Filamentous bee virus differs from the other bee viruses in being considerably larger and carrying a different type of genetic material.

The characteristic

In heavy infection the haemolymph of the bee turns milky white instead of clear.

That is one of the few virus findings assessable by eye. It is not distinctive, however: haemolymph also turns cloudy in septicaemia.

What it affects

The virus multiplies in tissues of adult bees, including the fat body — the same tissue Varroa feeds on and on which winter hardiness depends.

Distribution and significance

It is found widely, often alongside nosema. The two are regularly found in the same colonies.

Its independent significance is unclear, however. It is equally found in apparently healthy colonies, which means presence is not the same as harm.

Diagnosis

Milky haemolymph is an indication, not a diagnosis. Confirmation requires laboratory testing, and the distinction from septicaemia cannot be made in the field.

Control

No product acts on this or any other bee virus. The measures are indirect:

• Keep Varroa under control
• Address nosema by renewing comb and limiting damp
• Varied pollen for immunity
• Limit stress

What to remember

A colony with cloudy haemolymph and crawling bees is a colony under stress. The question is not which virus, but why this colony is weakened — and the answer almost always lies with Varroa, damp or nutrition.