Israeli acute paralysis virus belongs to a group of closely related viruses that also includes acute bee paralysis virus and Kashmir bee virus.

The group

These three are genetically close and indistinguishable in the field. They share the same characteristics:

• They occur at low levels without symptoms
• They are introduced directly into the haemolymph by Varroa
• Once activated they progress rapidly and lethally

For the beekeeper the distinction between the three has no practical bearing; the measure is the same.

The attention it received

This virus came to prominence during investigation of sudden colony losses. It was found more often in affected colonies than in healthy ones.

A settled causal role has not been established, however; the picture points rather to an interplay of factors in which Varroa and virus load converge.

Symptoms

• Rapid loss of adult bees
• Trembling, uncoordinated bees
• Dark, hairless bees rejected by guards
• A colony collapsing in a short time

Confirmation requires laboratory testing.

What makes it dangerous

The speed. Unlike deformed wing virus, which exhausts a colony gradually, this group can lead to collapse in a short time.

By then there is no time left to act — which means the measure must be taken in advance.

Control

No product acts on the virus. The only genuinely effective measure is keeping Varroa under control, with a measurement before winter bees are reared.

Alongside that: varied pollen, no colonies of unknown origin, and selection for hygienic behaviour.