I forgot to address one last question:

Randy says:

“Again, if the binding were truly irreversible, wouldn't we expect to see every forager on seed-treated canola to drop dead after a day or so?”

No.  As you and many others have pointed out, the bees are getting “sub-lethal” doses, unless they bring home dust.  There are lots of AChR receptors in each synapse...thousands of them in fact.  If just a small number are blocked, the rest can continue to work.  These “blocked” receptors represent current leaks.  The neuron’s function is compromised, but not eliminated.

Sub-lethal means impaired.  This could explain behavior problems.  It also means delayed mortality.  This could explain shortened lifespans.

To the neuron, being chronically depolarized by leaky membranes is life-threatening.  The cell must try to recover, or it dies.  One way to cope could be to reduce the number of ion channels in the membrane.  Another way to cope would be to REPLACE the blocked AChR channels. The neuron could also increase the number of sodium-potassium pumps in the membrane...these are used to restore the resting membrane potential, but they cost a lot of metabolic energy so adding more of them will wear out the cell.   Finally, the neuron could also up-regulate (increase numbers) of AChR receptors, thus getting more functional ones on-line, while reducing the disruptive depolarizing current (caused by the blocked AChR receptors) by decreasing the numbers of ion channels.  Upregulation of AChR receptors may happen in insects.  We know it happens in people…this is part of nicotine dependency physiology.

One of my earlier questions on Bee-L was:  Could bees adapt to neonics like people adapt to nicotine?

Christina

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