Varroa
Varroa is a genus of parasitic mites in the family Varroidae, order Mesostigmata, class Arachnida, known for species that infest honey bees of the genus Apis.<grok:render type="render_inline_citation">Taxonomy and Description
Genus Overview
Varroa is a genus of parasitic mites belonging to the family Varroidae in the order Mesostigmata, class Arachnida, and phylum Arthropoda, primarily parasitizing species of the honey bee genus Apis.[6] The genus name derives from the Roman scholar Marcus Terentius Varro (116–27 BCE), who documented bee pests in his agricultural writings, Rerum Rusticarum.[7] These mites represent a severe threat to global apiculture, as they weaken honey bee colonies by feeding on their fat bodies (a nutrient-rich tissue)[8] and transmitting debilitating viruses, contributing significantly to colony collapse disorder (CCD)._ [9] The economic toll is substantial, with Varroa infestations linked to billions of dollars in annual losses worldwide due to reduced pollination services and colony replacements.[9] For instance, in the United States during 2024–2025, beekeepers reported the loss of approximately 1.6 million managed colonies, largely attributed to Varroa-related factors.[10] The most economically impactful species within the genus is Varroa destructor, which causes the disease known as varroosis in Apis mellifera colonies.[11]Morphology
The adult female Varroa mite possesses an oval, dorsoventrally flattened body, typically measuring 1.00–1.77 mm in length and 1.50–1.99 mm in width, with a reddish-brown coloration that darkens with age and feeding.[9] This flattened shape allows the mite to fit snugly between the abdominal sclerites of its honey bee host.[9] The chelicerae are specialized piercing structures used to penetrate host tissue for feeding on fat body tissue.[9][8]_ The mite has four pairs of ambulatory legs, each terminating in claws and empodia that provide strong adhesion for clinging to the host's exoskeleton during phoretic dispersal.[9] Sexual dimorphism is evident in Varroa mites, with adult males being considerably smaller at 0.75–0.98 mm in length, pale yellowish in color, and spherically shaped with longer, more slender legs compared to females.[9][12]_ Males are non-feeding, relying on nutrients acquired during the nymphal stage, and have a short lifespan of only a few days; their chelicerae are modified into structures suited for sperm transfer rather than piercing.[12] Key anatomical adaptations support the mite's parasitic lifestyle, including peritremes for respiration—chitinized, elongated structures located laterally above the third pair of coxae that surround the stigma and facilitate gas exchange even when submerged in host fluids.[13] In females, a genital orifice on the ventral surface, positioned between the base of the fourth pair of legs, enables egg deposition during reproduction.[14] Ventral setae and the leg empodia further aid phoretic behavior by enhancing grip on adult bees for transport between hosts.[9] The developmental stages of Varroa mites show progressive morphological changes. Protonymphs are circular and transparent white, measuring approximately 0.63–0.68 mm in length and 0.74–0.78 mm in width, with eight functional legs and pointed chelicerae; at this stage, the cuticle is soft and unsclerotized, and males and females are indistinguishable externally without dissection.[15] [9] Deutonymphs adopt an oval shape similar to adults, growing to 1.0–1.2 mm in length and 1.1–1.7 mm in width, with increased sclerotization of the exoskeleton for rigidity and reduced setae density compared to protonymphs, marking the final preparatory phase before the adult molt.[15] [9]Species
The genus Varroa comprises four recognized species that parasitize honey bees, primarily in the genus Apis, with distinct host preferences and geographic ranges shaped by historical host-switching events. These species were delineated through morphological and molecular analyses, particularly mitochondrial DNA sequencing of the CO-I gene, revealing genetic distinctions among haplotypes previously grouped under V. jacobsoni.[16] No new species have been described since 2000, though ongoing genetic studies identify variants within V. destructor associated with host resistance mechanisms in bees.[17] The following table summarizes the four species, their primary hosts, and key geographic associations:| Species | Primary Hosts | Geographic Distribution |
|---|---|---|
| V. destructor | A. cerana (native), A. mellifera (adapted via host-switching) | Cosmopolitan in regions with A. mellifera colonies; native to Asia; absent from some isolated areas such as Western Australia and certain islands as of 2025.[18] [19] |
| V. jacobsoni | A. cerana (specific); limited records on A. mellifera in Papua New Guinea | Southeast Asia (e.g., Indonesia, Philippines, Malaysia); introduced to Papua New Guinea.[16] [20] |
| V. rindereri | A. koschevnikovi | Borneo (Indonesia and Malaysia)._ [21] |
| V. underwoodi | A. cerana | South Asia (India, Nepal); also reported in far eastern Russia, South Korea, and parts of Indonesia.[16] [22] |