Christina,
  I have been searching for the irreversible mechanism of imidacloprid.  I haven't found any compelling paper so far that shows or suggest that imidacloprid is irreversible, however either the chloro pyridine or the nitro guanidine may for covalent adducts to the target receptor so I am not disagreeing there, however we can agree that it does not randomly alkylate proteins in living organisms, since it wouldn't be able to reach it's target.  
  So it like every other molecule animals eat is subject to ADME (Absorbtion, distribution, metabolism, and excretion), it is not like lead which is an accumulative toxin which sequesters itself in bones and even lead will eventually dissipate from your body.  It is only in the event that imidacloprid actually reaches sufficient concentration in the target areas for it to maintain residency in the receptor to then form a covalent irreversible adduct (if in fact it does) and is no longer subject to metablolism and excretion.  Also, I assume that insects also have protein turn-over and that inactivated receptors may be degraded and re-expressed.  
  It seems to me that you are extrapolating some of the aspects of reversible inhibition to make conclusions based on this paper that aren't really supported.  Is there an actual study that shows periodic exposure to very small amounts on neonicotinoids results in cummulative effects?  Mark

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