Varroa destructor

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Varroa mite
Varroa Mite.jpg
Scientific classification
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V. destructor
Binomial name
Varroa destructor
Anderson & Trueman, 2000

Varroa destructor (Varroa mite) is an external parasitic mite that attacks and feeds on the honey bees Apis cerana and Apis mellifera . The disease caused by the mites is called varroosis.

Contents

The Varroa mite can reproduce only in a honey bee colony. It attaches to the body of the bee and weakens the bee by sucking fat bodies. [1] The species is a vector for at least five debilitating bee viruses, [1] including RNA viruses such as the deformed wing virus (DWV). A significant mite infestation leads to the death of a honey bee colony, usually in the late autumn through early spring. The Varroa mite is the parasite with possibly the most pronounced economic impact on the beekeeping industry. Varroa is considered to be one of multiple stress factors [2] contributing to the higher levels of bee losses around the world.

Physical description

The adult female mite is reddish-brown in color, while the male is white. Varroa mites are flat, having a button shape. They are 1–1.8 mm long and 1.5–2 mm wide, and have eight legs.

Reproduction, feeding, infection, and hive mortality

Mites reproduce on a 10-day cycle. The female mite enters a honey bee brood cell. As soon as the cell is capped, the Varroa mite lays eggs on the larva. The young mites, typically several females and one male, hatch in about the same time as the young bee develops and leave the cell with the host. When the young bee emerges from the cell after pupation, the Varroa mites also leave and spread to other bees and larvae. The mite preferentially infest drone cells, allowing the mite to reproduce one more time with the extra three days it takes a drone to emerge compared to a worker bee. This can cause genetic defects such as useless wings or viruses and fungi in the bee.

Adult mites suck on the fat body of both adult bees and bee larvae for sustenance. As the fat body is crucial for many bodily functions such as hormone and energy regulation, immunity, and pesticide detoxification, the bee is left in a severely weakened state. Adult mites live and feed under the abdominal plates of adult bees primarily on the underside of the metasoma region on the left side of the bee. Adult mites are more often identified as present in the hive when on top of the adult bee on the mesosoma region, but research suggests that mites in this location are not feeding, but rather attempting to transfer to another bee. [1]

Preferred feeding location of V. destructor mites on adult host bees, figure 1 from Varroa destructor feeds primarily on honey bee fat body tissue and not hemolymph Preferred feeding location of Varroa destructor mites on adult host bees.jpg
Preferred feeding location of V. destructor mites on adult host bees, figure 1 from Varroa destructor feeds primarily on honey bee fat body tissue and not hemolymph

Open wounds left by the feeding become sites for disease and virus infections. The mites are vectors for at least five and possibly up to 18 debilitating bee viruses, [1] including RNA viruses such as the deformed wing virus. With the exception of some resistance in the Russian strains and bees that have Varroa-sensitive hygiene (about 10% of colonies naturally have it), European Apis mellifera bees are almost completely defenseless against these parasites. (Russian honey bees are one-third to one-half less susceptible to mite reproduction). [3]

The model for the population dynamics is exponential growth when bee broods are available, and exponential decline when no brood is available. In 12 weeks, the number of mites in a western honey bee hive can multiply by (roughly) 12. High mite populations in the autumn can cause a crisis when drone rearing ceases and the mites switch to worker larvae, causing a quick population crash and often hive death.

Low-temperature scanning electron micrograph of V. destructor on a honey bee host Varroa destructor on honeybee host.jpg
Low-temperature scanning electron micrograph of V. destructor on a honey bee host

Once infected with a V. destructor mite, the honey bee may be damaged two ways. Firstly, the mite's consumption of the fat body weakens both the adult bee and the larva; in particular, it significantly decreases the weight of both the hatching and adult bee. Additionally, infected adult worker bees have a shorter lifespan than ordinary worker bees, and they furthermore tend to be absent from the colony far more than ordinary bees, which could be due to their reduced ability to navigate or regulate their energy for flight. Secondly, the mites are vectors of various viruses, in particular the deformed wing virus. [4]

After the initial developmental stages, when the young bee matures, it leaves the brood cell and takes the mite with it. V. destructor then leaves the young bee for an older one, preferably for a nurse bee, because nurse bees spend more time near the brood, giving the mite more ample opportunity to reproduce. In fact, because the nurse bee spends more time around the drone brood rather than the worker brood, many more drones are infected with the mites. [4]

Varroa mites have been found on tricial larvae of some wasp species, such as Vespula vulgaris , and flower-feeding insects such as the bumblebee, Bombus pennsylvanicus , the scarab beetle, Phanaeus vindex , and the flower-fly, Palpada vinetorum. [5] It parasitizes the young larvae and feeds on the internal organs of the hosts. Although the Varroa mite cannot reproduce on these insects, its presence on them may be a means by which it spreads short distances (phoresy).

Varroa mites on pupa Vorroa Mite on pupa.JPG
Varroa mites on pupa
Varroa mites on pupae Drohnenpuppen mit Varroamilben 71a.jpg
Varroa mites on pupae
Varroa destructor on bee larva Varroa on larvae.jpg
Varroa destructor on bee larva

Introduction around the world

Varroa mites originally only occurred in Asia, on the Asian honeybee, Apis cerana , but this species has been introduced to many other countries on several continents, resulting in disastrous infestations of European honeybees. [6]

As of mid-2012, Australia is thought to be free of the mite. [14] [15] In early 2010, an isolated subspecies of bee was discovered in Kufra (southeastern Libya) that appears to be free of the mite. [16] The Hawaiian islands of Maui, Kauai, Molokai, and Lanai are all free of the mite.

Identification

Until recently, V. destructor was thought to be a closely related mite species called Varroa jacobsoni . Both species parasitize the Asian honey bee, A. cerana. However, the species originally described as V. jacobsoni by Anthonie Cornelis Oudemans in 1904 is not the same species that also attacks A. mellifera. The jump to A. mellifera probably first took place in the Philippines in the early 1960s, where imported A. mellifera came into close contact with infected A. cerana. Until 2000, scientists had not identified V. destructor as a separate species. This late identification in 2000 by Anderson and Trueman corrected some previous confusion and mislabeling in the scientific literature. [17]

Varroosis

The infestation and subsequent parasitic disease caused by Varroa mites is called varroosis. Sometimes, the incorrect names varroatosis or varroasis are used. A parasitic disease name must be formed from the taxonomic name of the parasite and the suffix -osis [18] as provided in the Standardised Nomenclature by the World Association for the Advancement of Veterinary Parasitology. [19] For example, the World Organisation for Animal Health (OIE) uses the name varroosis in the OIE Terrestrial Manual. [20]

Treatments have met with limited success. First, the bees were medicated with fluvalinate, a synthetic pyrethroid, which had about 95% mite falls. However, the last 5% became resistant to it, and later, almost immune. Fluvalinate was followed by coumaphos.

Control or preventive measures and treatment

Honeybee coated with oxalic acid to protect it from mites Beecrystals.PNG
Honeybee coated with oxalic acid to protect it from mites

Monitoring

Several methods exist for monitoring levels of Varroa mites in a colony. [21] For a powdered sugar roll, [22] the sampler collects about 300 bees using a 1/2-cup measuring cup and places them in a jar with a wire mesh screen lid (1/8") along with 2 tablespoons of powdered sugar. They then gently swirl the bees for about a minute before turning the jar upside down and shaking for two minutes over a tray to capture the mites as they fall. Those mites are then counted, and the count is divided by three to find the number of mites per 100 bees. The sugar roll is typically done with the intent to prevent killing the sampled bees, but whether the vigorous shaking causes damage is not known. For an alcohol wash, which is the most effective method, the sampler collects about 300 bees using the same cup. The bees are submerged in alcohol with a concentration of 70% or higher. A lid is placed over the jar to seal it, and the mixture is shaken vigorously for two minutes before it is poured over a 1/8" wire mesh screen into a tray. The mites are then counted, and the resulting number is also divided by three. This method kills all sampled bees. The sticky board method does not kill any bees. For this method, a sticky board with a thick coating of petroleum jelly is placed under the brood chamber under a screened bottom board (or similar 1/8" wire mesh screen). The board is retrieved after three days, and the beekeeper takes a count of the mites on the board. This number is divided by three to find the average 24-hour mite drop. This method does not kill any bees, but takes longer for results.

Chemical measures

Varroa mites can be treated with commercially available acaricides.[ citation needed ] Acaricides must be applied carefully to minimize the contamination of honey that might be consumed by humans. Proper use of miticides also slows the development of resistance by the mites.

Synthetic chemicals

Naturally occurring chemicals

  • Formic acid as vapor or pads (Mite-Away)
  • Powdered sugar (Dowda method), talc, or other "safe" powders with a grain size between 5 and 15 μm (0.20 and 0.59 mils) can be sprinkled on the bees.
  • Essential oils, especially lemon, mint, and thyme oil [24]
  • Sugar esters (Sucrocide) in spray application
  • Oxalic acid trickling method or applied as vapor
  • Mineral oil (food grade) as vapor and in direct application on paper or cords
  • Natural hops compounds in strip application (Hopguard)

However, the most effective long-term way of protecting bees against V. destructor is by breeding bees that are resistant to these mites. [4]

Physical, mechanical, behavioral methods

Varroa mites can also be controlled through nonchemical means. Most of these controls are intended to reduce the mite population to a manageable level, not to eliminate the mites completely.

Genetic engineering

Researchers have been able to use RNA interference to knock out genes in the Varroa mite. Efforts also have been made to breed for changes in the honey bees. [29] Two strains have been developed in the United States that can detect damaged pupae under cappings and remove them before the infestation spreads further. [30] [31] The “IN”/Indiana strain is under development at Purdue University to develop lines that groom off and bite phoretic Varroa to kill the mites. [32] [33]

See also

Related Research Articles

Honey bee Eusocial flying insect of genus Apis, producing surplus honey

A honey bee is a eusocial flying insect within the genus Apis of the bee clade, all native to Eurasia but spread to four other continents by human beings. They are known for construction of perennial, colonial nests from wax, for the large size of their colonies, and for their surplus production and storage of honey, distinguishing their hives as a prized foraging target of many animals, including honey badgers, bears and human hunter-gatherers. Only seven surviving species of honey bee are recognized, with a total of 44 subspecies, though historically seven to eleven species are recognized. Honey bees represent only a small fraction of the roughly 20,000 known species of bees.

Beekeeping care and breeding of honey bees

Beekeeping is the maintenance of bee colonies, commonly in man-made hives, by humans. Most such bees are honey bees in the genus Apis, but other honey-producing bees such as Melipona stingless bees are also kept. A beekeeper keeps bees in order to collect their honey and other products that the hive produce, to pollinate crops, or to produce bees for sale to other beekeepers. A location where bees are kept is called an apiary or "bee yard".

Bee brood

In beekeeping, bee brood or brood refers to the eggs, larvae and pupae of honeybees. The brood of Western honey bees develops within a bee hive. In man-made, removable frame hives, such as Langstroth hives, each frame which is mainly occupied by brood is called a brood frame. Brood frames usually have some pollen and nectar or honey in the upper corners of the frame. The rest of the brood frame cells may be empty or occupied by brood in various developmental stages. During the brood raising season, the bees may reuse the cells from which brood has emerged for additional brood or convert it to honey or pollen storage. Bees show remarkable flexibility in adapting cells to a use best suited for the hive's survival.

European dark bee subspecies of the western honey bee

The European dark bee is a subspecies of the western honey bee, whose original range stretched from west-central Russia through Northern Europe and probably down to the Iberian Peninsula. They belong to the 'M' lineage of Apis mellifera. They are large for honey bees though they have unusually short tongues (5.7-6.4 mm) and traditionally were called the German Dark Bee or the Black German Bee, names still used today even though they are now considered an Endangered Breed in Germany. Their common name is derived from their brown-black color, with only a few lighter yellow spots on the abdomen. However today they are more likely to be called after the geographic / political region in which they live such as the British Black Bee, the Native Irish Honey Bee, the Cornish Black Bee and the Nordic Brown Bee, even though they are all the same subspecies, with the word “native” often inserted by local beekeepers, even in places where the bee is an introduced foreign species. It was domesticated in Europe and hives were brought to North America in the colonial era in 1622 where they were referred to as the English Fly by the Native American Indians.

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Russian honey bee honey bees that originate in the Primorsky Krai region of Russia

The Russian honeybee refers to honey bees that originate in the Primorsky Krai region of Russia. This strain of bee was imported into the United States in 1997 by the USDA's Honeybee Breeding, Genetics & Physiology Laboratory in Baton Rouge, Louisiana in response to severe declines in bee populations caused by infestations of parasitic mites, and has been used in breeding programs to improve existing stocks. Many Russian queens openly mate with drones from various stock, creating colonies that are genetically hybrid. Some of these 'uncontrolled' hybrids may exhibit "increased aggressiveness, reduced honey production and a decrease in their ability to withstand mites and detrimental expressions of other traits as well."

<i>Varroa</i> genus of arthropods

Varroa is a genus of parasitic mites associated with honey bees, placed in its own family, Varroidae. The genus was named for Marcus Terentius Varro, a Roman scholar and beekeeper. The condition of a honeybee colony being infested with Varroa mites is called varroosis.

<i>Varroa jacobsoni</i> species of arthropods

Varroa jacobsoni is a species of mite that parasitises Apis cerana. The more damaging Varroa destructor was previously included under the name V. jacobsoni, but the two species can be separated on the basis of the DNA sequence of the cytochrome oxidase I gene in the mitochondrial DNA.

<i>Apis koschevnikovi</i> species of insect

Apis koschevnikovi, Koschevnikov's honey bee, is a species of honey bee which inhabits Malaysian and Indonesian Borneo, where it lives sympatrically with other honey bee species such as Apis cerana.

<i>Apis dorsata</i> species of insect

Apis dorsata, the giant honey bee, is a honey bee of South and Southeast Asia, found mainly in forested areas such as the Terai of Nepal. They are typically around 17–20 mm (0.7–0.8 in) long. Nests are mainly built in exposed places far off the ground, like on tree limbs, under cliff overhangs, and sometimes on buildings. These social bees are known for their aggressive defense strategies and vicious behavior when disturbed. Though not domesticating it, indigenous peoples have traditionally used this species as a source of honey and beeswax, a practice known as honey hunting.

<i>Deformed wing virus</i> species of virus

Deformed wing virus (DWV) is an RNA virus, one of 22 known viruses affecting honey bees. While most commonly infecting the honey bee, Apis mellifera, it has also been documented in other bee species, like Bombus terrestris, thus, indicating it may have a wider host specificity than previously anticipated. The virus was first isolated from a sample of symptomatic honeybees from Japan in the early 1980s and is currently distributed worldwide. It is found also in pollen baskets and commercially reared bumblebees. Its main vector in A. mellifera is the Varroa mite. It is named after what is usually the most obvious deformity it induces in the development of a honeybee pupa, which is shrunken and deformed wings, but other developmental deformities are often present.

Western honey bee Species of insect

The western honey bee or European honey bee is the most common of the 7–12 species of honey bees worldwide. The genus name Apis is Latin for "bee", and mellifera is the Latin for "honey-bearing", referring to the species' production of honey.

Colony collapse disorder Poorly-understood phenomenon causing decline in bee populations


Colony collapse disorder (CCD) is an abnormal phenomenon that occurs when the majority of worker bees in a honey bee colony disappear, leaving behind a queen, plenty of food, and a few nurse bees to care for the remaining immature bees. While such disappearances have occurred sporadically throughout the history of apiculture, and have been known by various names, the syndrome was renamed colony collapse disorder in late 2006 in conjunction with a drastic rise in reports of disappearances of western honey bee colonies in North America. Beekeepers in most European countries have observed a similar phenomenon since 1998, especially in Southern and Western Europe; the Northern Ireland Assembly received reports of a decline greater than 50%. The phenomenon became more global when it affected some Asian and African countries as well.

<i>Apis cerana</i> species of insect

Apis cerana, the eastern honey bee, Asiatic honey bee or Asian honey bee, is a species of honey bee native to southern, southeastern, and eastern Asia. This species is the sister species of Apis koschevnikovi and both are in the same subgenus as the western (European) honey bee, Apis mellifera. A. cerana is known to live sympatrically along with Apis koschevnikovi within the same geographic location. Apis cerana colonies are known for building nests consisting of multiple combs in cavities containing a small entrance, presumably for defense against invasion by individuals of another nest. The diet of this honey bee species consists mostly of pollen and nectar, or honey. Moreover, Apis cerana is known for its highly social behavior, reflective of its classification as a type of honey bee.

Varroa sensitive hygiene (VSH) is a behavioral trait of honey bees (Apis mellifera) in which bees detect and remove bee pupae that are infested by the parasitic mite Varroa destructor. V. destructor is considered to be the most dangerous pest problem for honey bees worldwide. VSH activity results in significant resistance to the mites.

Beekeeping in Ireland has been practiced for at least 2000 years and has seen a surge in popularity in modern times, evidenced by the numerous organizations promoting and assisting beekeeping. Despite the increased pressures on bees and beekeepers through new diseases and loss of habitat, there are now in excess of 3,500 members within beekeeping associations.

Chronic bee paralysis virus (CBPV) commonly affects adult Apis mellifera honey bees and causes a chronic paralysis that can easily spread to other members of a colony. Bees infected with CBPV begin to show symptoms after 5 days and die a few days after. Chronic bee paralysis virus infection is a factor that can contribute to or cause the sudden collapse of honeybee colonies. Since honeybees serve comprise a vital force in ecological resilience, it is important to understand factors and diseases that threaten them.

<i>Slow bee paralysis virus</i> species of virus

Slow bee paralysis virus (SBPV) is a virus discovered in England in 1974 that infects honeybees, bumblebees, and silkworms through Varroa destructor mite infestations. The virus causes paralysis in the front two pairs of legs of adult bees eventually killing its hosts. The virus is in the iflaviridae family of viruses. Infection by iflaviridae viruses is among the leading cause of death of honeybee colonies. As bees and silkworms are of great economic and biological importance, the virus is the subject of ongoing research.

Mite biting bees

Mite biting bees is a natural defensive behavior of honeybees to fight off the ectoparasitic mites Varroa destructor. This behavior has been studied for several decades for honeybee breeding and improve honeybee stocks on mite resistance. A group effort at Purdue University started an artificial selection of mite biting behavior of European Honeybees with Heartland Honey Bee Breeding Coop (HHBBC)

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Further reading