This came over the transom.  It is a MUST READ:
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Thought you might be interested in this nice summary of imidacloprid. You
can view it at www.pesticide.org/imidacloprid.pdf

The scientist who prepared it is Caroline Cox and ... she got
the soil persistence data from the US Environmental Protection Agency
registration information that was submitted by Bayer. It is interesting
that the authorities know that imidacloprid can persist for over a year is
that it is highly mobile in soil but did not give it a Restricted Use
Classification. Sounds like economic reasons are more important than
decisions based on science.

allen

http://www.internode.net/HoneyBee/Imidacloprid/