Black queen cell virus is named for its most visible effect: queen cells whose walls darken and in which the pupa dies.

Why it matters in queen rearing

This is the virus that can ruin a rearing round without an obvious cause.

• The pupa dies in the cell
• The cell wall discolours dark brown to black
• The contents become watery and break down
• Fewer queens emerge than expected

In worker brood the virus generally causes no visible damage; it is in queen cells that it becomes apparent.

The connection with nosema

This virus is often found together with nosema, and the two reinforce one another. A colony with a high nosema burden more often shows loss of queen cells.

Where rearing rounds fail repeatedly, investigating nosema is more useful than looking for the virus itself.

What triggers it

• Nosema
• A cell builder that is too weak or exhausted
• Pollen shortage
• Stress from repeated opening and moving
• Varroa and the weakened immunity that comes with it

What to do

There is no treatment for the virus. The approach targets conditions:

• Use strong, well-fed cell builders
• Rotate cell builders; do not let one feed series after series
• Ensure abundant pollen
• Renew comb — nosema spores persist in it
• Keep Varroa under control
• Limit disturbance around the cells

What to remember

Queen cells failing without an obvious cause is a reason to look at the condition of the cell builder — not at the rearing technique.