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I remember when I first got into beekeeping. I was overwhelmed with anticipation of getting to watch my bees grow and producing my own honey. In order to restrain myself from opening my hive every day, I decided to open my beekeeping books instead. I learned more about honey bee biology, all the factors that make up a colony, what were the nectar producing plants in my area, plus all the cool beekeeping gadgets you can buy. It didn't take long for me to come across the various pests and diseases that can affect honey bee health.
Once I got past the big scary ones (you know, Varroa mites and American Foulbrood,) I came across perhaps the lesser-known diseases, one of which is Chalkbrood. Chalkbrood is often considered a "secondary" disease, meaning that it most likely won't be the reason a colony dies, but it has the potential to significantly weaken it.
In Texas, we often see Chalkbrood in the spring when the weather is cool and damp, but it is possible for symptoms to appear in other times of the year. So, what exactly is this disease and what can we do about it?
Chalkbrood is a fungal infection (causative agent is Ascosphaera apis) first reported in the United States in 1972. It is a brood disease that will affect larvae that are 3-4 days old. Fungal spores are ingested and germinate in the gut of a larva. Through germination, the fungus quickly starts producing mycelium, which is the vegetative state and often has a fuzzy, chalk-like appearance. Chalkbrood mummies (Photo credit: USDA-ARS)
Photo by: Nadine Chapman
The mycelium will start to engulf the larva, transforming it into what is often referred to as a "mummy.” The fungus will out-compete the host for nutrients and will eventually kill the larva, typically when it is in the upright stage. Once the larva is completely mummified, the mycelium starts to harden and transitions in color from white to gray and then finally to black - the most infectious stage. When inspecting a honey bee colony, these Chalkbrood mummies can be found in both capped and uncapped cells. If the infection is widespread in a colony, a beekeeper can pick up a brood frame, shake it and the mummified larvae will move around in their cells making a rattling noise. Fortunately, infected larvae can easily be removed from a frame by tapping it on a hard surface.
Based on the symptoms Chalkbrood exhibits, it is very easy to diagnose this disease through a visual inspection - therefore there's no need to collect a sample for lab analysis in order to make a positive identification. In addition to the mummification of larvae, the brood pattern will also look spotty. However, there are many causes for a spotty brood pattern, so never use that as the only evidence of this disease, or any other for that matter. Chalkbrood is typically spread between hives by drifting bees, but can also be transferred during mating, feeding and robbing. Once the fungal spores infect a nurse bee, they are quickly transmitted to the developing larvae.
There are several preventative measures beekeepers can implement to ensure that Chalkbrood does not affect their hives. As with many other pest and disease issues, maintaining strong and healthy colonies is a key preventative technique. If there is a strong worker population in a hive, then they are able to remove the mummified larvae, thus preventing the disease from spreading further. As a result of this behavior, a beekeeper will typically find the Chalkbrood mummies on the bottom board or outside the entrance of the hive. Other methods of prevention include the sanitation practices of maintaining clean beekeeping equipment and removing any old comb from hives - especially if symptoms of Chalkbrood were present in the past.
Protecting the hives from stressors, such as lack of forage or nutrition, exposure to agrochemicals, and presence of other pests and diseases, will also help the bees defend against a Chalkbrood infection. Finally, requeening colonies with hygienic stock is another tool a beekeeper can use to protect against this disease.
Providing upper ventilation in the hive also helps prevent Chalkbrood. Since the Chalkbrood fungus thrives in damp environments, cracking the lid of the hive will provide enough airflow to prevent moisture from accumulating. A small stick, a pencil, or a popsicle stick placed between the top box and the lid will provide just enough space for air to flow and wick moisture away. Also, requeening or providing some sort of brood break will help reduce the infection. *Currently, there are no chemical treatments approved for controlling Chalkbrood.
Healthy brood vs Chalkbrood infected brood Photo Credit (USDA)
When I first started keeping bees, no one told me that I would have to become knowledgeable in biology, epidemiology, nutrition, genetics, botany and chemistry in order to maintain my hive. I just wanted to see my bees grow and make some honey! I learned very quickly that in order to see these results I had to have a good grasp on all of the factors that make a hive healthy and successful. Understanding the basics of the different honey bee pests and diseases and how they interact with a colony is one of those key factors. Now that you are an expert on Chalkbrood, you are one step closer to being the best caretaker of your bees!
by: Mary Reed Texas Chief Apiary Inspector Entomologist - Secretary, Apiary Inspectors of America Texas Master Beekeeper Program Manager