These Are The Warning Signs You Have an American Foulbrood Infection

Published on August 14, 2020

Inspecting a bar of comb for American foulbrood infections

Inspections are key for identifying American Foulbrood infections. Fortunately, our keepers didn't find any cause for concern.

While colony collapse disorder (CCD) is all over the news, American Foulbrood infections are still a major concern for beekeepers, though their prevalence has decreased significantly in the last 100 years. If you’ve been beekeeping for a long time and have multiple colonies, there’s a good chance you’ve encountered this foul-odored infection. Regardless of your experience, it’s an important honey bee disease to be knowledgeable about. It could save the honey bee colonies near your home.

What Is American Foulbrood?

American Foulbrood is a bacterial infection caused by a spore-forming bacterium called Paenibacillus larvae. The spores are what make it difficult to eradicate, as they can live for decades within a hive, continuing to reinfect its inhabitants.

When this bacterium infects a colony, the nurse bees, unbeknownst to them, feed the spores to the larvae before capping the cells. Inside the larva, it infiltrates the midgut, killing the bee baby soon thereafter. When house bees clean out the cell, they spread spores throughout the rest of the hive. So, while it doesn’t kill adult bees, it can absolutely decimate the brood, making it impossible for the colony to proliferate its own existence.

Remember, healthy brood reflects a healthy colony.

How Does It Spread?

In order to minimize the spread of this nasty bee disease, you have to understand how it spreads. For instance, within the colony, the workers spread the spores throughout the hive, and this includes honeycomb.

Then, when robber bees come to the hive to steal a sweet treat, they bring delicious carbohydrates and bacterial spores with them back to their own hive.

Additionally, you can spread an American Foulbrood infection from colony to colony (if you have multiple) by failing to properly sterilize equipment between hives.

Finally, if your colony swarms, it can bring American Foulbrood spores with it, risking nearby bee populations.

How Do You Recognize American Foulbrood?

Inspections are key for identifying American Foulbrood infections. Fortunately, our keepers didn’t find any cause for concern.

Your job as a beekeeper is to know what to look for during inspections in order to identify an American Foulbrood infection. Here are the signs you’ve got a messy brood infection on your hands, and you should take action:

Brood cells will begin to transform from convex to concave, and they will turn brown and greasy.
The brood pattern will be patchy and scattered, though this could indicate other infections as well, and is not exclusive to American Foulbrood.
Cells may have perforations.
The pupal mass underneath the cappings appears brown and mucousy.

Numbers five and six are typically seen in later stages of infection, when it may be too late.

Dark, hard scales appear in the bottom of uncapped cells; these are difficult to remove.
There will be a distinct, sulfur-like odor coming from the hive.

What Do You Do Next?

If you want to confirm you have an American Foulbrood infection on your hands, there are a couple of simple tests you can do. Here’s the first one:

The Ropiness Test

Identify a cell with the characteristic brown, sunken, and greasy appearance.
Using a toothpick, the end of a matchstick, or a twig, insert the object into the cell.
Stir the contents around before slowly removing the object from the cell.
If you have an American foulbrood infection, the pupal mass should come out of the cell, attached to the object, forming a mucous-like string up to 2 cm long.

Furthermore, there are other tests you can perform, including using a blacklight to visualize scales (they glow!) and using a milk mixture. You can find instructions for these tests and more here.

Can You Treat American Foulbrood?

Unfortunately, American Foulbrood has no cure. Your best bet is to prevent and manage the infection with integrative pest management, which focuses on using non-chemical methods to prevent and manage the infection. This includes:

Arranging your colonies in a horseshoe shape or snake-like shape
Sterilizing equipment between colonies
Only purchasing new equipment, not used, for your beekeeping
Cull your combs on a three-year cycle
Wash your hands thoroughly between colonies

If you are certain you have an infection on your hands, the best course of action is to burn the infected hive and its contents.

Final Thoughts

Just like humans, honey bees can spread diseases to each other – from colony to colony. If you identify an American Foulbrood infection in your colony, it’s imperative that you take appropriate action to prevent the spread of disease amongst your local honey bee populations. By being aware and acting quickly, you can help preserve generations of honey bees to come.

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Caitlin Knudsen

Caitlin Knudsen is a content writer for Beepods with a passion for lifelong learning and psychology. She is an avid gardener, grower of houseplants, and does recipe development and food photography in her spare time.