> treating "after the bloom" doesn't really 
> mean anything unless we assume that there 
> is no residual imidacloprid in the tree 
> from one year to another.

Maples and other deciduous trees tend to drop
blooms and pollen in late spring, and drop their 
leaves in fall, so all that lasts from year to 
year would be the wood and roots.  Any "residual"
pesticide may not be an issue, as it would certainly
remain in the "dead" wood, but the bulk of it would 
be flushed from the vascular system, as the amount 
of water that moves through a tree in a month is 
very impressive.

Prior experiments using dyes such as this one
may be instructive in determining the exact amount
that might exist as a second-season residual:

http://tinyurl.com/3l7xqs
or
http://www.treelink.org/joa/1999/nov/06_evidence_for_the_downward_movement.p
df

The point made by the paper cited is this:

"It appears that portions of trunk-injected 
materials are transported downward into the 
roots and are then transported upward in the 
sapstream in the following season or seasons."

Anyone tried woodpeckers?  

****************************************************
* General Information About BEE-L is available at: *
* http://www.honeybeeworld.com/bee-l/default.htm   *
****************************************************