Bee pests and Pathogens

The health of honey bees is influenced by numerous factors. In addition to the Varroa mite, the bee colony may be decontaminated by numerous other pathogens:


Nosemosis (also called nosema) is caused by a single-celled fungus parasitic disease in honey bees. It is the most common animal disease in adult bees and highly contagious.


The cause of the disease, Nosema apis and Nosema ceranae, are single-celled fungus, parasites belonging to the group of small sporozoans. The bees ingest the spores via food and at watering places and while cleaning the honeycomb or through other hive parts. A few spores can already lead to an infection. After ingestions, the spores enter the abdomen of the bee and create a considerable destruction to the intestinal epithelium, which greatly reduces the bee’s metabolic activity.

The pathogen, originally occurring in the Eastern honey bee, Nosema ceranae, was also detected in the Western honey bee in 2005 for first time. Ever since, Nosema caranea has been spread throughout Europe. Especially in Spain, Nosema ceranae is widespread and causes high losses of bees.

Due to unfavourable factors, frequently occurring in the spring, such as bad weather, inadequate pollen supply or an unfavourable bee site, the outbreak of Nosema apis occurs.

Both pathogens cause serious intestinal diseases and may lead to a shortened life span of adult bees. A characteristic of infection with Nosema apis are brown or yellow brown excrement stains inside the beehive and on the honeycombs. However, in Nosema ceranae infections, the described typical symptoms are lacking. Here, the main symptom of the disease is visible through the slowly declining number of bees in the beehive.

The transmission of Nosema apis to other colonies can occur through contaminated combs or the beekeeper’s equipment, as well as robbing and flying to the wrong hive through individual bees. The disinfection of the existing hive and honeycomb material and the beekeeper’s tool plays an important role in the outbreak of the disease.

American Foulbrood

The pathogen of the American foulbrood, Paenibacillus larvae, creates very resistant spores that infect only the honey bee larvae through ingested food. With the food, the spores enter the abdomen and then penetrate the intestinal epithelium to rapidly multiply in other tissues of the larva. The brood dies in the stretched larva or pre-pupal stage and in the capped cell.

American foulbrood

Only then, the typical symptoms of the infectious disease become apparent. They consist of discoloured, sunken, often holey cell covers and the stringy mass that remains in the brood cell eventually dries to scales. With the so-called match stick test, in which the honeycomb content sticks to the match like a thread, and an inspection of the cell cover, the disease can be detected among other things.

The disease is spread by physical contact and social exchange of food in the hive. The chain of infection can only be broken, if the infected larvae can be detected and removed by the bees before the new sporulation. However, since hygiene behaviour and the ability to remove spores from the honey stomach are different from race to race, the course of the disease differs considerably in various colonies. In general, the increasing brood infection becomes weaker and dies sooner or later.

Due to bees that rob honey, fly to the wrong hive, or swarm, the pathogen of the American foulbrood is spread to other colonies. The disease can spread even through the exchange of brood and food combs, as well as hives and equipment.

American foulbrood is a highly contagious disease and should be treated as soon as possible and comprehensively in accordance with the country-specific recommendations and legal regulations.

European Foulbrood

The pathogen of the European foulbrood, Melissococcus plutonius, is ingested by the larvae with food. Larvae can survive a mild infection. However, due to toxins released by the bacteria, they often die in the larva stage or shortly after the capping. Then, the dead brood has a typical foul smell.

In an infected bee colony, there can be a balance between reproduction and elimination of the pathogen over years. On one hand, the bees transmit the pathogen with the contaminated food to the brood, on the other hand, they remove it with the cleared brood and the cleaning of the cells. This way, the hygienic behaviour of bees has a significant impact on the progression of the disease.

The sick and weak colonies are frequent targets of raider bees. The food can cause a massive infection. If the colony is not able to heal itself, stimulative feeding can stimulate the bee’s drive to clean. It is also recommended to replace the most infected brood combs. Cleaning of the honeycomb during the breeding period can also be achieved by raising a new queen.

For mildly infected colonies, the treatment method is to add honeycombs with open brood. In this case, due to the increased demand for food from infected larvae, there is initially also a lack of food. The bees recognise that and, as a result, they clear out the brood.The best prevention against the European foulbrood is to make sure there is a good nectar production. This ensures that the bees maintain their hygiene behaviour and cope with the disease.


The chalkbrood is a fungal disease that infects honey bee larvae with the pathogen Ascosphaera apis. The young bee larvae are penetrated by the fungus, which leads to holes in the brood area, and the brood dies in the stretched larva or pre-pupal stage. The infected brood is loose in the cells and when rotated, it falls out of the honeycomb.


Depending on the growth of the fungus, the mummies are white to grey-black and have a spongy to hard consistency. The spores of the fungus are distributed by the bees, honeycombs and through draft and can infect young larvae again and again. They are very resistant and can remain infectious for up to 15 years in an unoccupied hive or in an infected colony.

The chalkbrood requires, as all of fungus diseases, a humid and cold climate for their development. In general, a healthy bee colony is able to maintain the most favourable climate of about 35 degrees Celsius and about 60% humidity for its beehive, by either the cooling or warming the brood nest. A weakening of the colony by other diseases can cause this climate to collapse. For this reason, only strong and vital colonies should be maintained at that level. During the selective breeding, a pronounced drive to clean must also be ensured, and the colonies should have only so much space as they are able to occupy.

With a genetically lower degree of breeding hygiene behaviour of bees, it helps to replace the old queen with a new pure-bred queen. Colonies with a higher degree of breeding hygiene recognise the damage already with bee larvae, hence, this characteristic does not allow the development of any chalkbrood mummies. The pathogen cannot spread.

Small hive beetle

Small Hive Beetle

Although the small hive beetle (Aethina tumida) is only 5 mm long, it is one of the most feared bee parasites because with a heavy infestation, it can destroy an entire colony within a very short time. Compared to the African subspecies, which have developed control mechanisms as the original host of the hive beetle, the European subspecies are unlikely to achieve this.

Small Hive BeetleThe small hive beetle (Aethina tumida) came originally from Africa, south of the Sahara. Since 1998, it has been unintentionally introduced to the United States, Canada, Mexico, Jamaica, Australia and Cuba, and has spread and caused tremendous damage there. In 2004, the beetle was first discovered in Europe, in Portugal, during a delivery of queen bees and it was successfully destroyed. Unfortunately, the small hive beetle reached Italy in 2014 and has rapidly spread there ever since.

In its original homeland of Africa, the small hive beetle is considered a rather harmless pest. The African honey bees have developed defence mechanisms. Compared to their European cousins, they find infested brood cells faster and clean their stock more thoroughly, before they swarm. This takes away the bug’s basis for nutrition and multiplication.

Areas to where the beetle has spread Live hive beetle

Areas where the beetle have spread

In addition, the African honey bees confine the small hive beetle in a stable prison that they built from the collected bee glue, the so-called propolis. Even the guard be is placed there to monitor the enemy. This is how the honey bees fight the voracious beetle, however, the beetle has also learned from that: The beetle imitates the behaviour of begging bees to obtain food, which allows it to survive in its prison for up to two months. Luckily, it cannot mate and multiply under these conditions.

After the beetle was able to enter the beehive, it lays his eggs in a protected hiding place, which cannot be accessed by the bees. After two to six days, the hatched larvae feed on honey, beeswax and pollen, and destroy the structure of the comb: The honey spoils and is no longer edible. Some bee colonies even leave the infested hive in an emergency swarm.

The pupatation of the beetle takes about 3-4 weeks and takes place in the soil below or near the hive. Since the pupation is highly dependent on the temperature and humidity of the soil, the duration can vary significantly.

Other things that make this quickly-multiplying beetle dangerous for colonies: It can fly very well, and travels distances up to 20 kilometres, allowing a rapid spread. Currently, there are almost no control methods available.

The most important protective measures to keep the beetles as well as other dangerous pests and diseases away, was the introduction of strict import regulations for honey bees from abroad. Nevertheless, if the beetle shows up in Europe, there is currently only one solution: The beekeeper must report the parasite because in the EU, the small hive beetle is by law a pest that must be reported. This means that the beehives must be closely monitored. Because in the case of a plague, there is only one chance to eradicate the beetle: catch it early enough. It cannot be done once it is well established.

Asian predatory wasp, vespa velutina

Asian predatory wasp

Another flying enemy for the Western honey bee is the Vespa velutina, a species of hornet indigenous to Asia. One recognises the mostly black hornet by its broad orange stripes on the abdomen and the fine yellow band on the first segment. Experts fear a prolonged disruption of the ecological balance, if the approximately two centimetre long insect continues to multiply.

Although the hornets are not more aggressive than their European cousins, and hardly dangerous to humans, but honey and wild bees can suffer from it. Because the hornets build their new colonies usually close together, the concentration of nests per area is very high, and the pressure on potential hive insects increases. And honey bees are already on the hornet’s menu.

Vespa velutinaCopyright: Karine Monceau

In Europe, the hornet was found for the first time on the Atlantic coast of France in 2004. From there, it has conquered the European continent. It has been sighted in Spain in 2010, one year later in Portugal and for the first time in South-West Germany in 2014.

In their homeland, the Asian honey bee colonies have developed a strategy to eradicate the enemy in the hive: They approach the hornet in large numbers, form a veritable ball around it, and heat immediate vicinity of the enemy to almost 50°C. The bees can briefly withstand the high temperatures, but the hornet dies from it. Since the Western honey bees have not been threatened by the Vespa velutina until very recently, they have not yet developed such defence mechanisms. Currently, the lifestyle of the Asian hornet is being examined in more detail. Other measures are also examined to prevent further spreading.

Until then, the beekeeper can protect their bees especially if they seek refuge in the beehive: Install a grid in front of the entrance, that doesn’t allow larger hornets to slip through.

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