Bee Diseases

bee diseases varroa brood
Brood infected by wax moths

Bees are susceptible to illness and diseases like any other living thing. However, one sick bee can cause irreversible damage to a colony as the disease spreads. Additionally, parasites target certain bees and shorten their lifespans. 

Diseases are a troubling problem for beekeepers trying to maintain healthy hives, but there are ways to treat and prevent them.

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    Common Diseases That Kill Bee Larvae

    Many viruses, fungi, and parasites can affect bees and create problems for colonies and beekeepers. Understanding how to recognize, treat, and prevent these diseases is paramount for having a healthy, well-managed colony. 

    American Foulbrood 

    American Foulbrood is a bacterial disease caused by the bacteria Paenibacillus larvae, a gram-positive, spore-forming bacteria. It is often recognized as the worst of honey bee diseases. Because the spore form can sit dormant for years, it’s highly contagious. 

    Just a few spores can wreak havoc on healthy hives, and the effect is likely the death of the colony. If a colony is affected, proper precautions are required because the spores can persist on equipment for years, even with below freezing temperatures and other environmental factors.

    This disease is spread from bees to larvae, which causes most pupae to die. The larvae receive it from worker bees feeding them, which releases the spores into the larvae’s mouth through regurgitation. The spores become active and reproduce in the larvae, and the larvae then die with millions of infected spores in them.

    American Foulbrood infestation looks like cells covered with dark cappings. This disease can escalate quickly and may be passed on to other hives. At that point, beekeepers need to burn affected colonies and any potentially exposed materials, bury the ashes, and sterilize any equipment. 

    European Foulbrood 

    European Foulbrood (EFB) is a far less contagious disease than its counterpart, American Foulbrood, for the causal bacteria of EFB, Melissococcus plutonius, does not form spores.

    EFB manifests in larvae digestive systems and robs the larvae of food, causing them to die from malnutrition and starvation. It can affect a colony more heavily than American Foulbrood and worsen in cold weather. 

    EFB infestation looks like deformed, shrunken, yellow and white larvae in cells, and the comb may have a spotty pattern. 

    If an infection is suspected, the hive is treated prophylactically with antibiotics. Other measures can be taken, such as adding more frames with healthy larvae to decrease the amount of food going to the infected larvae. Beekeepers can also make dietary changes or use a shock swarm method to transfer the colony to new combs.

    Fungal Diseases

    Fungal organisms can lead to mass death within a bee colony if not prevented or handled well. 


    Chalkbrood is a mild fungal disease that can kill young larvae but does not affect adult bees or pupae. It is caused by the fungus Ascosphaera apis, and it is known for causing “chalkbrood mummies,” or mummified larvae that fill the brood cells. Worker bees will uncap their cells and reveal the dead larvae. Later, the bees will dispose of them. 

    This fungus is often found in wet spring conditions, and it enters new colonies by drifting bees. Antifungals are not used to treat it, but beekeepers who follow general protocol in maintaining healthy hives can prevent chalkbrood. Other measures can be done, such as replacing the queen with one that is more resistant to the fungus. 


    Stonebrood is a fungal disease caused by various types of Aspergillus fungi. It is generally asymptomatic unless the colony is already unhealthy. 

    The fungus is spread through eating or contact, and it targets larvae, pupae, and adult bees. It can result in larvae mummification like chalkbrood, but with stonebrood, they appear in varying colours, such as white, green, and yellow, based on the Aspergillus type. The larvae become hard and stone-like. If an adult bee is infected, it will become paralyzed and die, generally away from the hive.

    Most of the time, stonebrood can be naturally passed and overcome by a hive, but if there is a very mouldy comb, it should be removed and the honey or wax should not be used for humans. The best way to prevent stonebrood is through good beekeeper management strategies, such as replacing a third of combs yearly. 

    bee diseases
    Wax moth infestation



    Sacbrood virus infects female larvae, those maintained to become workers, and adult bees. The virus spreads through food and settles in the larvae. Once infected, the virus expands within larvae’s bodies and causes them to raise their heads in their cells. They die and can turn yellow or brown. The dead larvae may seep viral fluid that spreads through the colony. 

    Adult honey bees infected with Sacbrood are asymptomatic but may display unusual behaviour like foraging without collecting pollen. The virus lifespan can be as long as four weeks and spreads easily through pollen and food. 

    Bees will dispose of dead larvae and may not catch the virus. If the workers are unable to contain it, beekeepers may add worker bees, provide food, or re-queen the colony. 

    Adult Bee Diseases

    Different pests target larvae, but some prey on adult bees. This can cause colony collapse disorder as worker bees become disabled and unable to contribute to a hive’s food replenishment and hygiene. 

    Cloudy Wing Virus 

    Cloudy wing virus can be a product of a varroa mite infestation within a colony. Varroa mite is considered to be the primary vector for the cloudy wing virus. The virus weakens bees’ wings, which makes them ineffective. Bees do not survive long without working wings. 

    Beekeepers are advised to burn the entire colony and infected combs.


    Parasites and pests are organisms that use others to survive and populate. There are a number of parasites that use honeybee hives to eat and reproduce in. 

    Wax Moth 

    Wax moths are parasites that like to eat beeswax from hives. The wax moth larvae burrow into beehives and start eating through cell caps that house pupae. Pupae that prematurely lose their cappings can end up deformed as adults. 

    Developing larvae will cocoon themselves in combs or hives and weaken the structure. As adults, they stop antagonizing bee colonies, as they no longer feed on beeswax. Beekeepers will use different solutions to clean combs of wax moth larvae and pupae. 

    Varroa Mite

    Varroa mites consume bee larvae as well as bring in viruses, some of them being deformed wing virus and cloudy wing virus. These mites cannot live without honeybees, and they weaken hives in the process. The mites are minuscule, tick-like, reddish-brown parasites that cling to bees’ bodies.[5] Mature female mites can also survive as the larvae become adult bees. 

    Varroa mite infestation causes deformity, slowness, and death of bees, but they are present at some level in nearly all hives in the US. If the drone cells appear to be heavily infected, then treatment with miticides should be performed. 

    Beekeepers should use various strategies to monitor the mite population within the hive and make sure they stay below a manageable threshold. Some bee strains are more likely to groom off the mites, so another possibility is replacing the queen with a type more resistant to the mites.

    Nosema Disease 

    Nosema is a parasitic microorganism that thrives in bees’ digestive systems. Nurse bees that are affected do not develop properly, and if the queen gets infected, she may die early. Nosema is thought to be related to colony collapse disorder. 

    The disease is passed from infected bees in their excrement, and the spores can stay infectious over the winter months. Then when the overwintered bees clean the combs in the spring, the organisms can spread rapidly and cause a quick population decline. However, most colonies survive and recover in the warmer months when the bees’ excrement is dropped outside the hive. 

    Another species of nosema was recently shown to cause most nosema infections in the US, and this species causes infection predominantly during the summer season.

    Managing nosema infections can involve antimicrobial treatment with fumagillin, replacing older queens, decreasing hive stress, and taking precautions to not spread the spores to other hives.

    Tracheal Mite 

    Tracheal mites affect bees’ respiratory systems by multiplying in the trachea. The female mites lay eggs in the bee’s trachea, and then when the eggs become mature mites, they exit the trachea and latch onto a hair. Within the next day, the mite must then find another host to enter and lay eggs. 

    Symptoms of tracheal mite infestation are shortened lifespan, inability to fly, and wing deformity. The most susceptible times are during the winter and then the early spring when most of the bees are older. Colonies can succumb to these mite infestations and collapse. 

    Detecting tracheal mites is challenging and requires microscopic evaluation of the bee trachea. Beekeepers do become concerned when colonies’ population drops or bees exhibit strange behaviour such as excessive swarming. Although this may not equate to mite infestation, it can indicate that something is wrong within the colony. 

    The treatment for tracheal mites is menthol, which can be used as a fumigant that kills the mites but does not damage the bees. It’s also beneficial for beekeepers to use menthol crystal packets placed in the hive during the fall. Vegetable shortening sugar patties placed in the fall and/or spring can also help with mite control by disrupting their life cycle. 

    bee diseases varroa
    Varroa Mite feeding on larva

    Isle of Wight Disease 

    Beekeepers have historically referred to tracheal mite infestations as Isle of Wight disease. This is because the tracheal mite was believed to be the cause of the 90% bee colony losses on an island in the English Channel in 1919.

    Because of these major losses and the spread of disease to Europe, the US tightened restrictions on bees by banning the import of bees from Europe. The cause of the Isle of Wight disease was not fully identified, but tracheal mites and nosema are often given as possibilities.

    Amoeba Disease 

    Amoeba disease is invisible and asymptomatic. Like tracheal mites, they’re microscopic and undetectable. This disease is still not completely understood, but scientists are aware that it can cause dysentery and short lifespans. 

    Colony Collapse Disorder 

    Colony collapse disorder can be the result of the virus and parasitic infestations within hives. Additionally, ill-kept colonies are easily susceptible. External factors like pesticides and transportation can cause this disorder. 

    Colony collapse refers to colonies with an unbalanced ratio of worker bees to larvae or food. Hives with this disorder may have an overabundance of honey and nectar, but not enough worker bees to feed it to the growing larvae. 

    This disease has consequences beyond the hive. The lack of worker bees in the ecosystem affects pollination around the world and may result in crop decline. 

    Beekeepers should avoid pesticides and maintain hygienic surroundings to allow worker bees to heal and complete tasks. 

    Parasitic Mite Syndrome

    Parasitic mite syndrome may look like a fungal or viral disease since it affects bee larvae. Researchers correlate this syndrome with varroa mites, but the exact cause is unknown. Bee colonies will drop in population in both adult bees and larvae. 

    The adult bees may develop malformed wings and other deformities due to disturbed development from mites during their larvae stage. 

    bee diseases brood infected
    Dead bees in the comb cells caused by disease

    Can Bees Spread Disease to Humans?

    With the number of illnesses beehives can encounter, it’s understandable to question whether bee disease can spread through honey. There has been no known instance of bees transmitting diseases to humans, however.

    Stonebrood is caused by Aspergillus, and this fungus causes respiratory disease in humans. It is also a known carcinogen. While the transmission is unlikely, infected products should be disposed of and not be used for human consumption.

    Just Like Humans, Bees Fight Pests and Diseases Daily

    Common diseases like foulbrood, as well as other fungal diseases, like chalkbrood and stonebrood, can prove problematic for entire colonies. Pests such as wax moths, varroa mites, tracheal mites, and others can be equally as problematic and result in foundational damage to the beehive. 

    It is essential to maintain good beekeeping practices and regularly monitor for disease to prevent disease spread and mitigate the risks to hives. 

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