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Varroa destructor
Varroa destructor adult female in dorsal (top) and ventral (lower) views
Scientific classification Edit this classification
Kingdom: Animalia
Phylum: Arthropoda
Subphylum: Chelicerata
Class: Arachnida
Order: Mesostigmata
Family: Varroidae
Genus: Varroa
Species:
V. destructor
Binomial name
Varroa destructor
Anderson & Trueman, 2000[1]

Varroa destructor, the Varroa mite, is an external parasitic mite that attacks and feeds on honey bees and is one of the most damaging honey bee pests in the world.[2][3] A significant mite infestation leads to the death of a honey bee colony, usually in the late autumn through early spring. Without management for Varroa mite, honey bee colonies typically collapse within 2 to 3 years in temperate climates.[4] These mites can infest Apis mellifera, the western honey bee, and Apis cerana, the Asian honey bee. Since it is very similar physically to the closely related Varroa jacobsoni, these species were thought to be one prior to 2000, but they were found to be two separate species by DNA analysis.

Parasitism of bees by mites in the genus Varroa is called varroosis. The Varroa mite can reproduce only in a honey bee colony. It attaches to the body of the bee and weakens the bee.[5] The species is a vector for at least five debilitating bee viruses,[5] including RNA viruses such as the deformed wing virus (DWV). The Varroa mite is the parasite with possibly the most pronounced economic impact on the beekeeping industry and is one of multiple stress factors contributing to the higher levels of bee losses around the world.[6] Varroa mite has also been implicated as one of the multiple causes of colony collapse disorder.

Management of this pest focuses on reducing mite numbers through monitoring to avoid significant hive losses or death. 3% of bees infested in a hive is considered an economic threshold where damage is high enough to warrant additional management. Miticides are available, though some are difficult to time correctly while avoiding harm to the hive, and resistance has occurred for others. Screened bottom boards on hives can be used for both monitoring and mite removal, and drone comb, which mites prefer, can be used as a trap to remove mites from the hive. Honey bee lines in breeding programs also show partial resistance to Varroa mite through increased hygienic behavior that is being incorporated as an additional management strategy.

Description and taxonomy

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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.[7] Varroa mites lack eyes.[8] These mites have curved bodies that allow them to fit between the abdominal segments of adult bees.[9]

Host bee species can help differentiate mite species in the genus Varroa; both V. destructor and Varroa jacobsoni parasitize Apis cerana, the Asian honey bee, but the closely related mite species originally described as V. jacobsoni by Anthonie Cornelis Oudemans in 1904 does not attack Apis mellifera, the western honey bee, unlike V. destructor. Until 2000, V. destructor was thought to be V. jacobsoni and resulted in some mislabeling in the scientific literature.[1][10] The two species cannot be easily distinguished with physical traits and have 99.7% similar genomes,[11] so DNA analysis is required instead.[1][12] Because the more virulent and damaging species V. destructor could not be distinguished at the time, most pre-2000 research on western honey bees that refers to V. jacobsoni was actually research on V. destructor.[4]

Other Varroa species V. underwoodi and V. rindereri can also parasitize honey bee species and can be distinguished from V. destructor and V. jacobsoni with slight differences in body size and setae characteristics, though each of the four species within the Varroa genus have similar physical characteristics.[13][14] If a Varroa species is found on a western honey bee, it will typically be V. destructor except where V. underwoodi is present, such as in Papua New Guinea.[14]

The name "Varroa mite" is typically used as the common name for V. destructor after the species was considered separate from V. jacobsoni.[9]

Bee hosts of Varroa species[13]
Mite species Bee host
Varroa destructor western honey bee, Asian honey bee
Varroa jacobsoni Asian honey bee
Varroa rindereri Apis koschevnikovi
Varroa underwoodi western honey bee, Asian honey bee, Apis nigrocincta, Apis nuluensis

Varroa mite has two distinct genetic strains from when it switched hosts from the Asian honey bee to the western honey bee: Korean and Japanese. The Korean strain that emerged in 1952 is now found worldwide in high frequencies, while the Japanese strain that started around 1957 occurs in similar areas at much lower frequencies.[11] Varroa mite has low genetic diversity, which is typical for an invasive species undergoing a range or host expansion.[15]

Range

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Varroa mites originally occurred only in Asia on the Asian honey bee, but this species has been introduced to many other countries on several continents, resulting in disastrous infestations of European honey bees.[16]

Introduction data prior to 2000 is unclear because of confusion with V. jacobsoni. By 2020, V. destructor was confirmed to be present throughout North America (excluding Greenland), South America, most of Europe and Asia, and portions of Africa. The species was not present in Australia as well as Oman, Congo, Democratic Republic of Congo, and Malawi. It was suspected to not be present in Sudan and Somalia.[17][18] Mites were found in 2022 in New South Wales in Australia.[19]

Life cycle

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Female mites enter brood cells to lay eggs on the comb wall after the cell is capped. Eggs are approximately 0.2 to 0.3 mm in diameter and cannot be seen without magnification. These eggs hatch into male and female protonymphs that are both transparent white. Immature mites can only feed on capped brood, so the life cycle cannot be completed during broodless periods. Protonymphs molt into deuteronymphs that more closely resemble the curved body of adults before they molt into adults. Development time from egg to adult is 6–7 days. Males will not leave brood cells and only mate with females present in the brood cell.[9]

Adult females can be found feeding both on brood and adult bees. After reaching the adult stage, females will leave the brood cell and enter a phoretic stage where mites attach to adult bees in order to disperse. Mites will feed on adult bees at this time and can be transmitted from bee to bee during this stage. Nurse bees are preferred hosts in order to be moved to new brood cells. Because the nurse bee spends more time around the drone brood (i.e., male bees) rather than the worker brood, many more drones are infected with the mites.[4] These phoretic females can also be transmitted to other hives through bee contact or hive equipment transfer. The phoretic stage can last for 4.5–11 days during brood production periods or up to five to six months when no brood is present in winter months. Female mites have a life expectancy of 27 days when brood is present.[9]

After the phoretic stage, female mites leave the adult bee and enter brood cells with bee larvae. Drone cells are preferred over workers. These females are called foundress mites, and they bury themselves in brood food provided by worker bees before the cell is capped. Brood cell capping begins egg cell activation for a foundress mite while she emerges to feed on the larva.[11] She will lay a single unfertilized egg after feeding to produce a male mite. After laying this egg, fertilized eggs to produce females are laid approximately once a day. Both the mother and nymphs will feed on the developing pupa. Unless multiple foundress mites are present in a cell, mating occurs between siblings when they reach the adult stage. Once females mate, they are unable to receive additional sperm.[9] Varroa mite's genetic bottleneck is also likely due to its habit of sibling mating.[11]

  • V. destructor protonymph
    V. destructor protonymph
  • Deutonymph of V. destructor
    Deutonymph of V. destructor
  • V. destructor adult male
    V. destructor adult male
  • Varroa mite on bee larva
    Varroa mite on bee larva
  • Varroa mites on pupa
    Varroa mites on pupa
  • Adult female in frontal view
    Adult female in frontal view
  • Adult female in ventral view
    Adult female in ventral view
  • Adult female in dorsal view
    Adult female in dorsal view
  • Adult female mounted for microscopy
    Adult female mounted for microscopy

Host interactions

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Scanning electron microscope image of Varroa mite wedged between bee segments indicated by white arrow.
Close-up scanning electron microscope image of Varroa mite wedged between bee segments.

Adult mites feed on both adult bees and bee larvae by sucking on the fat body, an insect organ that stores glycogen and triglycerides with tissue abundant under epidermis and the surrounding internal body cavity.[5][20][21] As the fat body is crucial for many bodily functions such as hormone and energy regulation, immunity, and pesticide detoxification, the mite's consumption of the fat body weakens both the adult bee and the larva. Feeding on fat body cells significantly decreases the weight of both the immature and adult bee. Infested 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.[4][22][23] Infested bees are more likely to wander into other hives and further increase spread. Bees will occasionally drift into other nearby hives, but this rate is higher for Varroa infested bees.[9][24]

Adult mites live and feed under the abdominal plates of adult bees primarily on the underside of the abdominal 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 thorax, but mites in this location are likely not feeding, but rather attempting to transfer to another bee.[5]

Varroa mites have been found on flowers visited by worker bees, which may be a means by which phoretic mites spread short distances when other bees, including from other hives, visit.[25][26] They have also been found on larvae of some wasp species, such as Vespula vulgaris, and flower-feeding insects such as the bumblebee, Bombus pensylvanicus, the scarab beetle, Phanaeus vindex, and the flower-fly, Palpada vinetorum. There have not been any indications that Varroa mites are able to complete their life cycle on these insects, but instead they become distributed to other areas while a mite is still alive on these insects.[27]

Virus transmission

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Healthy nurse bee (top) and infected bee with deformed wing virus (DWV) (bottom)

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,[5] including RNA viruses such as the deformed wing virus.

Prior to the widespread introduction of Varroa mite, honey bee viruses were typically considered a minor issue. Virus particles are directly injected into the bee's body cavity and mites can also cause immunosuppression that increases infection in host bees. Varroa mites can transmit the following viruses:[4]

Deformed wing virus is one of the most prominent and damaging honey bee viruses transmitted by Varroa mites. It causes crumpled deformed wings that resemble sticks and also causes shortened abdomens.[4][28]

Colony collapse disorder

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Further information: Colony collapse disorder

There is some evidence that harm from both Varroa mite and associated viruses they transmit may be a contributing factor that leads to colony collapse disorder (CCD).[2] While the exact causes of CCD are not known, infection of colonies from multiple pathogens and interaction of those pathogens with environmental stresses is considered by entomologists to be one of the likely causes of CCD.[29][30] Most scientists agree there is not a single cause of CCD.[31]

Management

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Mite populations undergo 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. Mites often invade colonies in the summer, leading to high mite populations in autumn.[32] 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.[33] Various management methods are used for Varroa mite integrated pest management to monitor and manage damage to hives.

Monitoring

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Beekeepers use several methods for monitoring levels of Varroa mites in a colony.[34] They involve either estimating the total number of mites in a hive by using a sticky board under a screen bottom board to capture mites falling from the hive or estimating the number of mites per bee with powdered sugar or an ethanol wash.[35]

Monitoring for mites with a sticky board can be used to estimate the total number of mites in a colony over 72 hours using the equation:

where b is the number of mites found on the sticky board and c is the number of estimated mites in the colony. However, the bee population in a colony also needs to be known to determine what population of mites is tolerable with this method.[35]

Mite counts from a known quantity of bees (i.e., 300 bees) collected from brood comb are instead often used to determine mite severity. Mites are dislodged from a sample of bees using non-lethal or lethal means. The bees are shaken in a container of either powdered sugar, alcohol, or soapy water to dislodge and count mites. Powdered sugar is generally considered non-lethal to honey bees, but lethal methods such as alcohol can be more effective at dislodging mites.[36][35] 3% of the colony being infested is considered an economic threshold damaging enough to warrant further management such as miticides, though beekeepers may use other management tactics in the 0–2% infestation range to keep mite populations low.[35]

Chemical measures

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Honey bee coated with oxalic acid to protect it from mites

Varroa mites can be treated with commercially available acaricides that must be timed carefully to minimize the contamination of honey that might be consumed by humans. The four most common synthetic pesticides used for mite treatments with formulations specific for honey bee colony use are amitraz, coumaphos, and two pyrethroids, flumethrin and tau-fluvalinate, while naturally occurring compounds include formic acid, oxalic acid, essential oils such as thymol and beta acids from hops resin (e.g. lupulone). Many of these products whether synthetic or naturally produced can negatively affect honey bee brood or queens. These products often are applied through impregnated plastic strips or as powders spread between brood frames.[35]

Synthetic compounds often have high efficacy against Varroa mites, but resistance has occurred for all of these products in different areas of the world. Pyrethroids are used because a concentration that will kill mites has relatively low toxicity to honey bees.[35] Compounds derived from plants have also been assessed for mite management. Thymol is one essential oil with efficacy against mites, but can be harmful to bees at high temperatures. Other essential oils such as garlic, oregano, and neem oil have had some efficacy in field trials, though most essential oils that have been tested have little to no effect. Essential oil use is widespread in hives with many of those uses being off-label or in violation of pesticide regulations in various countries. Hop beta acids are lupulones obtained from hop plants and have been used in products marketed for mite control.[35]

Pesticides used for Varroa mite treatment[35]
Chemical Efficacy Notes
Amitraz High (75–90%) Not very affordable; slower occurrence of resistance
Coumaphos Low Use decreased over time because of low efficacy and resistance
Flumethrin High (73–97%) Negative effects to honey bees less severe than tau-fluvalinate
Tau-fluvalinate Low Efficacy lost to resistance; reduced brood survival and queen size
Formic acid High (35–75%) Efficacy varies on the basis of temperature, brood population, and proximity to the chemical within the hive; can cause brood or queen mortality
Oxalic acid High (near 100%) Used during broodless periods only and increases grooming behavior; no known cases of resistance
Thymol Moderate (50–80%) Similar temperature-based issues to formic acid, not effective under 15 °C (59 °F)
Hop beta acids Moderate (43–88%) Low toxicity to humans and bees

Resistance to pyrethroids has occurred in the Czech Republic and the UK as a result of a single amino acid substitution on Varroa mite's genome [citation needed]. In spring 2025, a preprint article attributed the previous year's abnormally high average hive losses of 60% or more to the spread of amitraz-resistant Varroa mites in the United States,[37] with potential mechanisms including another single amino acid substitution.[38] Underlying mechanisms for resistance in other pesticides, such as coumaphos, are still unknown.[39]

Mechanical control

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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.[35]

Screened bottom boards are used both for monitoring and can modestly reduce mite populations by 11–14%. Mites which fall from the comb or bees can land outside the hive instead landing on a solid bottom board that would allow them to easily return to the nest.[35]

Varroa infest drone cells at a higher rate than worker brood cells, so drone cells can be used as a trap for mite removal. Beekeepers can also introduce a frame with drone foundation cells that encourage bees to construct more drone cells. When the drone cells are capped, the frame can be removed to freeze out mites. This labor-intensive process can reduce mite levels by about 50–93%, but if trap cells are not removed early enough before mites emerge, mite populations can spike. This method is only viable in spring and early summer when drones are produced.[35]

Heat is also sometimes used as a control method. The mites cannot survive temperatures near 40 °C (104 °F), but brief exposure to these temperatures do not harm honey bees. Devices are marketed as heat brooding to these temperatures, though the efficacy of many of these products has not been reviewed.[35][40]

Powdered sugar used for estimating mite counts in hives has also been considered for mite management as it or other inert dusts were believed to initiate grooming responses. Long-term studies do not show any efficacy for reducing mite populations.[35]

Genetic methods

[edit]

Honey bee genetics

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Further information: Varroa sensitive hygiene

The Asian honey bee, is more hygienic with respect to Varroa mite than western honey bees, which is in part why mite infestations are more pronounced in western honey bee colonies. Efforts also have been made to breed hygienic honey bees heritable behavior traits, such as those with resistance to Varroa mites. Honey bee lines with resistance include Minnesota Hygienic Bees, Russian Honey Bees, and Varroa sensitive hygiene.[41][42][43]

Hygienic behaviors include [41][44] workers removing pupae heavily infested with mites, which kills both the developing bee and immature mites, and grooming or removal from the brood cell, which increases adult mite mortality. Mites removed from host pupae are at an incorrect life stage to re-infest another pupa. An extended phoretic period in adult female mites has also been noticed.

Hygienic behavior is effective against diseases such as American foulbrood or chalkbrood, but the efficacy of this behavior against mites is not well-quantified; colonies with this behavior alone do not necessarily result in Varroa mite resistant colonies that can survive without miticide treatments. The efficacy of this behavior can vary between bee lines in comparison studies with Minnesota hygienic bees removing 66% of infested pupae, while Varroa sensitive hygiene bees removed 85% of infested pupae. There are minimal trade-off costs to hives that have this hygienic behavior, so it is being actively pursued in bee breeding programs.[41]

Mite genetics

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Researchers have been able to use RNA interference by feeding honey bees mixtures of double-stranded RNA that target expression of several Varroa mite genes, such as cytoskeleton arrangement, transfer of energy, and transcription. This can reduce infestation to 50% without harm to honey bees and is being pursued as an additional control method for Varroa mite.[45][46]

See also

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References

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Revisions and contributorsEdit on WikipediaRead on Wikipedia

Varroa destructor

View on Grokipedia
from Grokipedia
Varroa destructor, commonly known as the Varroa mite, is an ectoparasitic belonging to the family Varroidae that primarily infests the , Apis mellifera. This , measuring 1–1.5 mm in length with a flat, oval body, originated as a parasite of the Eastern honey bee, Apis cerana, but successfully switched hosts to A. mellifera around the mid-20th century, likely in during the 1950s. It represents the single most significant parasitic threat to managed colonies worldwide, contributing to widespread colony losses and economic impacts on apiculture. The biology of V. destructor involves a biphasic life cycle adapted to exploit colonies. In the phoretic phase, adult female mites attach to the bodies of foraging adult bees for dispersal and initial feeding, using their and salivary stylets to pierce the bee's . During the reproductive phase, foundress females invade capped brood cells—preferring drone brood for higher —where they feed and deposit eggs via arrhenotokous , producing up to six offspring per cycle that mature over 6–11 days, with the female progeny mating with the male progeny inside the cell. Contrary to earlier assumptions, V. destructor primarily consumes the host's tissue through extraoral digestion rather than hemolymph alone, leading to profound physiological disruptions including impaired and , reduced immune responses, and heightened susceptibility to environmental stressors. The impacts of V. destructor extend beyond direct feeding, as the mite serves as an efficient vector for viruses, most notably (DWV), which it amplifies and transmits during feeding, exacerbating viral epidemics within colonies. Infested bees exhibit shortened lifespans, deformed wings, diminished ability, and lowered reproductive fitness, while at the colony level, high mite loads (>3% infestation) correlate with rapid and collapse without intervention. This parasite's genetic lability, including hybridization events and rapid evolution of resistance, complicates control efforts, though some stocks show natural or bred resistance through mechanisms like grooming and hygienic behavior. Global spread via trade and migratory has made V. destructor ubiquitous in A. mellifera populations outside isolated regions, underscoring the need for integrated management strategies.

Taxonomy and Morphology

Taxonomy

Varroa destructor belongs to the phylum Arthropoda, class Arachnida, subclass Acari, order , family Varroidae, and genus . This ectoparasitic was originally classified under Varroa jacobsoni following its description by Oudemans in 1904, but in 2000, Anderson and Trueman separated it as a distinct based on analysis revealing multiple haplotypes. The two species share approximately 99.7% nuclear sequence identity, yet differ sufficiently in reproductive compatibility with hosts to warrant distinction. The of V. destructor was sequenced in 2019, revealing close similarity to V. jacobsoni and insights into its parasitic adaptations. Evolutionary origins of V. destructor trace to , where it co-evolved as an of the eastern honey bee, . The first documented host switch to the western honey bee, , occurred around 1952 in eastern , giving rise to the Korean haplotype (also known as the Russia or K1 lineage), which became highly invasive. A similar event in 1957 produced the Japanese haplotype (J or K2 lineage), though less widespread globally. These two haplotypes represent the primary strains capable of reproducing on A. mellifera, driving the mite's global spread. Genetic diversity in invasive V. destructor populations remains low, attributed to serial bottlenecks during colonization, haplodiploid sex determination (where unfertilized eggs develop into haploid males), and prevalent sibling mating within brood cells. This reproductive strategy limits gene flow and heterozygosity, with most variation confined to mitochondrial DNA markers such as the cytochrome c oxidase subunit I (COI) gene, enabling haplotype identification. Prior to 2000, taxonomic confusion with V. jacobsoni obscured the precise timelines of introductions, as reports of "Varroa" infestations worldwide were not differentiated by species or haplotype.

Morphology and Identification

Varroa destructor is an ectoparasitic mite characterized by distinct morphological features across its life stages, which facilitate identification in apicultural and settings. The adult female, the most commonly observed stage, exhibits a reddish-brown to dark brown coloration and an oval, dorsoventrally flattened body adapted for attachment beneath honey bees. This body measures 1.0–1.8 mm in length and 1.5–2.0 mm in width, with a curved dorsal shield that allows it to wedge between the host's abdominal plates. The female possesses eight legs bearing ambulacra with strong claws for clinging to the bee's , and specialized as piercing stylets for feeding on host tissue via extraoral digestion; notably, it lacks eyes, relying instead on chemosensory structures for host location. The mite undergoes several developmental stages within the sealed brood cell of its host. The protonymph emerges from the egg as a non-feeding, transparent white larva approximately 0.3 mm long, featuring eight short legs, pointed , and no discernible sexual differences without . It molts into the deutonymph stage, which is larger (up to 0.8 mm), white to pale tan, and actively feeding on the brood's ; this stage develops genital papillae and ambulacra but remains confined to the cell unless dispersal occurs rarely. Adult males, arising from unfertilized eggs, are pale, smaller (0.7 mm long by 0.6 mm wide), and non-feeding, with a more rounded, triangular body shape, longer legs relative to body size, and degenerate unsuitable for piercing; they are short-lived and never leave the brood cell. Sexual dimorphism is pronounced, with females being larger, more pigmented, and robust for phoresy and reproduction, while males are pale, diminutive, and adapted solely for mating within the cell. Identification of V. destructor relies on these morphological traits, particularly the chelicerae and ambulacra, which distinguish it from other bee mites like Tropilaelaps species through microscopic examination. However, due to its close similarity to Varroa jacobsoni, definitive species confirmation often requires DNA-based methods, such as PCR amplification of mitochondrial markers like cytochrome c oxidase subunit I, to differentiate the two cryptic species.

Distribution and Hosts

Geographic Distribution

Varroa destructor is native to Southeast Asia, where it primarily parasitizes the eastern honey bee, Apis cerana, with the earliest description recorded in Java in 1904. The mite's host shift to the western honey bee, Apis mellifera, occurred following the introduction of this species to Asia in the mid-20th century, enabling its initial spread beyond its native range. The first documented invasion into Europe began in the 1960s, starting in eastern regions such as Bulgaria in 1963 and spreading westward through the Soviet Union and into Western Europe by the 1970s and 1980s. In the Americas, the mite arrived in South America around 1971, likely via Brazil, and reached North America in the late 1970s to early 1980s, with confirmed detections in the United States by 1987. By the 1990s, it had established across much of Asia outside its native range, North and South America, Europe, and parts of Africa, including North Africa around 1990 and South Africa in 1997, affecting at least 31 African countries by 2020. The global dissemination of V. destructor has been facilitated primarily by human activities, including the international trade of honey bee colonies, queens, and contaminated equipment, as well as natural dispersal through swarming and drifting bees. Migratory beekeeping practices have accelerated its spread within continents, while long-distance transport via ships or aircraft has enabled intercontinental invasions. Historical data prior to 2000 is complicated by widespread misidentification of the mite as Varroa jacobsoni, a related species; molecular studies in 2000 clarified V. destructor as the primary invader of A. mellifera hives worldwide, refining our understanding of its invasion pathways. By 2020, V. destructor was established on every continent except isolated regions, with widespread presence in North and South America, , , and much of . As of 2025, it remains absent from certain isolated areas, including , the , , and some Pacific islands (such as the ), due to stringent protocols. A significant recent development occurred in , where the was first detected in in June 2022 at the , leading to an initial emergency eradication effort that transitioned to long-term management by September 2023 due to confirmed establishment. By November 2025, infestations had spread to , , Victoria, , and the Australian Capital Territory, prompting a transition to a national management program to build resilience until at least February 2026.

Primary and Secondary Hosts

Varroa destructor primarily parasitizes the Western honey bee (Apis mellifera), a host to which the mite shifted in the mid-20th century, resulting in high susceptibility due to the absence of long-term co-evolutionary adaptations. This mismatch allows the mite to reproduce successfully in both drone and worker brood cells of A. mellifera, leading to rapid population growth and severe colony damage. In contrast, the original and secondary natural host, the Eastern honey bee (Apis cerana), exhibits tolerance through behavioral defenses such as grooming and hygienic brood removal, which limit mite reproduction primarily to drone brood cells. Experimental infestations and field observations indicate that V. destructor can parasitize other Apis species, including Apis dorsata, where both phoretic and reproductive phases occur, with nymph stages observed in brood cells confirming successful reproduction. The mite has also been recorded in the phoretic phase on bumblebees (Bombus spp.), but reproduction is absent on non-Apis hosts due to incompatible brood development cycles. Within A. mellifera colonies, V. destructor shows a strong preference for drone brood over worker brood, infesting drone cells at rates 8–10 times higher, attributed to the longer pre-capping period (40–50 hours versus 15–20 hours) that allows more time for invasion and higher reproductive success. During the phoretic phase, mites preferentially attach to nurse bees, which frequently visit brood cells, facilitating transport to suitable reproductive sites. The co-evolutionary history with A. cerana has fostered a balanced host-parasite relationship, where mite populations remain low through host defenses, whereas A. mellifera lacks these mechanisms, resulting in exponentially higher infestation rates and vulnerability.

Life Cycle and Reproduction

Phoretic Phase

The phoretic phase represents the non-reproductive dispersal stage in the life cycle of Varroa destructor, during which adult female mites attach to honey bees for transport within and between colonies. This phase typically lasts 4.5 to 11 days when brood is present during the brood-rearing season, allowing mites to seek opportunities for reproduction; however, in the absence of brood during winter, it can extend up to five to six months as mites enter a state of diapause. Mites preferentially cling to nurse bees, which frequent brood areas, using specialized ambulacral structures on their pretarsi for secure attachment to the bee's exoskeleton, often on the abdomen or thorax. During this period, mites feed sporadically on the host's fat body tissue by piercing the intersegmental membrane and using extraoral digestion to liquefy and consume the tissue, sustaining themselves while minimizing host detection. This phoretic attachment facilitates the mite's dispersal role, enabling spread from hive to hive through natural bee behaviors such as drifting (unintentional movement between colonies), robbing ( on weakened hives), and swarming (colony reproduction). Mites detach from their host upon the bee's death, rapidly seeking a new carrier to avoid , which underscores the phase's reliance on host vitality for mite survival. In winter, reduced bee activity and clustering lead to higher mite mortality, as fallen hosts provide fewer opportunities for reattachment compared to active seasons. The average lifespan of phoretic female V. destructor is approximately 27 days when brood is available, reflecting the phase's integration with reproductive opportunities; without brood access, longevity extends but at the cost of increased mortality risks. Transition to the reproductive phase occurs when a mite detaches from its phoretic host to invade an uncapped brood cell suitable for oviposition.

Reproductive Phase

The reproductive phase of Varroa destructor occurs within the capped brood cells of honey bees, where a fertile female mite, known as the foundress, invades and completes her reproductive cycle. The foundress enters an uncapped brood cell containing a fifth-instar , typically 15–20 hours before capping in worker cells or 40–50 hours before capping in drone cells, allowing her to become trapped with the developing upon sealing. This invasion is selective, with the mite preferring drone brood due to its larger size, longer developmental period, and attractive chemical cues from the . Once the cell is capped, the foundress activates her ovaries after feeding on the tissue of the host and lays her first unfertilized , which develops into a male, approximately 60–70 hours post-capping. She then deposits 3–5 fertilized eggs at intervals of about 30 hours each, resulting in a total of 4–6 eggs per cycle, with subsequent eggs producing females. Development from to adult takes 5.8 days for females and 6.6 days for males, enabling the production of 2–5 mated daughter mites per foundress under optimal conditions. The foundress exhibits maternal care by creating a single feeding site—a in the pupa's , usually on the fifth abdominal segment—through which all , including herself, access the host's tissue via extraoral digestion. She positions her near this site to facilitate their feeding, though the nymphs consume host fluids directly rather than through regurgitation. Males emerge first and remain in the cell, with their emerging sisters at the fecal site using spermatophores; bouts last 3–6 minutes, and males typically die shortly after, while mated females prepare to emerge with the host . Fecundity varies by host brood type, with up to 5 possible in worker cells (yielding 1.3–1.7 viable daughters on average) and up to 6–7 in drone cells (yielding 2–3 viable daughters), owing to the extended development time in drones that permits more egg-laying opportunities. is notably higher in Apis mellifera than in the original host , where reproduction is largely restricted to drone cells due to shorter worker brood cycles, aggressive grooming, and rapid cell uncapping behaviors that suppress mite proliferation.

Pathogenesis and Interactions

Feeding and Physiological Effects

Varroa destructor employs its to pierce the soft intersegmental membrane of the bee's abdomen, creating an open through which it injects containing anticoagulants and enzymes to suppress host healing and facilitate feeding. The mite primarily consumes tissue rather than , using a muscular to ingest fluid at a rate of approximately 1 μl per day based on volume measurements. This feeding occurs repeatedly on the same site, maintaining the wound open for extended periods during both phoretic and reproductive phases. Feeding by V. destructor directly impairs physiology, leading to reduced body weight and impaired immune responses in infested individuals. Adult workers parasitized by the mite exhibit shortened lifespans, with studies showing up to a 50% reduction compared to uninfested bees. These effects compromise foraging efficiency and overall colony labor force. In brood, V. destructor infestation causes retarded pupal development and diminished size of hypopharyngeal glands in newly emerged nurse bees, reducing their capacity for production. Infested pupae experience slowed growth and lower emergence weights, exacerbating nutritional deficits across generations. Even low infestation levels, such as 1–2 mites per brood cell, inflict significant physiological harm, including elevated mortality and sublethal impairments. Over multiple generations, these cumulative effects weaken the entire by progressively diminishing vitality and reproductive output, ultimately leading to . V. destructor exhibits a for drone brood, amplifying damage in this reproductive stage. Infested brood often develop high levels of deformed wing virus (DWV), leading to physical deformities such as shortened abdomens and malformed wings in emerging adults.

Transmission Dynamics

Varroa destructor spreads within colonies primarily through phoresy, where adult female s attach to worker bees, particularly nurse bees, to facilitate movement across the hive. During the phoretic phase, s preferentially infest middle-aged nurse bees that tend to late-stage brood, enabling them to access suitable brood cells for and thereby perpetuating intra-colony transmission. High transmission rates occur in dense clusters of nurse bees, where close physical contact among bees increases opportunities for mite transfer between individuals. Additionally, interactions during grooming behaviors, such as autogrooming or allogrooming, can inadvertently contribute to mite dispersal if s are not fully dislodged, allowing them to reattach to nearby bees. Between colonies, V. destructor is transmitted via several mechanisms involving bee mobility and human activities. Drifting worker , which mistakenly enter neighboring , carry phoretic mites and significantly contribute to inter-colony spread, especially in apiaries with high colony densities. Robbing from stronger colonies invade weakened ones, acquiring mites in the process and transporting them back to their home , a phenomenon exacerbated during periods of resource scarcity. Swarming events also facilitate transmission, as emerging swarms can distribute a portion of the mite population from the parent to new sites. Contaminated beekeeping equipment, such as or tools moved between apiaries without proper sanitation, serves as another vector for mite transfer. Secondary vectors include flowers, where dislodged mites can survive briefly and reattach to foraging from different colonies. The rate of V. destructor infestation is influenced by seasonal factors and colony dynamics, leading to rapid population increases during active brood-rearing periods. In summer, mite populations can double every 3–4 weeks due to multiple reproductive cycles synchronized with brood production, resulting in tied to the availability of brood cells. This growth is descriptive of the 's reproductive potential, where each cycle amplifies the phoretic population for further dispersal. During winter, clustering of reduces overall mite mobility but concentrates transmission within the tight-knit bee mass, potentially sustaining infestations despite lower brood availability.

Associated Diseases and Impacts

Virus Transmission

_Varroa destructor serves as a primary vector for several honey bee viruses, most notably Deformed wing virus (DWV), Acute bee paralysis virus (ABPV), and Kashmir bee virus (KBV). These viruses, along with at least five others such as Israeli acute paralysis virus (IAPV) and Slow bee paralysis virus (SBPV), are transmitted through two main routes: fecal-oral contamination during mite defecation on brood cells or adult bees, and direct injection into the host's hemolymph during feeding. Transmission efficiency varies by virus; for instance, KBV-positive mites transfer the virus to bee pupae in approximately 70% of cases, while virus-free mites can acquire KBV through close contact with infected mites. The mechanism of transmission begins with mites acquiring viruses from the hemolymph of infected bees during feeding. Subsequently, the mites inject viral particles directly into new hosts via their salivary secretions, bypassing external barriers and enabling rapid systemic . For DWV specifically, the virus replicates within the mite's salivary glands, amplifying viral titers up to 357-fold and facilitating higher doses during subsequent feedings on developing pupae. This injection route contrasts with purely oral transmission and enhances , as evidenced by studies showing active DWV replication in V. destructor, altering evolutionary dynamics and increasing viral loads in both mites and bees. Varroa-mediated virus transmission induces immunosuppression in honey bees by depleting hemolymph resources and upregulating viral replication, weakening innate immune responses such as antimicrobial peptide production. Prior to V. destructor's global spread, these viruses typically caused benign or low-level infections in honey bees; however, mite vectoring has transformed them into highly pathogenic agents, leading to severe symptoms like wing deformities and paralysis. In heavily infested colonies, this synergy results in elevated mortality, with DWV-positive colonies harboring ≥1 mite per 100 bees facing 3.46 times higher winter mortality odds compared to less infested ones, and transmission rates for certain viruses reaching 50–90% in pupae. Recent 2025 research highlights co-transmission dynamics of IAPV with DWV, revealing variable mortality outcomes in co-infected bees depending on seasonal factors and mite infestation levels, underscoring the mite's role in exacerbating multi-virus epidemics. Currently, no commercial vaccines exist for these bee viruses, though experimental approaches like (RNAi) targeting viral genes—such as DWV structural proteins—have shown promise in reducing infection loads and bee mortality in lab and field trials.

Contribution to Colony Collapse Disorder

_Varroa destructor plays a central role in by acting as a primary driver through the escalation of viral infections in colonies. The mite's feeding suppresses bee immunity, facilitating the rapid spread of debilitating viruses that lead to symptoms characteristic of CCD, including the sudden disappearance of adult worker bees and neglect of brood care. Research indicates that infestations exceeding 3% of adult bees correlate strongly with the onset of these collapse symptoms, as high mite loads overwhelm colony resilience and trigger cascading health failures. CCD is a multifactorial syndrome where Varroa interacts synergistically with other stressors such as exposure and nutritional deficiencies to precipitate colony failure. Studies demonstrate that Varroa-free populations experience CCD at much lower rates compared to infested ones, underscoring the mite's pivotal contribution to the disorder's severity. For instance, in prior to the 2022 detection of Varroa, colony collapse events resembling CCD were rare, highlighting the mite's necessity for the 's full manifestation. The surge in CCD cases beginning in 2006 across the and coincided with the widespread establishment and intensification of Varroa infestations in managed hives. Recent 2025 data from U.S. beekeeping surveys report over 60% colony losses in commercial operations, with unmanaged Varroa infestations identified as a key factor in these declines, particularly amid emerging mite resistance to common acaricides. Economically, Varroa-driven losses threaten billions in annual U.S. agricultural value, as honey bee pollination supports over $15 billion in crop production; unmanaged infestations amplify these stressors, resulting in hundreds of millions in direct replacement and production costs each year.

Control and Management Strategies

In Italy, as of February 2026, no new specific guidelines have been issued for 2026 regarding the management of Varroa destructor in beekeeping. The reference national guidelines remain the "Linee guida per il controllo dell'infestazione da Varroa destructor – 2025", issued by the Ministero della Salute through the Centro di Referenza Nazionale at the Istituto Zooprofilattico Sperimentale delle Venezie (IZSVe), and applicable to the 2025/2026 beekeeping season. These guidelines promote an integrated pest management (IPM) approach: regular monitoring of infestation levels through phoretic Varroa counts on adult bees, mechanical and biotechnical methods (such as brood interruption and selection of resistant bees), and chemical treatments using authorized products only when necessary, with particular emphasis on autumn-winter interventions to reduce mite infestation before winter. For beginner beekeepers, attendance at training courses, weekly monitoring, timely interventions, and consultation with local beekeeping associations or Aziende Sanitarie Locali (ASL) are recommended to comply with sanitary norms and authorizations. The objectives are sustainability, bee health, and the quality of bee products.

Monitoring Methods

Monitoring Varroa destructor infestations is essential for integrated pest management in honey bee colonies, as timely detection allows beekeepers to intervene before mite populations reach damaging levels. Common techniques focus on sampling adult bees or observing natural mite fall to estimate infestation rates, typically expressed as the percentage of mites per 100 bees or daily drop counts. These methods balance accuracy, cost, and non-lethality, with recommendations to sample at least 300 bees or monitor multiple colonies per apiary for reliable data. Sticky boards placed under screened bottom boards capture naturally falling mites, providing a non-invasive estimate of through daily or 24-hour drop counts. For a standard 10-frame hive, a threshold exceeding 59 mites per 24 hours indicates the need for action, as this correlates with rising populations during brood-rearing periods. This method is simple and inexpensive but less precise for low-level infestations, as it misses phoretic mites still attached to bees. The alcohol wash remains the gold standard for accuracy, involving the submersion of a 300-bee sample in 70% or soapy water, followed by shaking and straining to count dislodged , achieving near-complete recovery rates often exceeding 95% compared to less reliable alternatives. A typical threshold is 3 per 100 bees, though seasonal adjustments apply: below 1% in spring and 2% during the rest of the year to maintain colony health. While lethal to the sample, its precision makes it ideal for quantifying mean mite abundance in apiaries with many colonies, where sampling 20% of suffices. For a non-lethal option, the roll coats a 300-bee sample with two tablespoons of powdered sugar, dislodging mites through vigorous shaking over a screen for counting, with a similar 2% threshold for treatment. This technique recovers approximately 90% of mites relative to alcohol washes but is affected by factors like and nectar flow, making it less reliable in certain conditions. In-hive brood frame inspections complement these by visually checking for mites on pupae, particularly in drone brood where infestations are higher due to extended development times. Monitoring should occur monthly during peak brood-rearing seasons (spring through fall) to track , with economic thresholds of 1–3% infestation rates aimed at preventing winter losses that can exceed 50% in unmanaged apiaries. These levels tie to V. destructor's reproductive potential, where early detection avoids . Recent advances in 2025 include AI-powered digital apps and scanners for automated counting, such as the BeeVS system, which analyzes images from sticky sheets using neural networks to detect mites with error rates below 1% for loads over 10 mites, enabling rapid, repeatable assessments across large apiaries. Predictive platforms integrate wireless sensors and (e.g., ViT models with 98.6% accuracy) for real-time infestation forecasting and what-if , reducing manual labor while supporting scalable management.

Chemical Control

Chemical control of Varroa destructor primarily involves synthetic and organic acaricides applied to honey bee colonies to reduce mite populations. These treatments target phoretic and reproductive mites but require careful management to maintain efficacy and minimize risks to bees and hive products. Common approaches include strips, pads, dribbles, and vapors, with selection influenced by regional regulations, mite resistance levels, and seasonal conditions. Amitraz, a synthetic formamidine delivered via plastic strips (e.g., Apivar), remains a widely used treatment with reported efficacies up to 95% under optimal conditions. However, resistance has emerged globally, including , where the Y215H in the mite's receptor has been associated with resistance in a high proportion (e.g., 88.5%) of samples from resistant populations, rendering amitraz ineffective in affected . Rotation with other modes of action is essential to delay further resistance development. Organic acids like and offer effective alternatives with lower resistance risks. Formic acid, applied via pads or vapor (often combined with propolis for stability), achieves 80–90% mite kill rates, though efficacy varies with temperature and brood presence. , administered as a dribble or vapor, yields 90–99% efficacy specifically in broodless periods, such as winter, but shows reduced performance with active brood. No widespread resistance to these acids has been confirmed, making them valuable for integrated programs. Pyrethroids, such as tau-fluvalinate (e.g., Apistan strips), were among the first chemical controls introduced but are now largely ineffective due to resistance that developed in the 1990s across , including in the and , where point in the mite's gene confer tolerance. Their use is discouraged in resistant areas to avoid selecting for additional . Application timing is critical for maximizing impact and minimizing bee stress; for instance, oxalic acid treatments are most effective during broodless phases to target phoretic mites. Rotating acaricides with distinct mechanisms—such as alternating amitraz with organic acids—helps manage resistance, as recommended by guidelines. Organic approvals for formic, oxalic, and thymol-based products vary by region, with many certified for use in and under standards like organic regulations. Potential risks include chemical residues in and , which can accumulate from repeated applications and affect health or marketability; for example, amitraz residues have been detected in comb at levels up to 0.1 mg/kg post-treatment. Recent thymol-based formulations, such as low-dose nanoemulsions, have gained traction as resistance-mitigating alternatives, offering 70–90% efficacy with reduced residue concerns compared to synthetics.

Physical and Cultural Controls

Physical controls for Varroa destructor involve mechanical interventions that exploit the mite's to prevent or facilitate removal without chemical agents. Screened bottom boards replace solid hive floors with mesh screens, allowing phoretic mites to fall out of the hive while retaining and preventing re-entry, thereby reducing mite populations in . Studies indicate these boards can decrease mite levels by up to 25% when used consistently, though efficacy varies with and must be paired with other methods to prevent economic thresholds from being exceeded. Drone comb traps leverage the 's preference for drone brood, where females produce up to 2.6 offspring per cell compared to 1.4 in worker cells. Beekeepers insert drone foundation frames into the brood nest during spring or summer, allowing the queen to lay drone eggs; once capped (around days 18-24), the frame is removed and the infested brood destroyed by freezing or burning. This method typically reduces mite populations by 40-50% over two cycles per season and up to 90% when combined with a broodless period. Cultural practices focus on hive management to disrupt mite reproduction cycles and limit spread. Brood breaks, induced by caging the queen for approximately three weeks using devices like Scalvini cages, halt larval production and force mites into the vulnerable phoretic stage on adult bees, where they are more susceptible to natural grooming or removal. This approach can significantly lower mite numbers by slowing reproduction, with recovery typically occurring within two months, though it requires careful timing to avoid stressing the . The use of small-cell combs, with cell diameters reduced to 4.9 mm from the standard 5.4 mm, aims to shorten the post-capping period and potentially increase immature mortality due to spatial constraints. However, scientific evaluations have found no significant impact on total brood area, mites per brood cell, or overall populations, with levels remaining comparable to standard combs across trials. Efficacy remains disputed, offering minimal benefit under typical conditions. Promoting bee hygiene through cultural means enhances natural grooming behaviors to dislodge mites. Applying powdered sugar dust to bee clusters stimulates auto-grooming, prompting workers to remove and drop mites from their bodies, providing a non-invasive way to reduce infestations in lightly affected colonies. Additionally, increasing apiary spacing to at least 100 meters between hives minimizes bee drift, which spreads phoretic mites; closer spacings (0-10 meters) result in 50-60% higher average mite counts due to increased inter-colony movement. These physical and cultural controls are most effective when integrated into a monitoring program, such as regular alcohol washes or sticky board counts to keep infestations below 2 mites per 100 bees, particularly in low-infestation scenarios. While labor-intensive due to frequent interventions like frame removals or queen caging, they support by reducing reliance on other strategies and maintaining health without residues.

Biological and Genetic Controls

Biological controls for Varroa destructor primarily involve leveraging natural enemies or enhancing host resistance through of honey bees. Hygienic stocks, such as the Hygienic line, have been developed to promote the removal of mite-infested pupae by worker bees, achieving removal rates exceeding 40% in naturally infested brood cells, which contributes to a substantial reduction in mite populations. Similarly, Sensitive Hygiene (VSH) breeding programs select for bees that uncap and remove infested worker brood, with efficacy reaching up to 70% in disrupting mite reproduction under controlled conditions, as demonstrated in USDA evaluations where VSH colonies maintained low infestation levels without chemical interventions for over two decades. These traits are heritable and integrated into commercial breeding lines, though they require ongoing selection to maintain expression amid . Genetic approaches target the mites directly using (RNAi), where double-stranded RNA (dsRNA) sprays silence essential mite genes, such as , leading to up to 50% reduction in female mite reproduction in laboratory trials by inhibiting egg laying and progeny viability. Field applications, including sugar syrup feeders delivering dsRNA targeting genes like , have shown 33–42% reductions in phoretic mite infestations compared to controls, with no adverse effects on . CRISPR-Cas9 editing remains experimental as of 2025, primarily used to validate resistance mutations in mite genes like the β-adrenergic-like receptor, but holds potential for future targeted disruptions in mite reproduction without affecting bees. Other biological agents, such as entomopathogenic fungi, offer limited field success. Strains of Metarhizium anisopliae, applied via spore-coated strips or dusts, achieve 20–50% mite mortality through mycosis in colonies, with evolved variants (e.g., JH1078) providing control comparable to mild chemical treatments for up to five weeks, though varies with and hive . Predatory mites like have been tested for direct predation on V. destructor, but remain unviable for widespread use due to inconsistent establishment in hives and minimal long-term population suppression. As of 2025, RNAi-based varroacides like Norroa (vadescana dsRNA) have been registered by the EPA following U.S. field trials, demonstrating up to 18 weeks of control and improved in multi-regional studies. Breeding programs in the U.S. (e.g., USDA VSH and low-Varroa growth lines) and (e.g., native selection) have yielded 20–30% of tested lines with sustained resistance, characterized by lower infestation rates and reduced prevalence under pressures. These efforts emphasize integrated genetic resistance to minimize reliance on short-term interventions.

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