> I do not know why a hive would die in summer unless it went queenless and was not requeened. 

In large scale operations, this is likely to be quite common. If the hives swarm and need to requeen themselves, the queen needs to get mated and return to the correct hive. Which will be difficult if there are hundreds of hives all painted the same color and places in rows or on pallets. 

Queenlessness is also responsible for losses in winter. So, technically these hives are not "dying" but dwindling down to nothing. But the surveys refer to "losses" -- not hives dying, per se. 

Starvation is probably the most common cause of actual death of entire colonies, and leaves obvious evidence (no honey, pile of dead bees). Outright pesticide kills used to be seen frequently, but are rare any more.

PLB

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