Science Fair Project Encyclopedia
Diseases of the honeybee
Common diseases, parasites, pests, and ailments of the honeybee include:
- Varroa mite
- Acarine mites, formerly known as Tracheal mites
- American foulbrood (AFB)
- European foulbrood (EFB)
- Small hive beetle
- Wax moths
- Chilled brood
- Kashmir Bee Virus (KBV)
- Black Queen-Cell Virus (BQCV) (often concommitant with Nosema)
- Pesticide losses
Varroa destructor and Varroa jacobsoni are parasitic mites that feed off the bodily fluids of adult, pupal and larval bees. Varroa mites can be seen with the naked eye as a small red or brown spot on the bee's thorax. Varroa is a carrier for a virus that is particularly damaging to the bees. Bees that are infected with this virus during their development will often have a visible "K-wing" deformity. Varroa has led to the virtual elimination of feral bee colonies in many areas and is a major problem for kept bees in apiaries. Some feral populations are now recovering — it appears that they have been naturally selected for varroa resistance. Langstroth hives are believed by some (particularly top bar hive keepers) to be particularly favorable to varroa development.
Varroa is generally not a problem for a hive that is growing strongly. When the hive population growth reduced in preparation for winter or due to poor late summer forage the mite population growth can overtake that of the bees and can then destroy the hive. Often a colony will simply abscond (leave as in a swarm, but leaving no population behind) under such conditions.
Varroa mites can be treated with commercially-available miticides . Miticides must be applied strictly according to the label in order to minimize the risk of contamination of honey that might be consumed by humans. Proper use of miticides will also help to slow the development of resistance among the mites.
Varroa mites can also be controlled through non-chemical means. Most of these controls are intended to reduce the mite population to a manageable level, not to eliminate the mites completely.
- Many beekeepers use a screened bottom board on their hives. When mites occasionally fall off a bee, they must climb back up to parasitize a new bee. If the beehive has a screened floor with mesh the right size, the mite will fall through and can not return to the beehive. The screened bottom board is also being credited with increased circulation of air which reduces condensation in a hive during the winter.
- Powdered sugar, talc or other "safe" powders can be sprinkled on the bees. The powder does not harm the bees (and, if you use sugar, can even become a small source of feed), but does cause some of the mites to dislodge. Powdered sugar works best as an amplifier of the effects of a screened bottom board.
- Freezing drone brood takes advantage of varroa mites' preference for larger drone brood. The beekeeper will put a frame in the hive that is sized to encourage the queen to lay primarily drone brood. Once the brood is capped, the beekeeper removes the frame and puts it in the freezer. This kills the varroa mites that are parasitizing those bees. It also kills the drone brood, but most hives produce an excess of drone bees so it is not generally considered a loss. After freezing, the frame can be returned to the hive. The nurse bees will clean out the dead brood (and dead mites) and the cycle continues.
- Drone brood excision is applicable to top bar hives, as comb suitable for drone brood will usually be placed low and on the outer margins of the comb. Cutting this off at a late stage of development ("purple eye stage") allows for inspection and counting of varroa on the brood. It is generally considered acceptable if the number of varroa mites does not exceed 25 percent of the number of drone larvae and pupae. Note that miticides cannot be used in top bar hives due to the way comb is cycled through the hive for control of other diseases such as foul brood.
Several attempts have been made (and are continuing) to breed bees with an increased resistance to varroa mites. In fact, the Africanized honeybee was originally an experiment to cross-breed mite resistance into the European honeybees common in the Americas.
Acarine mites (Tracheal mites)
Acarapis woodi is a small parasitic mite that infests the airways of the honeybee. The first known infestation of the mites occurred in the British Isles in the early 20th century. First observed on the Isle of Wight in 1904, the mystery illness known as Isle of Wight Disease was not identified as caused by a parasite until 1921. It quickly spread to the rest of Great Britain. It was regarded as having wiped out the entire bee population of the isles (later genetic studies have found remnants that did survive) and dealt a devastating blow to British beekeeping. Brother Adam at the Buckfast Abbey developed a resistant hybrid bee known as the Buckfast bee, which is now available worldwide to combat acarine disease.
Acarine mites, formerly known as tracheal mites are believed to have entered the US in 1984 via Mexico.
Mature female acarine mites leave the bee's airway and climb out on a hair of the bee where they wait until they can transfer to a young bee. Once on the new bee, they will move into the airways and begin laying eggs.
Acarine mites are commonly controlled with grease patties (typically made from 1 part vegetable shortening mixed with 3-4 parts powdered sugar) placed on the top bars of the hive. The bees come to eat the sugar and pick up traces of shortening which disrupts the mite's ability to identify a young bee. Some of the mites waiting to transfer to a new host will remain on the original host. Others will transfer to a random bee - a proportion of which will die of other causes before the mite can reproduce.
Menthol, either allowed to vaporize from crystal form or mixed into the grease patties, is also often used to treat acarine mites.
Paenibacillus larvae (formerly classified as Bacillus larvae) is a spore-forming bacterium. This disease only affects the bee larvae but is highly infectious and deadly to bees. Infected larvae will darken and die. Lab testing is necessary for definitive diagnosis, but a good field test is to touch a dead larva with a toothpick or twig. It will will be sticky and ropey (draw out). Brood also has a characteristic odor, and experienced beekeepers with good smellers can often detect the disease upon opening a hive. In the photo at right, some larvae are healthy while others are diseased. Capped cells with decomposing larvae are sunken, as can be seen at lower right. Some caps may be torn as well. Compare with healthy brood.
Chemical treatment of American foulbrood is possible using oxytetracycline hydrochloride, but because of the persistence of the spores (which can survive up to 40 years), the most common treatment is the destruction of the colony and burning of all equipment.
Chemical treatment is sometimes used prophylactically, but this is a source of considerable controversy because the bacterium seems to be rapidly developing resistance.
Melissococcus pluton is a bacterial brood disease that infests the guts of bee larvae. European foulbrood is less deadly than American foulbrood. European foulbrood does not form spores, though it can overwinter on comb.
European foulbrood is often considered a "stress" disease - a disease that is dangerous only if the colony is already under stress for other reasons. An otherwise healthy colony can usually survive European foulbrood. The disease may be treated chemically with oxytetracycline hydrochloride.
Ascophaera apis is a fungal disease infests the gut of the larva. The fungus will compete with the larva for food, ultimately causing it to starve. The fungus will then go on to consume the rest of the larva's body, causing it to appear white and 'chalky'.
Chalkbrood is often considered another "stress" disease because the fungal spores are always present but are manageable by an otherwise healthy colony. Chalkbrood is most commonly visible during wet springs. Hives with Chalkbrood can generally be recovered by increasing the ventilation through the hive and/or by requeening the hive.
Nosema apis is a spore-forming parasite that invades the intestinal tracts of adult bees and causes nosema disease. Nosema is also associated with Black queen-cell virus. Nosema is normally only a problem when the bees can not leave the hive to eliminate waste (for example, during an extended cold spell in winter or when the hives are enclosed in a wintering barn). When the bees are unable to void (cleansing flights ), they can develop dysentery.
Nosema is treated by increasing the ventilation through the hive. Some beekeepers will treat a hive with antibiotics.
Nosema can also be prevented or minimized by removing much of the honey from the beehive then feeding the bees on sugar water in the late fall. Sugar water made from refined sugar has lower ash content than flower nectar, reducing the risk of dysentery, and may have essentially the same nutritional content, although this remains a point of controversy among some beekeepers.
Small hive beetle
Aethina tumida is a small, dark-colored beetle that lives in beehives.
Originally from Africa, the first discovery of small hive beetles in the US occurred in Florida in 1987.
The life cycle of this beetle includes part of its development in the ground outside of the hive. Controls to prevent ants from climbing into the hive are believed to also be effective against the hive beetle.
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See main article Wax moth
Galleria mellonella (greater wax moths) will not attack the bees directly, but feed on the wax used by the bees to build their honeycomb. Their full development to adults requires access to used brood comb or brood cell cleanings — these contain protein essential for the larvae's development. The destruction of the comb will spill or contaminate stored honey and may kill bee larvae.
When honey supers are stored for the winter the wax moth larvae can destroy portions of the comb, even though they will not fully develop. Damage comb may be scraped out and will be replaced by the bees.
A strong hive generally needs no treatment to control wax moths. The bees themselves will kill and clean out the moth larvae and webs. Wax moth larvae may fully develop in cell cleanings when such cleanings accumulate thickly where they are not accessible to the bees.
Wax moth development in comb is generally not a problem with top bar hives as unused combs are usually left in the hive during the winter. Since this type of hive is not used in severe wintering conditions, the bees will be able to patrol and inspect the unused comb.
Wax moths can be controlled chemically (the equivalent of moth balls) or by freezing the comb. If chemical methods are used the combs must be well aired out for several weeks before use.
Because wax moths can not survive a cold winter, they are usually not a problem for beekeepers in the northern U.S. or Canada.
Chilled brood is not actually a disease but can be a result of mistreatment of the bees by the beekeeper. It also can be caused by a pesticide hit that primarily kills off the adult population, or by a sudden drop in temperature during rapid spring buildup. Brood must be kept warm at all times. Nurse bees cluster over the brood to keep it at the right temperature. When a beekeeper opens the hive (to inspect, remove honey, check the queen, or just because he/she is curious) and prevents the nurse bees from clustering on the frame for too long, the brood can become chilled, deforming or even killing some of the bees.
To minimize the risk of chilled brood, open the hive on warm days and at the hottest part of the day. (This is also the time when the most field bees will be out foraging and the number of bees in the hive will be at its lowest.) Learn to inspect your hive as quickly as possible and put frames with brood back where the bees can cluster on it immediately.
Kashmir Bee Virus
Black Queen-Cell Virus
Honeybees are susceptible to many of the chemicals used for agricultural spraying of other insects and pests. Many pesticides are known to be toxic to bees. Because the bees forage up to several miles from the hive, they may fly into areas actively being sprayed by farmers or they may collect pollen from 'contaminated' flowers.
Pesticide losses may be relatively easy to identify (large and sudden numbers of dead bees in front of the hive) or quite difficult, especially if the loss results from a gradual accumulation of pesticide brought in by the foraging bees. Quick acting pesticides may deprive the hive of its foragers, dropping them in the field before they can return home.
Insecticides that are toxic to bees have label directions that protect the bees from poisoning as they forage. To comply with the label, applicators must know where and when bees forage in the application area, and the length of residual activity of the pesticide.
Some pesticide authorities recommend, and some jurisdictions require, that notice of spraying be sent to all known beekeepers in the area so that they can seal the entrances to their hives and keep the bees inside until the pesticide has had a chance to disperse. However, sealing honeybees from flight on hot days can also kill bees. Beekeeper notification does not comply with the label directions, nor does it offer any protection to bees, if the beekeeper cannot access them, nor to wild native bees or feral honeybees. Thus beekeeper notification as a normal procedure does not really protect all the pollinators of the area, and is, in effect, a circumventing of the label requirements. Pesticide losses are a major factor in pollinator decline.
External links and references
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