The larvae die from aflatoxins (toxins) produced by the fungus in the capped cell before they begin to pupate. Spores germinate in the larvae’s guts and the mycelium rapidly grows through the entire larvae’s bodies. Once the mycelium reaches the surface, it begins to produce fruiting bodies. Even adult bees can ingest fungal spores with their food and the mycelium will develop in a similar way to that in the larvae.
Broods: hard larvae bodies, the body surfaces of the affected larvae appear yellow-green when infested with Aspergillus flavus, and grey-green when infested by Aspergillus fumigatus. The mummies are attached tightly to the cell wall, and the larvae cannot be removed by the worker bees as the mycelium also grows through the cell walls to some extent. Instead, the cell walls are covered in propolis or are gnawed down by the bees.
Adult bees: the fungus grows out of the abdominal segments and produces spores. Hard abdomens, crawling bees in front of the hive. Infections in adult bees often remain undetected, as they die outside the hive.
The spores can cause inflammation in the nose, eyes, throats and lungs of humans.
The spores are transmitted between colonies via landing at the wrong hive, robbery, changing combs or feeding with contaminated honey. Air circulation, spores attached to bees and food are the main causes of the spores spreading within a colony.
Infections are mainly caused by contaminated food, and quite seldomly by fungal spores via the larvae’s Skin.
There is no medication to treat stonebrood licensed for the Austrian market. Infected colonies must be culled and the combs burnt if stonebrood has been diagnosed and the hives must be cleansed using a 3% sodium carbonate solution or via flame sterilised.
A protective mask should be worn for all work with infected bees. Hands should be washed thoroughly and work clothes washed separately. Creating artificial swarms is not considered a good idea, given the severe spore contamination in the bees and the risks to the beekeeper.