What Is Chalkbrood? + Free Printable Guide

A beekeeper collecting honey and inspecting the brood for diseases like chalkbrood

Chalkbrood is a honey bee disease caused by the fungus Ascosphaera apis. If untreated, it mummifies developed larvae, disrupting hive activity and reducing honey production.

Although chalkbrood rarely kills the colony, a good understanding of its symptoms, lifecycle, and treatment will benefit beekeepers.

What are the symptoms of chalkbrood?

Chalkbrood symptoms vary depending on the infection’s stage and its severity. Some common symptoms include:

  • Larvae with a white, chalky coating.
  • Black or gray fungal infection at later stages of the disease.
  • Shrunken, mummified larvae in brood cells and other hive parts.
  • A sour, foul-smelling odor coming from the hive.
  • Noticeable declines in adult bee numbers.
  • Decreased honey production and other hive resources.
A top-down image of brood with chalkbrood
Brood showing signs of chalkbrood.

How does chalkbrood spread?

Chalkbrood spores are highly infectious and spread as foraging bees transfer contaminated pollen. Drifting bees, air currents, or beekeeping equipment also distribute sticky fungal spores.

What can beekeepers do to prevent chalkbrood?

Keep hives safe from chalkbrood by taking preventive measures before an outbreak occurs. Recognizing early signs of infection and correct treatment will help the colony. Below are some practical tips for beekeepers to follow:

  • Check hives regularly for signs of disease: Look for mummified larvae or white patches on combs or frames.
  • Increase ventilation in your bee boxes: Increased air circulation reduces humidity inside the hive, limiting the spread of fungal spores.
  • Keep hives clean: Remove debris, like old wax comb and propolis, that may harbor fungal spores.
  • Reduce hive stress: Chalkbrood impacts stressed colonies with low populations, bad weather, inadequate food supplies, varroa mite infestations, and other diseases.
Chalkbrood mummies on the hive floor.
Chalkbrood mummies on the hive floor.

Lifecycle of chalkbrood

The lifecycle of chalkbrood can be divided into several stages:

  1. Fungus is introduced to the hive through spores carried on adult bees’ bodies or contaminated honey and pollen.
  2. Spores germinate and grow in the cells of the hive where bee larvae are developing.
  3. The fungus infects the larvae, causing them to develop into white, chalky-looking mummies.
  4. The infected larvae die, and the mummies remain in the cells of the hive.
  5. The fungus grows and produces spores, which can spread to other larvae and cause new infections.

The cycle continues until the infection is controlled or the hive dies.

Risk period

Factors that trigger chalkbrood include:

  • Overly dry or wet conditions
  • Low and high temperatures
  • A failing queen
  • Poor nutrition
  • Transferring hives
  • Bad hive management

Related reading: The beekeeper’s guide to sacbrood.

Prevention methods

The best way to prevent the spread of chalkbrood is to keep the hive clean and healthy and monitor for any signs of infection.

  1. Regularly clean and disinfect hive tools and equipment to minimize the spread of spores.
  2. Consider replacing old combs every few years, as they can harbor spores.
  3. Ensure good hive ventilation to keep the hive’s inside drier and less conducive to fungal growth.
  4. Elevate the back of the hive slightly to allow any moisture to drain.
  5. Strengthen weak hives by adding frames of brood from strong, disease-free colonies.
  6. Place hives in areas that receive morning sunlight and avoid damp, low-lying areas.

How do you treat chalkbrood?

There are no chemical treatments for chalkbrood. Beekeepers should remove all spore sources, then reduce hive stress factors.

Spotting mummies in the comb is a sign the worker bees aren’t doing their job. Requeening with a more disease-resistant stock will help.

Varroa mites are a common precursor to chalkbrood. If their population is getting too high, a course of Apistan may be required.

Check out our guides on the symptoms of European foulbrood and how to identify American foulbrood.

A starving colony will struggle to maintain a healthy, disease-free hive. Feed the hive sugar syrup or a pollen substitute during a nectar dearth.

Make sure hives are clean and well-ventilated to encourage air circulation. Hive boxes should fit snugly to help with insulation and maintain optimal temperatures within the colony.

Closeup shot of chalkbrood disease.
Closeup shot of chalkbrood disease.

Chalkbrood vs. stonebrood – what’s the difference?

Chalkbrood and stonebrood are two common fungal infections affecting honeybees. Chalkbrood affects larvae in the hive, while stonebrood affects adult bees and their larvae. Both may spread on foraging honey bees, contaminated brood, and on beekeepers’ tools as they move between hives.

What is a bee brood disease?

A bee brood disease is any disease that affects the immature stages of the honey bee, including the eggs, larvae, and pupae. Common examples include American foulbrood, European foulbrood, and chalkbrood.

Bacteria, viruses, fungi, and other parasites can cause these diseases. They can have a devastating effect on bee colonies.

Can I use a split banana to get rid of chalkbrood?

Some beekeepers split a banana and place it on the brood frames to remove chalkbrood. This technique is simple and cheap, but we have never tried it and can’t vouch for its efficacy.

Where is chalkbrood found around the world?

Chalkbrood impacts beehives in most beekeeping nations, including the United States, Canada, and Mexico. It is also found in parts of Europe, including the United Kingdom, France, Germany, and Spain.

In Asia, chalkbrood has spread through China, Japan, and India. The fungus has worked its way through much of Australia.

South America, Africa, and the Middle East also have this disease.

What is chalkbrood similar to?

Stonebrood: caused by the fungus Aspergillus, this disease also results in mummified larvae. However, stonebrood mummies are typically harder and have a stone-like appearance, unlike the chalky appearance seen with chalkbrood.

American Foulbrood (AFB): a bacterial disease caused by Paenibacillus larvae, AFB affects bee brood. While its symptoms and effects differ from chalkbrood, some superficial similarities exist in that infected larvae die and have a changed appearance. AFB, however, is far more deadly and can wipe out entire colonies.

European Foulbrood: another bacterial disease affecting honeybee brood, but less severe than AFB. Infected larvae often appear twisted and discolored.

Interesting research

We’ve included some interesting research about chalkbrood. To save you some time, our team read and summarized the papers.

Authors: M Gilliam, S Taber III, GV Richardson

Published in: Apidologie, 1983

Our summary: Researchers tested honey bee colonies to see how good they were at removing sick or dead baby bees. They labeled these colonies as “resistant” (good at cleaning) or “susceptible” (not so good at cleaning).

Next, they exposed the colonies to chalkbrood, checking for disease symptoms in various parts of the hive.

Due to significant variation, the study found it hard to see clear differences between the resistant and susceptible groups. However, the resistant colonies were generally better at removing the signs of disease.

Findings suggest that bees sense sick baby bees before we see the signs. It’s important to check multiple parts of the hive to understand the full impact of the disease.

The research also found that chalkbrood is more likely to spread in colonies that aren’t good at cleaning. Efficient housekeepers control the infection by removing sick bees, possibly reducing the disease’s chance of survival.

Research link: Click to download pdf.

Authors: Kathryn A. LeCroy, Erin Krichilsky, Heather L. Grab, T’ai H. Roulston, Bryan N. Danforth

Published in: Journal of Applied Ecology

Our summary: Beekeepers sometimes introduce new types of bees, like mason bees, to help with farm pollination. But transferring them can also spread disease.

In this study, the researchers looked for chalkbrood in the homes of local and introduced mason bees. Community scientists took samples from various habitats in the Mid-Atlantic region of the US.

Results showed that:

  • Fungus, usually found in Japan, existed in Virginian hives.
  • Areas with increased introduced bees meant local bees were more likely to have the fungus.
  • Increased farmland meant local bees had a higher chance of getting chalkbrood disease.
  • Bringing bees from other areas for farming introduces diseases that spread to local bee populations.

Research link: https://doi.org/10.1111/1365-2664.14399

Authors: K.A. Aronstein, K.D. Murray

Published in: Journal of Invertebrate Pathology, Volume 103, Supplement, 2010, Pages S20-S29.

Our summary: Chalkbrood is a honey bee disease caused by the Ascosphaera apis fungus that is spreading globally. Its classification has been updated using modern molecular methods.

This research reviews the disease’s spread, how it affects bees, and the biology of the fungus. It also discusses new ways to control the disease, tools for identifying it, and recent studies on its genetics.

Research link: https://doi.org/10.1016/j.jip.2009.06.018.

Final words

Chalkbrood is a disease affecting honey bees worldwide. It is caused by a fungus known as Ascosphaera apis, which infects larvae within a colony.

Beekeepers should keep clean and well-ventilated hives to help prevent outbreaks of this disease.

Selecting bee breeds with excellent hive hygiene, such as pure Russian bees, will also help. They will quickly remove spores and diseased larvae before the chalkbrood overwhelms the colony.

Further reading:

Image attribution: “Courtesy The Animal and Plant Health Agency (APHA), Crown Copyright”. Sourced from BeeBase Gallery.

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