There's a new paper -- Influence of Pollen Nutrition on Honey Bee Health: Do Pollen Quality and Diversity Matter?
Available as a open download -- http://www.plosone.org/article/fetchObject.action?uri=info%3Adoi%2F10.1371%2Fjournal.pone.0072016&representation=PDF
Most interesting and crucially important in my reading are the detailed survivorship curves after Nosema ceranae infection:
This shows that bees infected with the new Asian virulent Nosema ceranae are going die in enormous numbers at the time of House Bee >> Forager Bee transition. The key marker for CCD is loss or foragers (depopulation with brood and queen still resident). Nosema ceranae is isolated as the single controlled "insult" is shown to effect this depopulation in this study.
This of course was identified as a disease factor many years ago, and Fumagilin treatment has become routine. However, a really important paper was published in March '13 --Nosema ceranae Escapes Fumagillin Control in Honey Bees
Free access at: http://www.plospathogens.org/article/info%3Adoi%2F10.1371%2Fjournal.ppat.1003185
This paper shows that Nosema ceranae actually becomes more virulent
by treatment. The old Nosema -- N. apis -- is wiped out (as are many competitive organism) -- and N. Ceranae expands into the void created by the vacuum.
Huang W-F, Solter LF, Yau PM, Imai BS (2013) Nosema ceranae Escapes Fumagillin Control in Honey Bees. PLoS Pathog 9(3): e1003185. doi:10.1371/journal.ppat.1003185