"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.
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