European Foulbrood

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European Foulbrood is a disease that can damage your honey bee colonies. It is caused by a bacterium Melissococcus plutonius. This disease only affects the brood or young developing bees in the hive. However, the loss of the next generation can have devastating effects on colony strength.  Here are a few tips that you need to know about dealing with European Foulbrood in your hives.

Beekeeper inspecting frame from hive that may have European Foulbrood.

Foulbrood Diseases

The developing young bees in the hive are called brood. This term “bee brood” represents all stages of larval growth and the pupa (capped brood) too.

And, we usually throw the bee eggs in there too. So, a brood disease is something that affects the non-adult members of the colony.

While any number of pathogens could cause harm to young, there are two major brood diseases that worry beekeepers. American Foulbrood and European Foulbrood are both are caused by bacteria.

Often called (EFB), European Foulbrood is often confused with the more deadly AFB or American Foulbrood

AFB is a serious issue for any apiary. In fact, in some regions it is law that any AFB infected colonies be burned – along with all the equipment.

You can easily see why it is important to try to correctly identify which one may be present in your hives.

Some of the disease symptoms are similar – dead brood that stinks? Honestly, in my experience, all dead brood stinks.

When a colony dies, the beekeeper needs to try to determine the cause. Reusing a box containing AFB spores is one of the biggest dangers of buying used beekeeping equipment.

That type of foulbrood can live in old equipment for up to 50 years.

The fear of having AFB causes some beekeepers to destroy their colony or equipment when there is no reason to do so. Taking the time to asses the situation may save your bees.

How Dangerous is European Foulbrood?

EFB is not necessarily a death sentence in the same way that American Foulbrood can be. Rather it is a stress disease, that only seems to show up in adverse conditions.

A strong colony may control the disease all on their own with no assistance from a beekeeper.  Usually, light infections with a section of European Foulbrood on a frame or two require no treatment. 

If most of the brood in the hive look good, check back in a week to monitor the condition.

However, a severe EFB infection can result in large population loses. This could cause the hive to not be able to continue. 

Too few bees in a colony opens the doors for problems with robbing bees, various pests and the possibility of not storing enough food for Winter.

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Healthy white bee larvae in comb.

Symptoms of European Foulbrood

While adult bees can carry the disease, it is the bee brood that are affected. So, this is where we look for signs of the disease.

Of course, symptoms for other conditions such as varroa infestations, nosema and viruses are often similar to one another.

A beekeeper usually finds EFB by noticing dead larvae in the brood nest of the colony. Healthy bee larvae are white and shiny. Anytime you see, brown, yellow or dark larvae – there is a problem.

With EFB, larvae usually die before the pupal stage. This means they expire before the wax capping is added. 

This is when the larvae are still young and mobile, this mobility allows the dying larva to twist in the cell. They may appear deflated with parts of the trachea system easily visible.

An area of young larva, yellow or brown in color and twisted in the wax cell is the most obvious sign of the disease. 

The dead may have a slight ropiness when the contents of the cell is pulled out – but not to the level of AFB.

How is it Spread

While EFB can occur at any time, it is more common in mid- late Spring. The bacterium that causes EFB overwinters inside the colony. 

It can be found in the cell walls of comb, in feces and even on the wax debris found on your bottom board

You can find a lot of gnarly things down there including wax moth larvae and Small Hive Beetles. A good reason to clean the bottom board periodically.

In every colony, some of the young worker bees are serving as nurses. They consume large amount of protein-rich bee bread

This causes the special brood food glands in their mouth to develop and produce food for the baby bees.

Feeding young is a constant job with thousands of trips being made to each brood cell. Alas, this life-giving food may also contain the bacterium that causes European Foulbrood

Tiny bee larvae are eating machines. The only thing they do is eat and grow. When the bacteria reached the mid-gut it multiplies competing with the young for food.

This causes the larvae to become ravenous and needing more and more food. 

Nurse bees in hive feeding larvae.

Sometimes, the nurse bees recognize when a larva is “not behaving normal”. They may decide that something is wrong and remove the infected from the hive. Otherwise, the young bees starve from lack of nutrition.

In addition to spreading within the hive by nurse bees, it also spreads from hive to hive. Swarms, drifting bees that go from one hive to another (common with drones) and even absconding colonies take the bacteria with them.

European Foulbrood Treatments

If colonies are affected to the point that you need to take action, there are some steps to take that can help the bees.

But first, can you likely rule out American Foulbrood? A state bee inspector may be able to come take a look.

Another help with diagnosis is the field kits for AFB that you can buy. Once you are comfortable you are indeed seeing signs of EFB – these options can help.

  • requeen the colony
  • break the brood cycle
  • chemical treatment – antibiotics

Requeening the colony can help with EFB on two fronts. First, some “strains” of bees have a bit more resistance to the bacterium.

Maybe a new queen will produce daughters that have the hygienic trait of removing infected larvae.

Another way to help is to make a break in the brood cycle. (Of course, introducing a new queen does this too. There will be a delay in new brood while the queen is being released from her cage.)

In a light infection, a break in the cycle gives the nurse bees time to clean out the diseased young. This results in less active bacterium in the hive.

The last option is chemical treatment of antibiotics. In recent years, many beekeepers have moved away from using antibiotics for EFB.

However, “oxytetracycline HCL” sold as Terramycin is labeled for treatment of European Foulbrood in hives.

This powder is mixed with sugar or sugar water and fed to the colonies. At this time, a VFD (Veterinary Feed Directive) is needed to purchase Terramycin. This means you need a veterinarian – for your bees prescription 🙂

Rebuilding the Colony After EFB

All types of honey bee larvae are susceptible. Workers, drones and developing queens may be affected.

No strain of honey bees is immune to European Foulbrood but some do show a bit more resistance.

Keep stock of colony condition as they recover from a setback like this. You want to see lots of new brood growing and fewer diseased ones.

In some apiaries, a honey flow with fresh nectar coming in clears the problem up quickly. When we work to keep our colonies strong and healthy, they are able to take care of more problems on their own. Isn’t this what we all strive for?

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