> This  [an LD-50 of 192 ppb] is way high.  

I'm sorry, but 192 ppb is the consensus number.
I'll quote from the FAQ Bayer put out in May 2007:

"Over 10 studies of acute contact and acute oral toxicity to honey bees
following EPPO test guideline No. 170 have been performed with imidacloprid.
The reported oral LD50 values range from 0.0037 to greater than 0.070
µg/bee,  with all but one study reporting a value greater than 0.005 µg/bee.
The reported contact LD50 values are less variable, and range from 0.042 to
0.104 µg/bee."

> I am sure you have a reference for 192, but "consensus"?

Yes, I call the general agreement of ten studies a "consensus". 

> Bayer's own researchers have placed it [LD50]
> as low as 20 ppb at one time (Kirschner)

This is simply incorrect. Someone may have made a typo in something you
read.

> I just posted a reference to a paper on chronic 
> toxicity by... Suchail  which gives specific 
> LD50's for certain lengths of time. 

Funny thing about Suchail... no one could reproduce his results.  I'll quote
again from the FAQ:

"Suchail et al. (2001) conducted acute and chronic oral toxicity studies
with imidacloprid and 6 metabolites in honey bees and reported unexpectedly
high chronic toxicity.  

Significant mortality was seen for each of the 7 chemicals.... There was
little difference in chronic toxicity between dose levels or between
compounds.  

...very surprising given that 4 of the compounds tested were non-toxic to
honey bees in the acute test.  

The temporal pattern of mortalities observed was largely independent of the
compound or dose being tested, suggesting an extraneous factor and not the
test compounds might have been responsible for the mortality observed in
this study.  Schmuck (2004) had four independent laboratories repeat Suchail
et al’s chronic test with imidacloprid.  Three contract labs in Germany and
one in the UK again exposed honey bees via the diet for 10 days to spiked
sucrose solution containing 0.1, 1 and 10 ppb.  In all four labs, no
compound-related mortalities were observed at any of these test
concentrations."


[R. Schmuck, "Effects of a Chronic Dietary Exposure of the Honeybee Apis
mellifera (Hymenoptera: Apidae) to Imidacloprid
Environ. Contam. Toxicol. 47, 471–478 (2004)]


So Suchail's work was clearly flawed, and was not reproduceable.  This sort
of thing happens sometimes, and it shows up best in citation indexes. Flawed
work is rarely cited, while quality work is cited often.  But access to
citation indexes costs serious money or requires an indutrial grade library
card from a university.

> at that concentration [50 - 100 pbb] bees are doing what Bayer calls
"trembling dances"

These biochem guys are rarely enthusiastic beekeepers, so it is not
surprising that they might think a tremble dance was unusual.
Here's a decent description of what a tremble dance actually is, and why
bees do a tremble dance:
http://en.wikipedia.org/wiki/Tremble_dance


> I posted an abstract of a paper... (Suchail) 

One needs to read the ENTIRE PAPER.  Then one need to read other papers
published afterwards to get the picture.

If you can't find them, e-mail me, and I'll send you copies of what I have.
To start, here is a pdf of the Suchail paper, and the Schmuck paper that
debunked Suchail's very unexpected
findings:

http://bee-quick.com/reprints/imd/Suchail_2001.pdf
http://bee-quick.com/reprints/imd/Schmuck_2004.pdf

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