I posted on this report earlier this year, yet it is worth noting that it is another clear example of researchers looking into multiple causes for colony collapse, including imidacloprid.

Here the researchers claim to be the first to detect imidacloprid in Greek bees, yet this still point to the combination of Nosema and virus as the most likely cause of the colony collapse. 

We present: the infection of Greek honey bees by multiple viruses; the presence of N. ceranae in
Greek honey bees and the first record of imidacloprid (neonicotonoid) residues in Greek honey bee 
tissues. The presence of multiple pathogens and pesticides made it difficult to associate a single specific
cause to the depopulation phenomena observed in Greece, although we believe that viruses and N. 
ceranae synergistically played the most important role.

Sudden deaths and colony population decline in Greek honey bee colonies
Journal of Invertebrate Pathology
J Invertebr Pathol. 2010 Sep 23. [Epub ahead of print]

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