Interesting speculation on what 'might' have killed the bees down under, but none of them address the sentence thate:

   "The honey on some of the hives was ready to be harvested, 
   but is now contaminated. The company estimated the loss 
   was tens of thousands of dollars."

Presumably there was physical evidence that caused the beekeepers to determine their crop was contaminated. If so, that would rule out varroa, nosema ceranae, and deaths from sprayed fields.  

Let's hope that the press chooses to report on:  

  "The NSW Department of Primary Industries has taken samples 
  of dead bees and poisoned honey from the hives to be analysed 
  at its forensic laboratory operated by the Environmental 
  Protection Agency in Lidcombe."

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