Stonebrood is a brood disease caused by fungi of the genus Aspergillus. It resembles chalkbrood but is rarer, and it has one aspect the other brood diseases do not.

The picture

• The dead larva hardens and mummifies
• The mummies take on a greenish-yellow or grey-green colour
• They are harder and darker than in chalkbrood
• As sporulation proceeds a dusty appearance develops

Distinguishing it from chalkbrood

• Colour: Chalkbrood is white and later greyish-black; stonebrood greenish
• Hardness: Stonebrood mummies are distinctly harder
• Frequency: Stonebrood is far less common
• Adult bees: Stonebrood can also affect adults

Conditions

• Damp and poor ventilation
• A weak colony
• Mouldy comb and mouldy stores
• A damp site

As with chalkbrood, the disease is often not the real problem but an indication about conditions in the hive.

The human health aspect

This is what sets stonebrood apart from other bee diseases. The fungi involved are species that can cause respiratory problems in people with weakened immunity.

It is therefore sensible to wear a mask when handling heavily affected comb. Shaking out mouldy comb so that dust rises is not advisable.

What to do

• Remove affected comb and take it out of circulation
• Improve ventilation; reduce moisture in the hive
• Restrict the space to what the colony can keep warm
• Review the site. Avoid permanently damp, shaded positions
• Strengthen the colony
• Requeen if it recurs persistently

There is no specific treatment, and generally none is needed; the disease recedes when conditions improve.