Drawbacks have already emerged, with pests becoming resistant to the
toxin. Environmentalists say that resistance develops all the faster
because the insects are constantly exposed to it in the plants, rather
than being subject to occasional spraying.

Occasional spraying will result in many occasions where dose is
sublethal. Ideal circumstances for resistance development.

But the new research - by scientists at Imperial College London and the
Universidad Simon Rodrigues in Caracas, Venezuela - adds an alarming new
twist, suggesting that pests can actually use the poison as a food and
that the crops, rather than automatically controlling them, can actually
help them to thrive.

BT is a protein, and can be used as a food by non-sensitive insects,
but then no more than any other protein.
Nothing magic about it.

They fed resistant larvae of the diamondback moth - an increasingly
troublesome pest in the southern US and in the tropics - on normal
cabbage leaves and ones that had been treated with a Bt toxin. The larvae
eating the treated leaves grew much faster and bigger - with a 56 per
cent higher growth rate.

Can you quote any of this study? It costs to read it, I believe.

They found that the larvae "are able to digest and utilise" the toxin and
may be using it as a "supplementary food", adding that the presence of the
poison "could have modified the nutritional balance in plants" for them.

Along with all the other thousands of proteins the plant supplies
them?

And they conclude: "Bt transgenic crops could therefore have
unanticipated nutritionally favourable effects, increasing the fitness of
resistant populations."
The original scientific study is published at
Ecology Letters Volume 6 Issue 3 Page 167 - March 2003
Could Bt transgenic crops have nutritionally favourable effects on
resistant insects?
Ali H. Sayyed, Hugo Cerda and Denis J. Wright

Which product? When resistance develops to one insecticide, another
must be used.

Or somebody wakes up, thinks outside the box, and gets out
of the pesticide trap.

We can't survive without pesticides. Afterall, plants have never been
able to for many millions of years.

Moosh:} writes
They fed resistant larvae of the diamondback moth - an increasingly
troublesome pest in the southern US and in the tropics - on normal
cabbage leaves and ones that had been treated with a Bt toxin. The larvae
eating the treated leaves grew much faster and bigger - with a 56 per
cent higher growth rate.

Can you quote any of this study? It costs to read it, I believe.

They found that the larvae "are able to digest and utilise" the toxin and
may be using it as a "supplementary food", adding that the presence of the
poison "could have modified the nutritional balance in plants" for them.

Along with all the other thousands of proteins the plant supplies

The devil is in the detail, I suspect.

I would be astonished if the amount of BT was enough to constitute a
supplementary feed. However I can see an easy mechanism to produce this
result, although whether this is true of this trial or not I cannot say.

Plants attacked by pests will elevate their toxin levels as a response.
If the untreated plants were under attack (or their neighbours were)
then they would increase their toxin level.

If the Bt plants perceived themselves in a pest-free environment then
toxin levels would be low, if the untreated perceived themselves is a
pest zone then they would elevate their toxin levels.

The toxin levels in plants are known to have strong effects on growth
rates of animals eating them.

--
Oz
This post is worth absolutely nothing and is probably fallacious.
Note: soon (maybe already) only posts via despammed.com will be accepted.

On Fri, 8 Aug 2003 06:18:46 +0100, Oz
posted:

Moosh:} writes
They fed resistant larvae of the diamondback moth - an increasingly
troublesome pest in the southern US and in the tropics - on normal
cabbage leaves and ones that had been treated with a Bt toxin. The larvae
eating the treated leaves grew much faster and bigger - with a 56 per
cent higher growth rate.

Can you quote any of this study? It costs to read it, I believe.

They found that the larvae "are able to digest and utilise" the toxin and
may be using it as a "supplementary food", adding that the presence of the
poison "could have modified the nutritional balance in plants" for them.

Along with all the other thousands of proteins the plant supplies

The devil is in the detail, I suspect.

I would be astonished if the amount of BT was enough to constitute a
supplementary feed. However I can see an easy mechanism to produce this
result, although whether this is true of this trial or not I cannot say.

Plants attacked by pests will elevate their toxin levels as a response.
If the untreated plants were under attack (or their neighbours were)
then they would increase their toxin level.

If the Bt plants perceived themselves in a pest-free environment then
toxin levels would be low, if the untreated perceived themselves is a
pest zone then they would elevate their toxin levels.

The toxin levels in plants are known to have strong effects on growth
rates of animals eating them.

Interesting thoughts, thanks.
I'm not rich enough to afford $19US for the dubious value of reading
the full article. If someone else has it, then please post here.

It amazed me that such a tiny amount of one protein could produce such
growth differences. Your explanation of growth inhibition from a
predated crop certainly fits.

On Fri, 08 Aug 2003 04:20:48 GMT, "Moosh:}"
wrote:

On Thu, 07 Aug 2003 07:20:22 -0700, Walter Epp
posted:
[Quoting Independent on Sunday (London) March 30, 2003:]
.. Environmentalists say that resistance develops all the faster
because the insects are constantly exposed to it in the plants, rather
than being subject to occasional spraying.

Occasional spraying will result in many occasions where dose is
sublethal. Ideal circumstances for resistance development.

However, reminding ourselves of the perils of assumption-based
reasoning, let us hear what the experienced farmers over at
sci.agriculture has to say about that.

..

On Fri, 08 Aug 2003 05:48:09 GMT, "Moosh:}"
wrote:
On Fri, 8 Aug 2003 06:18:46 +0100, Oz
posted:

Someone wrote:
They fed resistant larvae of the diamondback moth - an increasingly
troublesome pest in the southern US and in the tropics - on normal
cabbage leaves and ones that had been treated with a Bt toxin. The larvae
eating the treated leaves grew much faster and bigger - with a 56 per
cent higher growth rate.
..
Plants attacked by pests will elevate their toxin levels as a response.
If the untreated plants were under attack (or their neighbours were)
then they would increase their toxin level.
..
It amazed me that such a tiny amount of one protein could produce such
growth differences. Your explanation of growth inhibition from a
predated crop certainly fits.

It doesn't fit or explain anything at all, since the same cabbage leaf
material was fed in all treatment groups in the experiment. The
researchers grew a single cabbage crop, cut discs from its leaves, and
fed the discs to different groups of larvae kept in petri dishes, with
or without Bt toxin fortification.

Torsten Brinch writes
It doesn't fit or explain anything at all, since the same cabbage leaf
material was fed in all treatment groups in the experiment. The
researchers grew a single cabbage crop, cut discs from its leaves, and
fed the discs to different groups of larvae kept in petri dishes, with
or without Bt toxin fortification.

What % DM was leaf and what BT in the two trials?
What was the protein level in the DM of the two feeds?

Were both groups fed ad-lib?

I if the former was under 1% or so and the latter true then I would want
to see independent verification.

--
Oz
This post is worth absolutely nothing and is probably fallacious.
Note: soon (maybe already) only posts via despammed.com will be accepted.

Torsten Brinch writes
On Fri, 08 Aug 2003 04:20:48 GMT, "Moosh:}"
wrote:

On Thu, 07 Aug 2003 07:20:22 -0700, Walter Epp
posted:
[Quoting Independent on Sunday (London) March 30, 2003:]
.. Environmentalists say that resistance develops all the faster
because the insects are constantly exposed to it in the plants, rather
than being subject to occasional spraying.

Occasional spraying will result in many occasions where dose is
sublethal. Ideal circumstances for resistance development.

However, reminding ourselves of the perils of assumption-based
reasoning, let us hear what the experienced farmers over at
sci.agriculture has to say about that.

There are two arguments:

1) Apply full dose and kill 99.999% except the 0.001% that have a
resistance gene and next season you will have a 100% resistant
population. If (as is common) you have a pest with a very high
reproductive rate then you are stuffed in a year or two.

This is what happened for dimfop resistant blackgrass.
This might be typical of single gene resistance (not tolerance).

This will happen whether or not the gene is less efficient than the
'natural' gene.

2) Apply a reduced rate, kill 99% of the pest, leave 1% of which 1:1000
have a resistance gene. Hope the resistance gives less efficient pest,
outbred by 'natural' genes, leaving a final pest population still with
about 0.001% resistance. So no change.

Most field weeds are more tolerant of pesticides than their wild
relatives, but often not by much.

Pesticides acting on single genes are MUCH more likely to become
completely useless due to single point mutation.

Pesticides with multiple-point action are pretty unlikely to develop
resistance.

Obviously simultaneously using several pesticides with different action
mimics multiple-point resistance.

If a pesticide targets a key site, that is hard for the pest to alter
because it is critical (perhaps used in many subsystems or is very
basic), then tolerance rather than resistance seems to be the normal
mode of action (eg hormone weedkillers, IPU). I haven't seen it stated,
but I suspect the progeny are less competitive.

Certainly resistant blackgrass seems to be highly susceptible to mildew,
for example.

--
Oz
This post is worth absolutely nothing and is probably fallacious.
Note: soon (maybe already) only posts via despammed.com will be accepted.

"Walter Epp" wrote in message
...
"Moosh:]" wrote:
On 29 Jul 2003 08:52:24 GMT, Brian Sandle
posted:
As we discussed with DDT, anything used for too long breeds resistant
creatures.

So? The point is that the use of BT in the plant and on the plant is
hardly different. When the insects are not present, they can't be
developing resistance.

Where is there a place without insects?
Welcome to the real world, where things are not black and white,
where we don't have either 0 or trillions of insects but varying
degrees inbetween, where not all insects are dumb enough to
keep eating bt until they've got a fatal dose but different ones
eat different amounts and so trigger varying amounts of
selective pressure.

We have eliminated some insects. The new world screw worm fly has been
killed back to the Panama canal and it use to range in to Kansas in the
fall. It appears that with BT cotton, cultural practices, spraying scents
that disrupt their breeding and releasing sterile males will do the job.
http://www.soybeandigest.com/ar/soyb...pink_bollworm/ Once that is done
that insect no longer needs any control measures unless that is a population
in Mexico that we have to keep pushed back. And Mexico has been very
cooperative on working with us on pest control.

Unfortunately that won't work on common boll worms because they will eat
about any thing there is.


Gordon

"Torsten Brinch" wrote in message
...
On Fri, 08 Aug 2003 04:20:48 GMT, "Moosh:}"
wrote:

On Thu, 07 Aug 2003 07:20:22 -0700, Walter Epp
posted:
[Quoting Independent on Sunday (London) March 30, 2003:]
.. Environmentalists say that resistance develops all the faster
because the insects are constantly exposed to it in the plants, rather
than being subject to occasional spraying.

Occasional spraying will result in many occasions where dose is
sublethal. Ideal circumstances for resistance development.

However, reminding ourselves of the perils of assumption-based
reasoning, let us hear what the experienced farmers over at
sci.agriculture has to say about that.

The idea of planting a refuge of non BT crop so the worms can feed on non BT
crops and inter breed with the millers raised on the BT crop was carefully
though out and seems to be working. There is some question if third world
farmers will abide by the refuge requirements but in most cases the small
field size and mixture of crops will provide alternate crops for the boll
worm to feed on and should produce enough millers that are not exposed to BT
to keep resistance down. Also they plan to change BT proteins periodically
to further reduce the likelihood of resistance. BollGard II is available
this year in Australia and I believe Bollguard I will not be available next
year. There are lots of BT proteins to choose from.

In http://ag.arizona.edu/pubs/general/r...nkbollworm.pdf 1 in 10
pink boll worms were found to be resistant to BT cotton in1997 the second
year BT cotton was grown. The resistant to the BT protein did not increase
in 98 or 99 with half the area in BT cotton. The lack of resistance to BT
developing was a surprise to the researchers who expected an increase in
resistance. So the refuge method seems to be sound.

More on the theory of refuges.
http://www.nature.com/nsu/990805/990805-5.html

Monsanto has traps world wide for boll worms and monitors the crops and
weeds around them by satellite imagery and on the ground inspection looking
for signs of resistance. It is one of their biggest nightmares and they are
doing every thing they can to spot it early and combat it should it arise.

We have been doing everything we can to extend the life of pesticides for
the last 20 years and hopefully we have learned something in that time.

Gordon

"Moosh:}" wrote:
On Thu, 07 Aug 2003 07:20:22 -0700, Walter Epp
posted:

"Moosh:]" wrote:
On 29 Jul 2003 08:52:24 GMT, Brian Sandle
posted:
As we discussed with DDT, anything used for too long breeds resistant
creatures.

So? The point is that the use of BT in the plant and on the plant is
hardly different. When the insects are not present, they can't be
developing resistance.

Where is there a place without insects?

The relevant insects are those that damage the crop. If they don't,
they won't be ingesting BT.

but they can pass resistance genes to those who didn't
ingest but can fly in and have a resistant feast.

Welcome to the real world, where things are not black and white,
where we don't have either 0 or trillions of insects but varying
degrees inbetween, where not all insects are dumb enough to
keep eating bt until they've got a fatal dose but different ones
eat different amounts and so trigger varying amounts of
selective pressure.

And this happens with applied BT, only better coz the BT slowly
reduces due to washing off and so on. So if you want to be accurate,
applied BT can be worse than expressed BT wrt resistance development.

Applied Bt is the most accurate way to minimize selective pressure.
The crude approach of continual and high exposure makes for high
selection pressure for resistance.

When the pesticide is interrupted then resistance to it is no
longer an advantage.

And the pest destroys your crop, and you go bankrupt.

Not necessarily, if the natural predators have not been wiped
out by overuse of pesticides and the plants natural defenses
have not been weakened by toxic and/or cultural damage to
the soil ecology.

BT is very specific, so your fear of pest predator damage is
unfounded. Why are you postulating that the natural defences of the
plant will be weakened? What are you trying to say about the soil
ecology?

Mycorrhizal fungi can effectively connect their plant hosts with as
much as 1,000 times more soil area than the roots themselves.
A single gram of soil may contain several miles of fungal hyphae. As they
pump water and mineral nutrients to the roots, the fungi form a
protective armor against disease bacteria around the roots, and sometimes
innoculate the soil with antibiotics that kill disease bacteria.
Root zone fungi and bacteria exude glues (polysaccharides) that bind soil
particles together, resulting in better retention and movement of air and
water. Mycorrhizal fungi break down nitrogen into forms that can be used
by plants. Mats of fungi in the soil store nutrients that otherwise would
be likely to dissolve and leach away.

Roundup/Glyphosate is toxic to many beneficial mycorrhizal fungi,
inhibiting growth at levels as low as 1ppm, and increases susceptibility
of crop plants to a number of diseases.

The mycorrhizal hyphal network is easily disrupted by mechanical
disturbance. Disking a field, for example, can greatly reduce the ability
of the soil to make new plants mycorrhizal, even though no fungal material
is actually removed by disking.

Then DDT will work again, or Bt. But if it is there all
the time resistance to it remains an advantage for pests.

Sorry, "there all the time" means nothing if the pests are not there.
It might as well be withdrawn if the pests are absent.
No contact, no advantage for the resistant mutations.

When home gardners use it, or non-GM soy farmers &c, it is only present as
needed, then disappears.

And why does it matter if it's there or not, if the pests aren't
predating the crop?

There are always a few about, from the mandatory refuges, or other crops
near by.

But how does this matter? The chances of a resistance mutation are so
much lower.

Check out what's already happened:
Independent on Sunday (London) March 30, 2003
INSECTS THRIVE ON GM 'PEST-KILLING' CROPS
BY GEOFFREY LEAN ENVIRONMENT EDITOR

Genetically modified crops specially engineered to kill pests in fact
nourish them, startling new research has revealed.

Biotech companies have added genes from a naturally occurring poison,
Bacillus thuringiensis (Bt), which is widely used as a pesticide by
organic farmers.
Drawbacks have already emerged, with pests becoming resistant to the
toxin. Environmentalists say that resistance develops all the faster
because the insects are constantly exposed to it in the plants, rather
than being subject to occasional spraying.

Occasional spraying will result in many occasions where dose is
sublethal. Ideal circumstances for resistance development.

If the spraying is only occasional the selection pressure is low.
If the exposure is continual and high the selection pressure for
resistance is high.
--
delete N0SPAAM to reply by email

"Moosh:}" wrote:
On Thu, 07 Aug 2003 07:20:22 -0700, Walter Epp
posted:

"Moosh:]" wrote:
On 29 Jul 2003 08:52:24 GMT, Brian Sandle
posted:
As we discussed with DDT, anything used for too long breeds resistant
creatures.

So? The point is that the use of BT in the plant and on the plant is
hardly different. When the insects are not present, they can't be
developing resistance.

Where is there a place without insects?

The relevant insects are those that damage the crop. If they don't,
they won't be ingesting BT.

but they can pass resistance genes to those who didn't
ingest but can fly in and have a resistant feast.

Welcome to the real world, where things are not black and white,
where we don't have either 0 or trillions of insects but varying
degrees inbetween, where not all insects are dumb enough to
keep eating bt until they've got a fatal dose but different ones
eat different amounts and so trigger varying amounts of
selective pressure.

And this happens with applied BT, only better coz the BT slowly
reduces due to washing off and so on. So if you want to be accurate,
applied BT can be worse than expressed BT wrt resistance development.

Applied Bt is the most accurate way to minimize selective pressure.
The crude approach of continual and high exposure makes for high
selection pressure for resistance.

When the pesticide is interrupted then resistance to it is no
longer an advantage.

And the pest destroys your crop, and you go bankrupt.

Not necessarily, if the natural predators have not been wiped
out by overuse of pesticides and the plants natural defenses
have not been weakened by toxic and/or cultural damage to
the soil ecology.

BT is very specific, so your fear of pest predator damage is
unfounded. Why are you postulating that the natural defences of the
plant will be weakened? What are you trying to say about the soil
ecology?

Mycorrhizal fungi can effectively connect their plant hosts with as
much as 1,000 times more soil area than the roots themselves.
A single gram of soil may contain several miles of fungal hyphae. As they
pump water and mineral nutrients to the roots, the fungi form a
protective armor against disease bacteria around the roots, and sometimes
innoculate the soil with antibiotics that kill disease bacteria.
Root zone fungi and bacteria exude glues (polysaccharides) that bind soil
particles together, resulting in better retention and movement of air and
water. Mycorrhizal fungi break down nitrogen into forms that can be used
by plants. Mats of fungi in the soil store nutrients that otherwise would
be likely to dissolve and leach away.

Roundup/Glyphosate is toxic to many beneficial mycorrhizal fungi,
inhibiting growth at levels as low as 1ppm, and increases susceptibility
of crop plants to a number of diseases.

The mycorrhizal hyphal network is easily disrupted by mechanical
disturbance. Disking a field, for example, can greatly reduce the ability
of the soil to make new plants mycorrhizal, even though no fungal material
is actually removed by disking.

Then DDT will work again, or Bt. But if it is there all
the time resistance to it remains an advantage for pests.

Sorry, "there all the time" means nothing if the pests are not there.
It might as well be withdrawn if the pests are absent.
No contact, no advantage for the resistant mutations.

When home gardners use it, or non-GM soy farmers &c, it is only present as
needed, then disappears.

And why does it matter if it's there or not, if the pests aren't
predating the crop?

There are always a few about, from the mandatory refuges, or other crops
near by.

But how does this matter? The chances of a resistance mutation are so
much lower.

Check out what's already happened:
Independent on Sunday (London) March 30, 2003
INSECTS THRIVE ON GM 'PEST-KILLING' CROPS
BY GEOFFREY LEAN ENVIRONMENT EDITOR

Genetically modified crops specially engineered to kill pests in fact
nourish them, startling new research has revealed.

Biotech companies have added genes from a naturally occurring poison,
Bacillus thuringiensis (Bt), which is widely used as a pesticide by
organic farmers.
Drawbacks have already emerged, with pests becoming resistant to the
toxin. Environmentalists say that resistance develops all the faster
because the insects are constantly exposed to it in the plants, rather
than being subject to occasional spraying.

Occasional spraying will result in many occasions where dose is
sublethal. Ideal circumstances for resistance development.

If the spraying is only occasional the selection pressure is low.
If the exposure is continual and high the selection pressure for
resistance is high.
--
delete N0SPAAM to reply by email

On Fri, 08 Aug 2003 17:30:23 +0200, Torsten Brinch
posted:

On Fri, 08 Aug 2003 04:20:48 GMT, "Moosh:}"
wrote:

On Thu, 07 Aug 2003 07:20:22 -0700, Walter Epp
posted:
[Quoting Independent on Sunday (London) March 30, 2003:]
.. Environmentalists say that resistance develops all the faster
because the insects are constantly exposed to it in the plants, rather
than being subject to occasional spraying.

Occasional spraying will result in many occasions where dose is
sublethal. Ideal circumstances for resistance development.

However, reminding ourselves of the perils of assumption-based
reasoning, let us hear what the experienced farmers over at
sci.agriculture has to say about that.

Of course, but it is a well known mechanism of resistance development,
sub-lethal doses that leave the partially susceptible mutants still
alive. Antibiotic treatments are a case in point. The importance of
finishing the full course prescribed, and not stopping when you feel
better.

On Fri, 08 Aug 2003 17:30:28 +0200, Torsten Brinch
posted:

On Fri, 08 Aug 2003 05:48:09 GMT, "Moosh:}"
wrote:
On Fri, 8 Aug 2003 06:18:46 +0100, Oz
posted:

Someone wrote:
They fed resistant larvae of the diamondback moth - an increasingly
troublesome pest in the southern US and in the tropics - on normal
cabbage leaves and ones that had been treated with a Bt toxin. The larvae
eating the treated leaves grew much faster and bigger - with a 56 per
cent higher growth rate.
..
Plants attacked by pests will elevate their toxin levels as a response.
If the untreated plants were under attack (or their neighbours were)
then they would increase their toxin level.
..
It amazed me that such a tiny amount of one protein could produce such
growth differences. Your explanation of growth inhibition from a
predated crop certainly fits.

It doesn't fit or explain anything at all, since the same cabbage leaf
material was fed in all treatment groups in the experiment. The
researchers grew a single cabbage crop, cut discs from its leaves, and
fed the discs to different groups of larvae kept in petri dishes, with
or without Bt toxin fortification.

You obviously have the advantage of reading the full paper. Care to
share? So how do you explain the marked growth increase from this tiny
amount of one protein? Has the experiment been replicated? If not,
perhaps we should wait until the attempt has been made?

On Fri, 8 Aug 2003 17:15:49 +0100, Oz
posted:

Torsten Brinch writes
On Fri, 08 Aug 2003 04:20:48 GMT, "Moosh:}"
wrote:

On Thu, 07 Aug 2003 07:20:22 -0700, Walter Epp
posted:
[Quoting Independent on Sunday (London) March 30, 2003:]
.. Environmentalists say that resistance develops all the faster
because the insects are constantly exposed to it in the plants, rather
than being subject to occasional spraying.

Occasional spraying will result in many occasions where dose is
sublethal. Ideal circumstances for resistance development.

However, reminding ourselves of the perils of assumption-based
reasoning, let us hear what the experienced farmers over at
sci.agriculture has to say about that.

There are two arguments:

1) Apply full dose and kill 99.999% except the 0.001% that have a
resistance gene and next season you will have a 100% resistant
population. If (as is common) you have a pest with a very high
reproductive rate then you are stuffed in a year or two.

This is what happened for dimfop resistant blackgrass.
This might be typical of single gene resistance (not tolerance).

This will happen whether or not the gene is less efficient than the
'natural' gene.

2) Apply a reduced rate, kill 99% of the pest, leave 1% of which 1:1000
have a resistance gene. Hope the resistance gives less efficient pest,
outbred by 'natural' genes, leaving a final pest population still with
about 0.001% resistance. So no change.

Most field weeds are more tolerant of pesticides than their wild
relatives, but often not by much.

Pesticides acting on single genes are MUCH more likely to become
completely useless due to single point mutation.

Pesticides with multiple-point action are pretty unlikely to develop
resistance.

Obviously simultaneously using several pesticides with different action
mimics multiple-point resistance.

If a pesticide targets a key site, that is hard for the pest to alter
because it is critical (perhaps used in many subsystems or is very
basic), then tolerance rather than resistance seems to be the normal
mode of action (eg hormone weedkillers, IPU). I haven't seen it stated,
but I suspect the progeny are less competitive.

Certainly resistant blackgrass seems to be highly susceptible to mildew,
for example.

Bottom line though is that BT expressed is no more likely fo cause
resistance development problems than intemittent application of BT.