Nosema and Chalkbrood

There are many diseases that can threaten honey bees, including American and European Foulbrood. The frequency and severity of these diseases vary considerably, as do the ease with which they are resolved. Here we look at two more potential threats to honeybees, namely Nosema and Chalkbrood.



Nosema is one of, if not the most, common diseases among adult honey bees. It is a parasitic, spore-forming fungus.

There are two forms of Nosema.

Nosema Apis is the original Nosema and has been recognized in the US for over 100 years. It attacks the cells lining the gut of the adult honey bee and is associated with colder climates. This is because bees are more prone to Nosema Apis when they have limited opportunities to fly.

Nosema Apis causes dysentery and bees confined to the hive, for example, due to poor weather, will defecate in the hive. The spores from Nosema Apis are then spread rapidly by bees moving around the hive. The spore is highly resistant to extreme temperatures and dehydration and cannot be eradicated by freezing contaminated comb.

Nosema Ceranae is thought to have been in the US for a couple of decades but was only reported as such in 2007. It is more of a year-round threat. For reasons that are not entirely clear, it tends to affect foragers considerably, who may die away from the hive. This results in an imbalance in the normal ratios of nurse to forager bees.


Bees in a hive infected by Nosema Apis may live half their expected lifespan, and the colony as a whole produces less honey. Visible signs can include:

  • Excreta on comb
  • An inability for some bees to fly
  • The inability to build up the colony in the spring
  • Piles of dead bees

However, these signs are not always evident, particularly for a hive that isn’t widely infected. The only surefire way to tell is through microscopy. This means you either have the skills necessary to identify Nosema or you send it off to a lab for analysis.

One fortunate aspect of Nosema is that because infected workers usually do not attend to the queen, she is less likely to be infected.


It’s the same old story – strong, healthy colonies are much better positioned to avoid significant outbreaks of Nosema than weak colonies. This means large, healthy colonies are desired, especially going into the winter. Since Nosema Apis is associated with “hive-bound” bees, placing the hive in a sunny location that encourages and eases the bees’ ability to fly is a major factor.

Good nutrition is important in preventing Nosema
Much of this will be dependent on the honey flow. Protein from pollen is essential.

This isn’t as simple as assuming that a strong honey flow will provide all the bees need. Some flowers offer less protein than others, with poor examples including sunflowers, corn, and dandelion. If these represent the primary source of pollen, then bees may still not get the protein variety they need.

Some beekeepers respond to a weak honey flow or one that doesn’t have the nutritional variety needed by feeding a pollen supplement.


An antimicrobial agent called Fumagillin can be used to treat hives infected with Nosema. While it doesn’t actually kill the Nosema spores, it does prevent them from reproducing in the gut of the adult honey bee.

Cleanup of Nosema is a significant and convoluted task. Options include fumigation with certain chemicals or scorching equipment with a blowtorch.



Chalkbrood is not a severe disease and rarely kills an entire colony. However, it can have serious consequences for the overall strength of the colony, which in turn limits their ability to resist other diseases. Honey production may also fall significantly.

Chalkbrood is caused by the fungus Ascosphaera apis. Like Nosema Apis, it affects the gut but does so only with larvae.  It is most common as temperatures change rapidly. For example, in spring the brood nest can grow rapidly but there may not be enough workers to keep it warm. This can cause conditions supportive of Chalkbrood. As summer arrives and temperatures rise, Chalkbrood often declines.

Transmitting of spores is a major concern
Spores can easily be transmitted from colony to colony by robbers and also via beekeeping equipment.


When Chalkbrood strikes, larvae die and become mummified and hard. The result is larvae that look like chalk, hence the name. Over time the dead larvae may become darker, which can potentially confuse the new beekeeper.

The dead larvae are often found at the entrance to the hive. Their hard texture and white color are the reason that many beekeepers call them “mummies”.


Moisture in the hive is a major contributor to Chalkbrood, so taking steps to reduce that will help. Another helpful measure is to provide a food supplement when natural food resources are at a premium. Also, to potentially clean out Chalkboard spores, replacing darkened, aged brood comb may help.

The beekeeper can inadvertently increase the chances of Chalkbrood. Exposing brood to lower temperatures for too long can cause “chilled brood”, which increases the likelihood of Chalkbrood. New beekeepers have a tendency to search just a little too long for that elusive queen during their inspections, allowing comb and brood to cool.

Similarly, stress on bees caused by too many inspections – another common rookie mistake – increases the chances of Chalkbrood (or, in fact, many other potential problems).


Infections can often clear up on their own, over time. Some beekeepers may choose to requeen when a significant outbreak of Chalkbrood occurs since some strains of honey bees are more resistant than others. Some consider Thymol-based products to be helpful in clearing up Chalkbrood.