Stonebrood is a rare, short-lived fungal disease affecting adult honey bees and their larvae. The fungi Aspergillus flavus and Aspergillus fumigatus infect larvae, causing them to mummify before hatching. Bee larvae quickly change color and harden, like stone.
How is stonebrood spread?
Stonebrood spreads when fungal spores from the soil become airborne. They attach to foraging honey bees, comb, and beekeeping equipment. The disease will spread between hives as the result of beekeeping activities as well as robbing, swarming, and drifting.
Recommended reading: What is sacbrood?
How to detect stonebrood
In its early stages, stonebrood is challenging to identify in the hive. However, the fungus grows quickly, resulting in telltale signs of advanced disease.
Beekeepers may identify stonebrood from hive symptoms, but lab tests are required to positively identify the fungus. To detect stonebrood, look for any of the following:
- The infected larva has a whitish-yellow ring close to the head end.
- Dead larvae are extremely hard to crush.
- Black, grey-green, or yellow-green powdery spores on the larvae.
Source: United States Department of Agriculture, Agricultural Research, Service Agriculture Handbook, Number 690
Behavioral signs of stonebrood infestation include bees crawling on the ground outside the hive. They may have swollen abdomens., be unable to fly or appear paralyzed, weak, or agitated.
How to prevent stonebrood
Stonebrood is a fungus from the ground, so preventing these microbes from reaching your bee yard is never a certainty. Beekeepers can help by maintaining healthy hives and using clean equipment and tools.
Positioning hives away from damp areas, keeping them waterproof, and maintaining regular inspections help the colony fight off this disease.
How to treat stonebrood
Treatment approaches vary, and beekeepers should check local regulations to determine if total colony destruction and reporting are required. Below are some recommendations from several reputable sources:
- A document produced by the University of Ljubljana, Slovenia, advise urgent destruction of affected colonies. You can download the free .pdf here.
- A beekeeping guide produced by the Rural Industries Research and Development Corporation in Australia advises, “For practical purposes, the disease may generally be disregarded if good beekeeping methods are practiced.” Download pdf guide here.
- Researchers in Egypt discovered that clove oil and ascorbic acid effectively controlled infested colonies. Source.
From the above, you can see that beekeeping approaches vary depending on what you read. We recommend contacting your local beekeeping association or appropriate government department to get specific advice for your location.
Keep in mind that the disease is compulsorily notifiable in some countries.
7 fast facts about stonebrood
- The fungus is pathogenic to plants, bees, mammals, birds, and other insects.
- Take care around the disease, as the spores can cause respiratory conditions, and the aflatoxins may be carcinogenic.
- Beekeepers with immunocompromised systems should take extreme care around these spores.
- Fungal spores infect adult bees and their larvae.
- The disease has been reported in North America, Europe, Australia, and South America.
- Infected larvae usually die after being capped in their cells before pupation.
- Like chalkbrood, mummies may be spotted at the hive entrance or on the bottom board.
Title: Standard methods for fungal brood disease research.
Authors: Jensen AB, Aronstein K, Flores JM, Vojvodic S, Palacio MA, Spivak M.
Ready to learn more? Check out our guide to honey bee threats here. It reveals some of the most common threats that bees face.