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Bee diseases

The honeybee is susceptible to all kinds of diseases. The Varroa mite is a major threat to the European honeybee. Brood diseases such as American foulbrood (AFB) and European foulbrood (EFB) affect honeybees in the larval and pupal stage. Nosema is a disease that is caused by a unicellular parasite.Viral diseases such as Deformed Wing Virus (DWV) and Chronic Bee Paralysis Virus (CBPV) are often latent in bee colonies. Ranging from pollen mites to wax moths, they all benefit from honeybees in one way or another.

Varroa destructor

Varroa mite disease (varroatosis) is caused by the ectoparasite Varroa destructor. This exotic parasite is a major threat for the European honeybee. There is consensus about the multifactorial cause of bee mortality, but the presence of this mite in all bee colonies leads to enormous pressure on the health of the colonies.

Small Hive Beetle

The Small Hive Beetle (Aethina tumida) has recently been introduced in Southern Italy in the province of Calabria. This species, new to Europe, parasitizes bee colonies with damaging effects.

Brood diseases: American foulbrood (AFB), European foulbrood (EFB) and Chalkbrood

Brood diseases affect honeybees in the larval and pupal stage. Although these diseases do not usually lead to the mortality of a colony, they can constrain its development. Bees can escape from brood disease by swarming and by actively abandoning the brood. If a beekeeper represses or disturbs these mechanisms, brood diseases can threaten the existence of the colony.

American Foulbrood: Using a matchstick to pull a ropy thread.
American Foulbrood: Using a matchstick to pull a ropy thread.

Bee colonies are affected by brood diseases resulting from bacteria, fungi, viruses and mites. Brood diseases impact the health of individual larvae and pupae, often resulting in mortality. Serious infections can affect much of the brood, which can ultimately slow the growth of a bee colony. Brood diseases can be exacerbated by poor conditions for bees, such as bad weather and lack of food.

American foulbrood (AFB) and European foulbrood (EFB)

Important bacterial diseases are American foulbrood (AFB) and European foulbrood (EFB). These brood diseases are extremely contagious and difficult to eradicate. Their control requires radical intervention by the beekeeper. American foulbrood is a notifiable disease; a suspected outbreak must be reported to the competent authority. However, the government does not have the obligation to actually control the disease. This remains the task of the beekeepers.

European Foulbrood: The dark crusts in the open cells are dried up larvae infected with EFB. Some larvae die after the cell is sealed. The cappings of these cells are opened by workers in order to remove the corpse (perforated cell at the bottom of the image). in the top left corner a chalk brood mummy can be seen.
European Foulbrood: The dark crusts in the open cells are dried up larvae infected with EFB. Some larvae die after the cell is sealed. The cappings of these cells are opened by workers in order to remove the corpse (perforated cell at the bottom of the image). in the top left corner a chalk brood mummy can be seen.

Chalkbrood

Another important brood disease is chalkbrood. This fungal diseases changes infected larvae and pupae into mummies. It often occurs during long spells of wet and cold weather.

Chalk brood mummies in a brood frame
Chalk brood mummies in a brood frame

Diagnostics

Wageningen Bioveterinary Research conducts tests for the diagnostics of American foulbrood. Read further on our diagnostics page.

Viruses: Deformed Wing Virus (DWV) and Chronic Bee Paralysis Virus (CBPV)

Most viral diseases are latent in bee colonies and are rarely a problem. However, viral infections can be exacerbated by stressful situations and can then have serious consequences for bees. Since the introduction of Varroa destructor in 1983, a number of viruses have started to play a more prominent role in the health of bee colonies.

At least 23 viruses are known to be associated with the genus Apis (De Miranda et al. 2012; Runckel et al. 2011; Bromenshenk et al. 2010). In general, viruses are latent in honeybee populations and cause little or no damage to bee colonies. However, virus replication may be stimulated or activated (usually in stress situations), resulting in the emergence of disease symptoms. This can cause incidental damage or even colony mortality.

Deformed Wing Virus (DWV)

An exception to this rule is the Deformed Wing Virus (DWV). Due to the introduction of Varroa destructor, this virus has become a serious threat (Martin et al. 2012) and is now a structural problem for the health of honeybees. It is primarily caused by the effective transmission of DWV by Varroa mite; the virus also replicates in Varroa mites. In addition, Varroa mites cause an immune response when they feed on bees. This immune response activates the replication of virus particles in bee tissue. DWV can cause physical symptoms such as deformed wings, which in turns affect bee lifespan.

Deformed Wing Virus (DWV)
Deformed Wing Virus (DWV)

Chronic Bee Paralysis Virus (CBPV)

During long, cold periods in the growing season, the Chronic Bee Paralysis Virus (CBPV) can become a problem. This virus causes paralysis. Bees infected with this virus can be identified by their black colour and their lack of hair.

A honey bee infected with CBPV (Chronic Bee Paralysis Virus) resides on a honey bee comb. Symptoms include hair loss and blackening, but also trembling.
A honey bee infected with CBPV (Chronic Bee Paralysis Virus) resides on a honey bee comb. Symptoms include hair loss and blackening, but also trembling.

Other viruses

Viruses are receiving increasing attention because the techniques to detect viruses have improved, providing more insight into the role they play in the health of bees. In relationship to bee mortality, Bees@wur is also conducting research into:

Which viruses are present in Europe?

Virus Distributie EU
Acute Bee Paralysis Virus (ABPV) +
Kashmir Bee Virus (KBV) +
Israeli Acute Paralysis Virus (IAPV) +
Black Queen Cell Virus (BQCV) +
Deformed Wing Virus (DWV) +
Varroa destructor Virus 1 (VDV-1) +
Sacbrood Virus (SBV) +
Slow Bee Paralysis Virus (SBPV) +
Chronic Bee Paralysis Virus (CBPV) +
Cloudy Wing Virus (CWV) +
Bee Virus X (BVX) +
Bee Virus Y (BVY) +
Arkansas Bee Virus (ABV) ?
Berkeley Bee Virus (BBPV) ?
Macula-like Virus (MLV) +
Fliamentous Virus (AmFv) +
Apis Iridescent Virus (AIV) ?
Aphid Lethal Paralysis virus (ALPV) ?
Big Sioux River virus (BSRV) ?
Lake Sinaï Virus 1 (LSV1) ?
Lake Sinaï Virus 2 (LSV2) ?
Invertebrate Iridescence Virus (IIV) ?
Kakugo Virus ?

Nosema apis and Nosema ceranae

Nosema is a disease that affects adult honeybees. It is caused by a unicellular parasite. The parasite lives on the tissue in the midgut. Nosema is prevalent world-wide. The disease also occurs frequently in the Netherlands and Belgium. Nosema apis can cause substantial damage. Since 2008 Nosema ceranae has also been present in the Netherlands. This species, probably an exotic, is present in virtually all bee colonies, but it is unknown how and whether it causes disease or mortality in bee colonies in the Netherlands.

Nosema spp. sample taken from a honey bee's abdomen (100x, microscope). The spores are recognizable as elongated, rounded shapes, often compared with the shape of rice grains. The round cells in this image are amoeba (Malpighamoeba mellificae). The three larger dark blobs in this image are pollen grains.
Nosema spp. sample taken from a honey bee's abdomen (100x, microscope). The spores are recognizable as elongated, rounded shapes, often compared with the shape of rice grains. The round cells in this image are amoeba (Malpighamoeba mellificae). The three larger dark blobs in this image are pollen grains.

Only in host cell

Nosema apis and Nosema ceranae are Microsporidia. Microsporidia are obligate intracellular parasites. This means that they cannot live and reproduce outside the host cell. Microsporidia live in cells of insects and other invertebrates. Quite recently, Microsporidia parasites were also discovered in humans (Barbancon 2007).

Mostly in cold and rainy periods

Nosema apis usually strikes in the spring. Long-lasting cold and rainy periods can result in insufficient pollen being produced; as a result bees become susceptible to this intestinal parasite. This can lead to mortality and dysentery. The symptoms of Nosema infestation are also characterised by the presence of dead and cramped bees inside and in front of the hive.

Surviving outside of the cell

The lifecycle of Microsporidia includes the spore stage, during which the parasite can survive for long periods outside a cell. The spread from cell to cell and from one organism to another takes place in the spore stage.

March, during spring inspection a Nosema apis infected colony was detected. Clearly visible are the feaces on the comb. Approx. half the adult population had died and was found in fornt of the hive and on the bottom. The symptoms of Nosema apis distinguish this species from Nosema ceranae.
March, during spring inspection a Nosema apis infected colony was detected. Clearly visible are the feaces on the comb. Approx. half the adult population had died and was found in fornt of the hive and on the bottom. The symptoms of Nosema apis distinguish this species from Nosema ceranae.

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Tropilaelaps mite

The genus Tropilaelaps consists of 4 species: T. clareae, T. koenigerum and the recently described species T. mercedesae and T. thaii. Their original host was the giant honeybee (Apis dorsata), but Tropilaelaps can also occur in colonies of other bee species. Both T. clareae and T. mercedesae have been observed in Europe and they can reproduce in European honeybees (Apis mellifera). Tropilaelaps has not been observed in the Netherlands.

The lifecycle of Tropilaelaps spp. in Apis mellifera colonies is comparable with the lifecycle of Varroa destructor. Under normal conditions, 1-4 adult mites enter the brood, each of which produces 1 to 2 offspring. The mites have a preference for drone brood over worker brood (ratio: 3:1). Equal numbers of males and females are produced. When a young bee emerges, the adult female mites also leave the brood cell. The immature offspring and males remain behind and die. The mites remain on the adult bees for no more than two days before they again enter the brood cell to reproduce.

Acarapis mite

Acarapis mites (Acarapis woodi) are parasites that attach themselves to the first pair of trachea (breathing tubes) of the adult honeybee. The queen, workers and drones can all become infected.

The mite is miniscule: 85-116 μm long and 57-85 μm wide, is yellow-white in colour and has eight legs. The mouthparts, with a piercing/sucking mechanism, are powerfully developed. The mite probably produces a substance that weakens chitin, to make piercing easier. The first pair of legs contains the organs of touch.

Microscopic image of tracheal mites (Acarapis woodi). The structure on the left is part of a tracheal tube of a honey bee.
Microscopic image of tracheal mites (Acarapis woodi). The structure on the left is part of a tracheal tube of a honey bee.

Amoebic diseases

The amoeba Malpighamoeba mellificae Prell belongs to the group of unicellular animal-like organisms, the Protozoa. These protozoa move by means of pseudopodia (false feet) and feed by phagocytosis.

Malpighamoeba mellificae can form cysts. These cysts have a highly resistant cell wall; they are spherical with a cross-section measuring about 7.5 μm. When the cysts, which are consumed by the bees with their food, reach the rectum of the bee, the amoebae are released. They crawl back through the small intestine into the Malpighian tubules, where they multiply and eventually form cysts once again. These cysts are then excreted with the faeces.

The amoebae damage and clog the Malpighian tubules. As a result, metabolic waste products build up and become toxic to the bee. They also disrupt the bee's water balance, causing dysentery.

Malpighian tube of a honey bee with amoeba (100x)
Malpighian tube of a honey bee with amoeba (100x)

Wax moths

Experienced beekeepers have a basic rule of thumb: be careful when storing honeycombs and hive material. And there is a reason for this! Wax moths can completely devour stored honeycombs. They can even destroy the wooden frame! By themselves, wax moths are not a threat for honeybees, but in weak colonies they can eat their way through the honeycombs.

Greater Waxmoth (Galleria mellonella). A few box of frames unattended for a few months can be a feast for wax moths.
Greater Waxmoth (Galleria mellonella). A few box of frames unattended for a few months can be a feast for wax moths.

'Bee louse' - Braula coeca

The common name for Braula coeca is the bee louse. In reality, it is a wingless fly that is entirely dependent on honey bees for its survival. The bee louse no longer occurs in the Netherlands. This species probably disappeared due to the introduction of the Varroa mite. The products that are used to control the Varroa mite are harmful for this commensal organism. 

Bee louse (Braula coeca)
Bee louse (Braula coeca)