Several things:

1. Here is a summary for your consideration: 
http://www.beekeeping.com/articles/us/imidacloprid_bayer.htm
If it is correct, then at least volatility is not a concern, so the air should be fairly safe 
after the droplets clear.  As for the nearby water the bees may gather in the period 
after spraying, that is less certain, but should cause negligible exposure at worst. I 
could be wrong.

2. Can you predict the time of day and weather conditions at time of application?
That is going to have a huge effect on potential exposure and your best course of 
action.

In seed canola, the one time they had to spray with bees present, we were 
consulted on the insecticide used (and chose something considered fairly safe as I recall) 
and the time of day.  We left hives open and specified spraying at dusk after bee flight.  
As I recall, damage was minimal.  The fact that I cannot remember indicates that it 
was not a huge concern.

The timing was, though.  As I recall, we were working in one yard well before dusk and 
a spray plane came directly toward us, then turned away when he saw us (we 
assumed).  Was he planning to spray early and changed his mind when he saw 
witnesses?  Crop dusters can only fly a short time after bees quit for the day, so that 
window is short and some may wish to fudge the timing a bit.

2. We moved bees in the late fall and winter after they settled and on cool days when 
they were not flying and never saw any adverse effects.  Sometimes we trucked 
individual hives around for days when we were evening out yards and pallets. We 
looked for harm and saw none at all.

3. US beekeepers move bees in winter across frozen states on open flatbeds and I 
have not heard of nosema resulting from that cause alone.

4. I don't know how you plan to close entrances, but if the hives are not flying much,
grouping the pallets and tarping with light-proof tarps for up to 24 hours may be a good 
way.  You need several forklifts and a crew to do it on short order, but if the season is 
over, the days are cool, and the bees are not flying you can group them in daytime 
and any bees that come out will just follow the hive and go back in.  Location memory 
will be weak and drifting won't happen if they have not been foraging for a few days.  
You'll know if there will be a problem as soon as you have moved a few, assuming you s
top and watch to make sure.

Of course hot weather would make the above a bad idea.  Otherwise a little ventilation 
around the tarp edges should suffice.  When we we hauled hies around in fall as 
mentioned, we simply shaded them from direct light with a tarp. Quiet, settled hives 
on't use much air.

---
Caveat.  I assume Juanse and his crew are expert enough to know the parameters 
at a glance.  Others should consider their own level of expertise before assuming 
they could make the suggestion work for them.

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