The varroa mite is endemic throughout both feral and cultivated honey-bee colonies.

BBC: Honey-bees found to have bite that stuns

The Israeli acute paralysis virus (and, perhaps, the mystery virus) may have had such a devastating effect there because of the presence of a parasite called the varroa mite.

ECONOMIST: A virus may help explain colony collapse disorder

To investigate, scientists looked at two common pesticides: neonicotinoids, which are used to control pests on oil seed rape and other crops, and a group of organophosphate chemicals called coumaphos, which are used to kill the Varroa mite, a parasite that attacks the honey bee.

BBC: Neonicotinoid pesticides 'damage brains of bees'

The main suspects for causing bee deaths are viruses and other pests acting in tandem, especially the aptly named Varroa destructor mite.

FORBES: Bee-ing Smart: Regulators Must Distinguish Activists' Bad Dreams From Good Evidence

There is also Varroa, a parasitic mite, which has been another problem in bees for some time, and which might also transmit the IAPV.

ECONOMIST: Agriculture: The bees are back in town | The