Diseases of the honey bee or abnormal hive conditions include:
Pests and parasites
Varroa mites
Varroa destructor and V. jacobsoni are parasitic mites that feed on the fat bodies of adult, pupal and larval bees. When the hive is very heavily infested, Varroa mites can be seen with the naked eye as a small red or brown spot on the bee's thorax. Varroa mites are carriers for many viruses that are damaging to bees. For example, bees infected during their development will often have visibly deformed wings. Varroa mites have led to the virtual elimination of feral bee colonies in many areas, and are a major problem for kept bees in apiaries. Some feral populations are now recovering—it appears they have been naturally selected for Varroa resistance. Varroa mites were first discovered in Southeast Asia in about 1904, but are now present on all continents, following their introduction to Australia in 2022. They were discovered in the United States in 1987, in the United Kingdom in 1992, and in New Zealand in 2000. To the untrained eye, these mites are generally not a very noticeable problem for a strongly growing hive- as the bees may appear strong in number, and may even be very effective at foraging. However, the mite reproduction cycle occurs inside the capped pupae, and the mite population can surge as a result of colony growth. Careful observation of a colony can help identify signs of disease often spread by mites. When the hive population growth is 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. It has been observed diseased colonies may slowly die off and be unable to survive through winter even when adequate food stores are present. Often a colony will simply abscond (leave as in a swarm, but leaving no population behind) under such conditions. Varroa in combination with viral vectors and bacteria have been theoretically implicated in colony collapse disorder. It is known that thymol, a compound produced by thyme, naturally occurring in thyme honey, is a treatment for Varroa, though it may cause bee mortality at high concentrations. Provisioning active colonies with crops of thyme may provide the colony with a non-interventional chemical defense against Varroa.
Treatment A variety of chemical and mechanical treatments are used to attempt to control Varroa mites.
"Hard" chemicals
"Hard" chemical treatments include amitraz (marketed as "Apivar"), fluvalinate (marketed as "Apistan"), coumaphos (marketed as CheckMite), flumethrin (marketed as "Bayvarol" and "Polyvar Yellow").
"Soft" chemicals
"Soft" chemical treatments include thymol (marketed as "ApiLife-VAR" and "Apiguard"), sucrose octanoate esters (marketed as "Sucrocide"), oxalic acid (marked as "Api-bioxal") and formic acid (sold in liquid form or in gel strips as Mite Away Quick Strips and Formic Pro, but also used in other formulations). According to the U.S. Environmental Protection Agency, when used in beehives as directed, chemical treatments kill a large proportion of the mites while not substantially disrupting bee behavior or life span. Use of chemical controls is generally regulated and varies from country to country. With few exceptions, they are not intended for use during production of marketable honey.
"Mechanical" treatments
Common mechanical controls generally rely on disruption of some aspect of the mites' lifecycle. These controls are generally intended not to eliminate all mites, but merely to maintain the infestation at a level which the colony can tolerate. Examples of mechanical controls include drone brood sacrifice (Varroa mites are preferentially attracted to the drone brood), powdered sugar dusting (which encourages cleaning behavior and dislodges some mites), screened bottom boards (so any dislodged mites fall through the bottom and away from the colony), brood interruption and, perhaps, downsizing of the brood cell size.
Acarine (tracheal) mites Acarapis woodi is a parasitic mite that infests the trachea that lead from the first pair of thoracic spiracles. An unidentified bee illness was first reported on the Isle of Wight in England in 1904, becoming known as the 'Isle of Wight disease' (IoWD), which was initially thought to be caused by Acarapis woodi when it was identified in 1921 by Rennie. The IoWD disease quickly spread to the rest of Great Britain and Ireland, dealing a devastating blow to British and Irish beekeeping, being claimed as having wiped out the indigenous bee population of the British Isles. In 1991 Bailey and Ball stated "The final opinion of Rennie (1923), a co-discoverer of Acarapis woodi, who had much experience with bees said to have the Isle of Wight Disease, was that under the original and now quite properly discarded designation 'Isle of Wight Disease' were included several maladies having analogous superficial symptoms", the authors came to the firm conclusion that the IoWD was not caused by acarine (Acarapis woodi) mites solely, but primarily by chronic bee paralysis virus (CBPV), even though Acarapis woodi was always found to be present within the hive whenever CBPV symptoms were observed. Brother Adam at Buckfast Abbey developed a resistant bee breed known as the Buckfast bee, which is now available worldwide. Diagnosis for tracheal mites generally involves the dissection and microscopic examination of a sample of bees from the hive. Acarapis woodi are believed to have entered the U.S. in 1984, from 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 move into the airways and begin laying eggs.
Treatment Acarine mites are commonly controlled with grease patties (typically made from one part vegetable shortening mixed with three to four 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 remain on the original host. Others 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.
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