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Diseases of the honeybee

Common diseases and ailments of the honeybee include:
  • Varroa mites
  • Tracheal mites
  • American foulbrood (AFB)
  • European foulbrood (EFB)
  • Chalkbrood
  • Nosema
  • Small hive beetle
  • Wax moths
  • Chilled brood

Table of contents

Varroa mites Varroa destructor is a parasitic mite that feeds 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 were 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 and is a major problem for kept bees.

Varroa was first discovered in Southeast Asia in about 1904, but has now spread virtually worldwide. Varroa was discovered in the United States in 1987. see also Varroa Map (http://www.maf.govt.nz/biosecurity/pests-diseases/animals/varroa/maps/2000varroa-global-animap.htm)

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 managable level, not to eliminate the mites completely.

  • More and more 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 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.

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.

Tracheal mites Acarapis woodi is a small parasitic mite that infests the airways of the honeybee. Diagnosis for tracheal mites generally involves the dissection[?] of a sample of bees from the hive.

Tracheal mites are believed to have entered the US in 1984 via Mexico.

Tracheal mites are commonly controlled with Menthol, either allowed to vaporize from crystal form or by feeding the bees grease patties mixed with menthol.

American foulbrood 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. Dead larvae will will be sticky or ropey.

Chemical treatment of American foulbrood is possible using oxytetracycline hydrochloride, but because of the persistance 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.

European foulbrood Melissococcus pluton is a bacterial brood disease that infests the guts of bee larvae. European foulbrood is generally considered to be less deadly than American foulbrood. European foulbrood does not form spores, though it can overwinter on comb.

European foulbrood is generally treated chemically with oxytetracycline hydrochloride.

Chalkbrood Ascophaera apis is a fungal disease that causes infected bee larvae to appear white and 'chalky'.

Hives with Chalkbrood can generally be recovered by increasing the ventilation through the hive and/or by requeening the hive.

Nosema Nosema apis is caused by a spore-forming protozoan that invades the intestinal tracts of adult bees. 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).

Nosema is treated by increasing the ventilation through the hive. Some beekeepers will treat a hive with antibiotics.

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.

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Wax moths Galleria mellonella (wax moths) will not attack the bees directly, but feed on the wax used by the bees to build their honeycomb. The destruction of the comb, though, will spill or contaminate stored honey and may kill bee larvae.

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 moths are a significant challenge for beekeepers, though, because they can destroy the carefully built frames of empty comb that the beekeeper is saving for the next season.

Wax moths can be controlled chemically (the equivalent of moth balls) or by freezing the comb. 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 Chilled brood is not actually a disease but is usually a result of mistreatment of the bees by the beekeeper. 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.

Pesticide losses Honeybees are susceptible to many of the chemicals used for agricultural spraying of other insects and pests. 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.

Most 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.

See also: Africanized bee, bee

External links and references

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