Diseases and Pests

The most asked question in beekeeping is probably “How can we fight diseases and parasites?”

Contrary to conventional bee keeping, the answer is not a soup of chemicals to be sprayed in the hive. The answer is simply to have a healthy colony. In order to help our colony fight the diseases and pests, first we need to understand how the diseases and the pests work. That’s why before recommending any treatment, we will look into the origination and the cause of the diseases.

In ecological beekeeping, we always need to keep in mind that application of chemotherapeutic measures such as antibiotics always risks the danger of residues. Therefore for the goodness of the bees, the honey and the environment, we should always resort to the most natural and the least invasive remedies.

The effective defence against disease is one of the most essential achievements of the bee colony. The individual bee’s immune system functions in a similar way to that of vertebrate animals, although the most effective defence mechanism that can lead to self-healing of the bee colony is the social behaviour of removing as many pathogen agents or parasites as possible from the bee colony. This behavioural defence (entrance reduction and/or stinging) prevents parasites from penetrating the bee colonies, or their killing or removal. If the dead organism is too large to remove, as with mice, the bees completely cover it with propolis. This prevents release of the pathogens during decomposition of the body. Propolis is also applied inside the brood cells before new brood is reared.
Disinfection of the inside of the cell is effected by covering with secretion from the mandible and propolis. The most important defence against disease, however, is the bees’ hygiene behaviour. The defence against brood diseases comprises identification and removal of affected brood. To this end the bees inspect every single brood cell. On finding an infected larva in a sealed cell, the cell capping is removed, and any sick brood is removed and finally eliminated from the colony. The beekeeper recognises defence activities against brood diseases from the scattered brood surface. If adult bees fall ill they are either forced to leave the colony or are lost during the first foraging flight. Self-healing is therefore frequently possible by increasing flight activity. This may be initiated by foraging flights or during hibernation by cleansing flights, although it is only possible if the colony is sufficiently provided with pollen and nectar. Despite these very effective defence mechanisms, diseases, parasites and destructive insects may represent a problem for bee colonies.
Diseases may be spread by migration and sale of colonies, equipment and/or bees. With increasing globalization, bee colonies are transported over great distances and even between continents, in this way foreign species and their diseases are spread.

Bacterial Diseases

American Foulbrood Disease (AFB)

Beekeepers in temperate and sub-tropical regions around the world generally regard American foulbrood (AFB) as possibly the most destructive microbial disease affecting bee brood. The disease did not originate in, nor is it confined to, the Americas. It is widely distributed wherever colonies of Apismellifera are kept. In tropical Asia, where sunlight is abundant and temperatures are relatively high throughout the year, the disease seldom causes severe damage to beekeeping operations. The disease is contagious and the pathogenic bacterium can remain dormant for as much as and more than 50 years.

Cause:

American foulbrood disease is caused by a spore-forming bacterium, Paenibacillus larvae, which only affects bee brood; adult bees are safe from infection. At the initial stage of colony infection, only a few dead older larvae or pupae will be observed. Subsequently, if remedial action is not taken, the disease will spread within the colony and can quickly spread to other colonies in the apiary as a result of robbing, drifting workers, or contamination caused by the beekeeper’s hive manipulations. In the same way the pathogen agent can spread to other apiaries. Natural transfer mainly takes place within a radius of 1 km around the apiary. Often spores enter the bee colonies via foreign honey. Commercially available honey may be highly contaminated; therefore, special attention should be paid near honey processing enterprises and waste disposal sites.

Symptoms:

At the initial stage of AFB infection, isolated capped cells from which brood has not emerged can be seen on the comb. The caps of these dead brood cells are usually darker than the caps of healthy cells, sunken, and often punctured. On the other hand the caps of healthy brood cells are slightly protruding and fully closed. As the disease spreads within the colony, a scattered, irregular pattern of sealed and unsealed brood cells can be easily distinguished from the normal, compact pattern of healthy brood cells observed in healthy colonies. The bee brood affected by AFB is usually at the stage of older sealed larvae or young pupae, upright in the cells. Often therefore, a protruding tongue can be found with the rest of the body already decayed. At first the dead brood is dull white in colour, but it gradually changes to light brown, coffee brown, and finally dark brown or almost black. The consistency of the decaying brood is soft. Once the dead brood have dried into scales, the test cannot be used. The dry brood lies flat on the lower side of the cell wall, adhering closely to it – in contrast to sacbrood. This scale is usually black or dark brown and brittle. Often, a fine, threadlike proboscis or tongue of the dead pupa can be seen protruding from the scale, angling toward the upper cell wall.

Control:

In several countries, where apiculture includes large commercial operations, frequent, efficient inspection services are particularly advanced and a ‘search and destroy’ strategy may be adopted in an attempt to minimize damage to apiaries caused by this serious honey bee disease. The procedure involves hive inspections by qualified apiary inspectors. The entire honey bee population that is infected by American foulbrood is killed and hive materials belonging to the colony, are disinfected or destroyed by burning. The bees are usually killed by poisonous gas such as the burning of sulphur powder. All the dead bees, the frames, the supers, the honey and the contaminated equipment are thrown into a 1m x 1m x 1m hole in the ground. Kerosene is poured over the pile and set alight. When all the material has been completely burned, the hole is carefully filled in, to prevent worker bees belonging to healthy colonies from robbing any remaining contaminated honey. Although the above-mentioned method has proven effective, the practice of burning AFB infected colonies and equipment is costly, especially taking into account the high cost of beekeeping equipment. The destruction of brood combs and food combs is absolutely necessary as, apart from the bees, they are the main carriers of spores. Dry combs, without brood, can be preserved if an examination of wax samples in the laboratory does not reveal Paenibacillus spores. In which case the dry combs must also be destroyed. Old hives should be burned. Well conserved hives, however, should be disinfected. The inner part of a hive, once carefully cleaned, can quickly be singed out with the flame of a gas burner. The wooden surface should look slightly brownish. When this is not possible, e.g. if the hive is made from plastic, they should be cleaned and brushed with 3 to 5 percent sodium hydroxide. Before using other substances for disinfection you should make sure that no residues remain that could be dangerous to bees or the consumer of the processed honey. The killing of the bees can be avoided if the artificial swarm method is applied. A traditional method is to keep the bee colony in a dark environment for several days.

The bees are pushed into a decontaminated hive with new combs, the bee entrance is closed and they are placed in a dark preferably quite cool room. Within two days, the bees have used up the contaminated food. The colonies can then be placed either at their former stand or within a distance of at least 3 km away. If the bees are kept in the dark for three days they forget their old stand and can be placed anywhere. On the third day, however, some food shortage may occur. Therefore, the colonies should be fed. The direct artificial swarm method is less complicated. First, a clean, decontaminated hive is prepared. Instead of combs it contains three to six wooden bars, depending on the colony’s strength, provided with a wax strip as a starter for further comb construction. Using a queen excluder fixed at the entrance or above the bottom of the hive should prevent disappearance of the queen. The prepared hive is placed at the colony’s old stand subject to sanitation. Now the bees are pushed or brushed into the empty hive. Three days later, the combs that have been partially constructed by the bees are removed again and burned. Combs with midribs later replace these. Now sanitation is finished. The combs and the hive of the old colony are burned or decontaminated. In some countries, beekeepers who destroy their AFB-infected colonies receive compensation, either directly from the government or from beekeepers’ organizations.

European Foulbrood Disease (EFB)

As with American foulbrood disease, the name of this bacterial bee brood disease is inappropriate. The range of distribution of European foulbrood disease is not confined to Europe alone and the disease is found in all continents where Apismellifera colonies are kept.

Cause:

The pathogenic bacterium of EFB is Mellissococcus pluton. It is lanceolate in shape and occurs singly, in chains of varying lengths, or in clusters. The bacterium is Gram-positive and does not form spores. While many strains of M. pluton are known, all are closely related.

Symptoms:

Honey bee larvae killed by EFB are younger than those killed by AFB. Generally speaking, the diseased larvae die when they are four to five days old, or in the coiled stage. The colour of the larva changes at it decays from shiny white to pale yellow and then to brown. When dry, the scales of larvae killed by EFB, in contrast to AFB scales, do not adhere to the cell walls and can be removed with ease. The texture of the scales is rubbery rather than brittle, as with AFB. A sour odour can be detected from the decayed larvae. The clinical picture and the odour can vary depending on the kind of other bacteria involved (Bacillus alvei, Streptococcus faecalis, Achromobactereurydice). Another symptom that is characteristic of EFB is that most of the affected larvae die before their cells are capped. The sick larvae appear somewhat displaced in the cells.
When a scattered pattern of sealed and unsealed brood is observed in a diseased colony, this is normally an indication that the colony has reached a serious stage of infection and may be significantly weakened. However, this is the case with all brood diseases. EFB is transferred in the same way as AFB. Melissococcus pluton as a permanent form, does not form spores but capsules which are less resistant than the spores of P. larvae. The detection of M.pluton is normally carried out microbiologically.

Control:

The choice of an EFB control method depends on the strength of the infection, i.e. how many brood cells and combs are infested. If the infection is weak, it is often sufficient to stimulate the hygiene behaviour of the bees. Either they are placed at a good foraging site or they are fed with honey or sugar water. An even better result is achieved if the individual combs are sprayed with a thinned honey solution. If the infestation is stronger it makes sense to reduce the number of pathogens in the colony by removing the most infested brood combs. Empty combs or healthy brood combs then replace these. Since the bees’ hygiene behaviour is also genetically determined, replacement of the queen is also possible. Requeening can strengthen the colony by giving it a better egg-laying queen, thus increasing its resistance to the disease and interrupting the ongoing brood cycle giving the house bees enough time to remove infected larvae from the hive. In serious cases, the same methods can be used as for AFB. Sometimes chemotherapeutic measures such as antibiotics are called for, however, their application, always risks the danger of residues.

Fungal Disease

Chalkbrood Disease (Ascosphaerosis)

Cause:

Chalkbrood is a disease caused by the fungus Ascosphaeraapis. As its name implies, it affects honey bee brood. This fungus only forms spores during sexual reproduction. Infection by spores of the fungus is usually observed in larvae that is three to four days old. The spores are absorbed either via food or the body surface.

Symptoms:

Initially, the dead larvae swell to the size of the cell and are covered with the whitish mycelia of the fungus. Subsequently, the dead larvae mummify, harden, shrink and appear chalklike. The colour of the dead larvae varies with the stage of growth of the mycelia: first white, then grey and finally, when the fruiting bodies are formed, black. When infestation is heavy, much of the sealed brood dies and dries out within their cells. When such combs are shaken the mummified larvae make a rattling sound. In the laboratory the fungus can be identified by its morphology.

Control:

As with other brood diseases, the bees remove the infested brood with their hygiene behaviour (see European foulbrood), which is especially effective for white mummies. Though as soon as the fruit bodies of A. apis have developed, cleaning honey bees spread the spores within the colony by this behaviour. During the white mummy stage the fungus continues to develop at the hive bottom. If the mummies are not removed quickly, the spores may enter the brood cells carried there by circulating air. The beekeeper can stimulate the hygiene behaviour of the bees by changing the broodrearing conditions. In this respect, it is most important to adapt the size of the hive to the strength of the bee colony. In this way the bees have a chance to inspect and clean the many brood cells. Therefore, in most cases, the method of stimulating hygiene behaviour, already described under European foulbrood control, is sufficient for chalkbrood control. The beekeeper should ensure that the colony has a strong worker population, and that the hive is well ventilated and free from accumulated moisture. At early stages of chalkbrood infection, adding young adult workers and hatching brood, combined with sugar-syrup feeding, often proves to be helpful. Currently there is no known successful chemical control against chalkbrood. It means that chemical treatment shows a little effect to control chalkbrood. In most cases, commercialised substances only show a positive effect because they are sprayed, or fed with sugar water as described above.

Viral Diseases

The damage caused to colonies by viral infection varies considerably according to a number of factors, which include the type and strain of virus involved, the strength of the colony, weather conditions, the season and food availability. Basically, bees are well-protected against infection with their chitin body shell and gut coating. Parasitic mites sucking the blood of the bees, however, can penetrate this protection. Therefore, increased infestation by parasites is often accompanied by increased virus infection. Little known viruses such as Acute Paralyses Bee Virus (APBV), and Deformed Wing Virus (DWV) may become increasingly destructive in the future. As not much is known about the life cycle and pathogenity of most virus diseases, there are only a few ways to control them. Therefore, reflecting this situation, only the most widespread sacbrood is described.

Sacbrood Disease

Symptoms:

Field inspection to determine whether the pathogenic virus has infected a colonycan be easily carried out following symptomology. Diseased larvae fail to pupate after four days; they remain stretched out on their backs within their cells (distinct from the mostly twisted position of larvae affected by European foulbrood. The anterior section of the larva, consisting of its head and thorax, is the first part of its body to change colour, changing from white to pale yellow and finally to dark brown and black. On removing the larvae from their cell the inspector can easily observe that their skin is quite tough and that its contents are watery; the infected larva thus has the appearance of a small, watery sac. Dead larvae remaining within their cells eventually dry out to flat scales that adhere loosely to the cell floor.

Control:

No chemotherapeutic agent is effective in preventing or controlling sacbrood disease. Colonies often recover from the infection without the beekeeper’s intervention, particularly if the infection is not new to the geographic area. This mainly depends on the hygiene behaviour of the bees, which may be stimulated as with other brood diseases (see European foulbrood). Since the disease usually occurs when the colony is under stress (shortage of food, food-storage space, unfavourable climatic conditions such as damp during the rainy or cold season, unhygienic hive interior, poor queen, infestation with other diseases, etc.), the beekeeper should deal with severe cases by removing infected brood combs and taking other management measures to restore colony strength, such as providing food and adding worker population. If there is an extremely strong infestation it may be convenient to apply the artificial swarm method as for American foulbrood.

Protozoan Disease

Nosema Disease (Nosemosis)

Nosema disease is generally regarded as one of the most destructive diseases of adult bees, affecting workers, queens and drones alike. Seriously affected worker bees are unable to fly and may crawl about at the hive entrance or stand trembling on top of the frames. The bees appear to age physiologically: their life-span is much shortened and their hypopharyngeal glands deteriorate, the result is a rapid dwindling of colony strength. Other important effects are abnormally high rates of winter losses and queen supersedures. In climates with pronounced long periods of flight restrictions, i.e. no flight opportunities even for a day, the infection easily reaches a severe stage that visibly affects the strength of the colony. Less obvious infection levels in other climates often go undetected. The damage caused by Nosema disease should not be judged by its effect on individual colonies alone as collectively it can cause great losses in apiary productivity.

Cause:

The disease is caused by the protozoan Nosemaapis, whose 5 to 7 mm spores infest the bees, are absorbed with the food and germinate in the midgut. After penetration into the gut wall the cells multiply forming new spores that infect new gut cells or can be defecated. The nutrition of the bees is impaired, particularly protein metabolism.

Symptoms:

Unfortunately, there is no reliable field diagnostic symptom enabling a diseased worker bee to be identified without killing it, nor can the beekeeper recognize an infected queen. However, in severe cases of infection, it is sometimes possible to separate healthy from diseased bees, the abdomen of an infected worker often being swollen and shiny in appearance. On dissection, the individual circular constrictions in the alimentary canals of uninfected bees are clearly visible, while the constrictions cannot be seen clearly in diseased bees. Easy separation, after killing, of first abdominal segments with intestines attached, which shows white if strongly infected, versus a normal transparent, darker grey/ochre colour if there is no or only a low infection. The most reliable method of detecting Nosema disease involves laboratory procedures using a microscope for diagnosis. A simple diagnostic method used for adult workers is to use a sample of 20 suspected workers. The bees are killed, and their abdomens are removed and ground in water (2 to 3 ml per sample). A drop of the suspension of pulverized bee abdomens is then viewed under a microscope. If the disease is present, reasonably large individual bacilliform spores with bright, queen’s egg-laying capacity fluorescent edges will be observed. In the visual field of the microscope, at a 400 fold magnification, up to 20 spores indicate a weak, 20 to 100 a medium and 100 and more a severe infestation. In productive beekeeping, a healthy queen with a good egg-laying capability is always required, and Nosema disease in queens is therefore critical. The queen’s egg laying ability can be reduced possibly inducing her supersedure. She may also become the major cause of spreading the disease within the colony. On the other hand, beekeepers are naturally reluctant to destroy queens in the uncertain possibility that they are infected. The microscopic inspection of her faeces makes it possible to verify the presence or absence of the disease in the queen. Placed alone in a Petri dish, the queen will defecate in about an hour, the faeces appearing as colourless drops of clear liquid. This liquid can be examined under the microscope for the presence of spores, without further preparation (see OIE Manual of Diagnostics, 2004).

Control:

Nosema can best be controlled by keeping colonies as strong as possible and removing possible causes of stress. Colonies and apiaries should receive adequate ventilation and protection from the cold and from humidity. The bees should have the possibility of foraging regularly in order to defecate. This prevents spreading of the spores within the colony. Beekeepers should also ensure that their colonies and queens come from disease-free stock. Hive equipment that is suspected of being contaminated by Nosemaapis spores should be thoroughly decontaminated, preferably by heat and fumigation. The best prevention is to change the combs once every two years. During normal wax processing the Nosema spores are killed.

Parasitic Bee Mites

Varroa Mite (Varroasis)

The overall effect of varroa infestation is to weaken the honey bee colonies and thus decrease honey production, often seriously. Occasionally in A. melllfera heavy infestation may cause absconding. Today this parasite is found throughout the world, except for Australia and New Zealand South Island.

Cause:

Varroa destructor (previously confused with Varroajacobsonii) is quite large, as compared with other mite species, and can be seen with the unaided eye. The shape of the adult female is distinctive: observed from above, the width of the body is clearly seen to be greater than the length, i.e. about 1.6 x 1.1 mm. The mite is reddish brown in colour and shiny and the body is dorsoventrally flattened covered with short hairs (setae). Adult females of V. destructor are found inside brood cells or walking rapidly on comb surfaces. Individual mites are often seen clinging tightly to the body of adult bees, mostly on the abdomen, where the segments overlap, between the thorax and the abdomen and at the ventral entry. Adult males, and the immature stages of both sexes (egg, protonymph and deuteronymph), are not commonly seen outside the brood cells. All immature stages of the parasite live inside the brood cells. They can be observed when infested cells are opened and the brood is carefully removed. The immature mites are bright white and the adult females are brown, while male mites are smaller than females and are rarely seen since they are only found inside brood cells.

Symptoms:

Varroa causes injuries to honey bees by direct feeding. The adult female pierces the bees’ soft intersegmental membrane with their pointed chelicera and sucks the bees` haemolymph (‘blood’). The adult bee, however, is only damaged if the infestation is severe. Varroasis is a brood disease. If more than one parasitic female mite infests the brood cell the brood decays or deformations occur including shortened abdomen or deformed wings. If only one mite infests a cell symptoms may not be visible, although the bees’ life-span is considerably shortened. Moreover, the bee’s behaviour may be disturbed, e.g. in orientation or gathering food. Infested bees often have a reduced fat body that hampers the functioning of their glands or increases their susceptibility to pesticides. The semen production of drones may be considerably reduced. Varroasis is a multi-factorial disease. Virus diseases that may have caused little damage before infestation by varroa mites often accompany it. Normally, the exoskeleton protects the bees from many virus infections. However, the mite penetrates this natural barrier transferring viruses or stimulating the multiplication of viruses with its saliva. In turn viruses seem to speed the development of varroasis enhancing the parasite’s virulence. Other diseases such as nosema and sacbrood have similar effects. Moreover, unfavourable climatic conditions or insufficient stocks of pollen and nectar can increase the process of disintegration. Without treatment the colonies normally die after two to three years, management errors may also cause the collapse of colonies. Colonies destroyed by the varroa mite are often left with only a handful of bees and the queen, the other bees having died during foraging or having drifted to neighbouring colonies, where the mite population can increase before killing these colonies also. In this way mites may cause colonies to die, as in some kind of domino effect, over wide areas. The presence of adult bees with deformed wings, crawling on comb surfaces or near the hive entrance, usually indicates a late stage of heavy mite infestation. Several other methods may be used to detect mites. The most reliable, perhaps the most time-consuming, is direct sampling by the random opening of brood cells, particularly drone cells. The older the larvae/pupae the easier this procedure becomes. The brood is removed from the cell with a fine forceps and the cell is inspected for the presence of the mites. Between 100 and 200 cells must be opened before an assessment of the level of mite infestation can be made. To inspect adult bees, the bees are captured from the brood combs and placed in jars, into which chloroform, ether or alcohol is introduced on a piece of cotton wool. The bees are intoxicated and the mites crawl on the glass wall. Returning foragers may also be captured by hand at the hive entrance and held up against the sunlight; any mites attached to the bees’ abdomens may be seen. Another method is to use specially constructed zinc, plastic or wood trays, built to the size of the bottom board, with a white or light-coloured floor. The trays, equipped with a screen of a mesh less than 2 mm fixed at about 1 cm above the tray floor, are placed on the bottom boards of the hives and are inspected one to three days later for the presence of dead mites. The screen prevents the bees from removing the dead parasites from the hive (see OIE Manual of Diagnostics, 2004). The control of V. destructor is one of the most difficult tasks facing apiculturists and beekeepers throughout the world. The mite is a highly successful parasite, whose life history is well synchronized with that of its host. Two principal approaches to its control are currently available: chemical control and hive manipulation techniques, sometimes referred to as ‘biological control’. Chemical control creates the risk of honey contamination, the accumulation of residues within the hive and toxic effects to the bees, therefore we will focus on organic methods. If the application of chemical substances can not be avoided, it should only be started after honey harvest, i.e. after extraction of the honey chamber, respectively the honey combs. This is the only way to avoid residues.

Organic acids:

Most organic acids are natural components of honey. In most countries, no fixed maximum residue limits have been fixed for them. Obviously, overdosing can ‘over acid’ the honey and change its taste. Overdosing should also be avoided to avoid damage to the bees. Those handling acid must be aware of the risks and wear protective clothing. Formic acid is the strongest organic acid and can cause extremely severe skin burns if it comes in contact with the skin. Skin and eyes must be sufficient protected while the acid is being prepared and during its application. In addition, a bucket of water should be kept close by to serve as a ‘fire extinguisher’. Having to search for water when acid is already on the clothing or the skin may result in deep wounds. The same is true for oxalic acid. Here special precaution is necessary when preparing the solution with the crystal form. To avoid inhalation, a special mouth protector must be worn.

Formic acid:

Formic acid can kill some of the mites in the sealed brood cells. It is recommended that the formic acid be allowed to evaporate in colonies with sealed brood for at least two to three weeks. In this way, mites emerging from the brood will also be killed. Various applicators have proved effective for this purpose. A small container equipped with a wick or paper felt is filled with 200 ml of 85 percent formic acid to evaporate for at least 14 days. The quantity to evaporate can be regulated by means of the length of the wick or the size of the paper felt. The container is either placed on top of the combs, in an empty upper section or after some combs have been taken out, in the empty space. The external temperature should not be less than 12°C (54°F) and not more than 25°C (77°F). The formic acid should be introduced into the colony only in the late afternoon to avoid damage to bees and brood. In addition, physiological tolerance is improved if the entrance hole is wide open. An easier way to introduce formic acid is to use a sponge or a similarly absorbent material. A solution of 3 ml of 60 percent formic acid is applied onto the sponge tissue per comb (Langstroh size). The quantity must be reduced accordingly for smaller comb sizes. A grid fixed above the tissues on the bottom of the hive, will prevent the bees from burning themselves with the acid. The grid should be as far away from the brood as possible. The application can be repeated three to four times at intervals of at least seven days.

Oxalic acid:

Contrary to formic acid oxalic acid does not act via evaporation but through contact with the bees. Thirty five grams of crystal oxalic acid (dihydrate) is thinned in one litre of sugar water (1:1). When handling crystal acid special precautions must be taken because of the health risks. Protective spectacles and acid-proof gloves must be work together with an adequate mouth protector. Depending on the size of the colony 20 to 30 ml of the suspension per chamber are dropped into the bee-ways. A repetition of the treatment can lead to damage to the bees. Applicators are available by which the acid can be evaporated.

Lactic acid:

Lactic acid is clearly better tolerated by bees and does not cause problems in warmer climatic zones. The disadvantage is that every single comb must be extracted to spray the bees with the acid. The dosage applied per comb side is 8 ml of 15 percent acid. This treatment can be repeated several times at intervals of seven days
Etheric oilsThe only etheric oil that is sufficiently affective against varroa mites is thymol.
Thymol can be applied as a commercially available ready-made preparation or in crystal form. For this purpose, 0.5 mg thymol per bee-way are put into a gauze bag and deposited onto the combs for some weeks. In this way mites emerging from the brood will be covered.

Control by hive manipulation:

The varroa mite depends on bee brood to complete its development cycle. Since the mite prefers drone brood to worker brood, empty frames are given to the colonies, which will rear drone brood in them. When the cells are sealed, the frames, containing the mites trapped inside the cells, can be removed and destroyed. The mites can also be trapped in worker-brood frames by using vertical queen-excluders in singlestorey hives. The queen is confined between two excluders and allowed to lay eggs in one frame only. Female mites in the colony will be attracted to this brood frame which, when the cells are sealed, is removed from the colony so that the brood cells infested by the parasites can be destroyed.

Sources: FAO

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