What are the typical "Causes of loss in commercial apiaries"?

The greatest losses occurred from September through the following March. 
Of the colonies that died over the years, less than 10% appeared to die off
suddenly: i.e. the colonies appeared to be healthy on one colony inspection but were dead
by the following inspection six weeks later. From 9-31% of the colonies died by
dwindling (or failure to thrive); i.e., the population of bees in a colony was observed to
decrease over time until the colony died out. Only one incident of disease causing death
was observed, in which the colony exhibited high levels of chalkbrood disease on the
previous sample date. All other colony deaths were preceded by a problem with the queen.

Queen problems were a common issue across sites, despite the beekeeper
replacing the queens in all colonies annually. Queenless colonies and drone layers were
common (14-100% across sites and years) immediately before colony death
... causes of queen failure are an active area of current honey bee research.

The beekeeper maintained an effective management strategy to control the most
damaging parasite, V. destructor, as well as Nosema spp. and bacterial agents.

Smart, M. S. (2015). The influence of mid-continent agricultural land use on the health and survival of commercially managed honey bee (Apis mellifera L.) colonies (Doctoral dissertation, UNIVERSITY OF MINNESOTA).

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