What Is Stonebrood? A Beekeeper’s Reference Guide

A beekeeper inspecting a hive for diseases like stonebrood.

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

  1. The fungus is pathogenic to plants, bees, mammals, birds, and other insects.
  2. Take care around the disease, as the spores can cause respiratory conditions, and the aflatoxins may be carcinogenic.
  3. Beekeepers with immunocompromised systems should take extreme care around these spores.
  4. Fungal spores infect adult bees and their larvae.
  5. The disease has been reported in North America, Europe, Australia, and South America.
  6. Infected larvae usually die after being capped in their cells before pupation.
  7. Like chalkbrood, mummies may be spotted at the hive entrance or on the bottom board.

Interesting research

Title: Standard methods for fungal brood disease research.
Authors: Jensen AB, Aronstein K, Flores JM, Vojvodic S, Palacio MA, Spivak M.

Read the research>

Stonebrood is a rare disease that affects honey bees, caused by a group of fungi called Aspergillus. This fungus can harm bees in different life stages, from larvae to adults. Some strains of this fungus produce toxic chemicals called aflatoxins, which can be harmful and might be the main reason bees die from this disease.

A deeper understanding of stonebrood and chalkbrood diseases requires an integrated approach that combines genetics, ecology, microbiology, and behavioral studies. For instance, determining the genetic markers that make honey bees susceptible or resistant to these fungal infections can provide insights into the breeding of resistant honey bee strains.

The honey bee colony is a complex ecosystem, home to numerous pathogens, symbionts, and parasites. Understanding how stonebrood and chalkbrood diseases interact with other pathogens, such as viruses, bacteria, and parasites, will provide comprehensive knowledge about the health dynamics of honey bee colonies.

While stonebrood is rare, its potential impact on honey production, pollination, and overall colony health cannot be underestimated.

Research to determine these diseases’ economic impact can drive better policymaking and funding for further studies.

Addressing these gaps ensures the health and productivity of honey bee colonies and has broader implications for agriculture, ecosystems, and global food security.

Ready to learn more? Check out our guide to honey bee threats here. It reveals some of the most common threats that bees face.

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