On Wed, 13 Aug 2003 11:09:54 GMT, Mooshie peas
wrote:

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?

You mean the 56% increase? It is beyond me where the authors get that
particular figure from. On the face of it the data shows a growth rate
increase of only about 30 %, and I would be wary to accept even that.

The main observation in the experiment IMO is that feeding BT
fortified substrate (10ppm) to larvae, re-selected to yield high Bt
resistance (LC50~200 ppm), increased their mean pupae weight
significantly - about 20% - relative to feeding them non-BT fortified
substrate -- while leaving their time to pupation unchanged or perhaps
a bit shorter.

Has the experiment been replicated?

I don't know, Jack. You can ask the authors if they are working on
that or something similar, email: h dot cerda at ic dot ac dot uk

If not, perhaps we should wait until the attempt has been made?

Funny you did not get that thought while you and Oz were happily
explaining the findings. Boy, you couldn't even wait until you'd
read the article :-)