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Mites are small arthropods belonging to the class Arachnida and the subclass Acari (also known as Acarina). The term "mite" refers to the members of several groups in Acari but it is not a precise scientific taxon and excludes the ticks, order Ixodida. The scientific discipline devoted to the study of ticks and mites is called acarology.

Mite
Peacock mite, Tuckerella sp.jpg
Peacock mite (Tuckerella sp.),
false-colour SEM, magnified 260×
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Subphylum: Chelicerata
Class: Arachnida
Subclass: Acari
Leach, 1817
Superorders
The microscopic mite Lorryia formosa (Tydeidae)

Most mites are tiny, less than 1 mm (0.04 in) in length, and have a simple, unsegmented body plan. Some species live in water, many live in soil as decomposers, others live on plants, sometimes creating galls, while others again are predators or parasites. This last group includes the commercially important Varroa mites of honey bees, and the scabies mite of humans.

Contents

Phylogeny and taxonomyEdit

The term "mite" is not a precise scientific taxon but is used to refer to the members of several groups in the subclass Acari. The phylogeny of the Acari is under dispute and several taxonomic schemes have been proposed for their classification.

TaxonomyEdit

The third edition (2009) of the standard textbook A Manual of Acarology uses a system of six orders, grouped into three superorders:[1]

  • Superorder Opilioacariformes – a small order of large mites that superficially resemble harvestmen (Opiliones), hence their name
  • Superorder Parasitiformes – ticks and a variety of mites
  • Superorder Acariformes – the most diverse group of mites
    • Trombidiformes – plant parasitic mites (spider mites, peacock mites, gall mites, red-legged earth mites, etc.), snout mites, chiggers, hair follicle mites, velvet mites, water mites, etc.
    • Sarcoptiformes
      • Oribatida – oribatid mites, beetle mites, armored mites (also cryptostigmata)
      • Astigmatina – stored product, fur, feather, dust, and human itch mites, etc.

PhylogenyEdit

Thus members of the superorders Opilioacariformes and Acariformes (sometimes known as Actinotrichida) are mites, as well as some of the members of Parasitiformes (sometimes known as Anactinotrichida).[2] Recent genetic research has caused a change in the naming scheme, however, and recent publications have changed the superorder Parasitiformes to an order.[3] Other recent research has suggested that Acari is polyphyletic, with ticks and spiders being more closely related than ticks and mites.[4] The cladogram is based on Dabert et al 2010, which used molecular data. It shows the Acariformes sister to the Solifugae (camel spiders), while the Parasitiformes were sister to the Pseudoscorpionida.[5]

part of Arachnida


Solifugae (camel spiders)

  


Parasitiformes (parasitic mites, ticks)

 Ixodida (ticks)   



 Parasitic mites, inc. Varroa  







Acariformes (other mites)

 Trombidiformes (chiggers, gall & velvet mites, etc)   



 Sarcoptiformes (dust mites, fur mites, etc)  


 

Pseudoscorpionida (false scorpions)

  





"Acari" (mites and ticks)

AnatomyEdit

Mites are tiny members of the class Arachnida; most are in the size range 0.25 to 0.75 mm (0.01 to 0.03 in) but some are larger and some are no bigger than 0.1 mm (0.004 in) as adults. The body plan is similar to that of ticks in having two tagmata, a prosoma or cephalothorax, and an opisthosoma or abdomen. Segmentation has almost entirely been lost and the prosoma and opisthosoma are fused, with the positioning of the limbs indicating the location of the original parts of the body.[6]

 
1 Chelicerae, 2 Palps, 3 Salivary glands, 4 Gut, 5 Excretory (Malpighian) tubules, 6 Anus, 7 Ovary or testes, 8 Air-breathing tubes (tracheae), 9 Central ganglion, 10 Legs, 11 Hypostome.[7]

At the front of the body is the gnathosoma or capitulum. This is not a head and does not contain the eyes or the brain, but is a retractable feeding apparatus consisting of the chelicerae, the pedipalps and the oral cavity. It is covered above by an extension of the body carapace and is connected to the body by a flexible section of cuticle. The mouthparts differ between taxa depending on diet; in some species the appendages resemble legs while in others they are modified into chelicerae-like structures. The oral cavity connects posteriorly to the mouth and pharynx.[6]

Most mites have four pairs of legs, each with six segments, which may be modified for swimming or other purposes. The dorsal surface of the body is clad in hardened tergites and the ventral surface by hardened sclerites; sometimes these form transverse ridges. The gonopore (genital opening) is located on the ventral surface between the fourth pair of legs. Some species have one to five median or lateral eyes but many species are blind, and slit and pit sense organs are common. Both body and limbs bear setae (bristles) which may be simple, flattened, club-shaped or sensory. Mites are usually some shade of brown, but some species are red, orange, black or green, or some combination of these colours.[6]

Internal organsEdit

Mites have a typical arachnid digestive system, although some species lack an anus. The circulatory system consists of a network of sinuses and lacks a heart, movement of fluid being driven by the contraction of body muscles. Gas exchange is carried out across the body surface, but many species additionally have between one and four pairs of tracheae, the spiracles being located in the front half of the body. The excretory system includes a nephridium and one or two pairs of Malpighian tubules.[6]

Reproduction and life cycleEdit

The sexes are separate in mites; males have a pair of testes in the mid-region of the body, each connected to the gonopore by a vas deferens, and in some species there is a chitinous penis; females have a single ovary connected to the gonopore by an oviduct, as well as a seminal receptacle for the storage of sperm. In most mites, sperm is transferred to the female indirectly; the male either deposits a spermatophore on a surface from which it is picked up the female, or he uses his chelicerae or third pair of legs to insert it into the female's gonopore. In some of the Acariformes, insemination is direct using the male's penis.[6]

The eggs are laid in the substrate, or wherever the mite happens to live. They take from two to six weeks to hatch, and the first stage larvae have six legs. After three moults, the larvae become protonymphs, with eight legs, and after a further three moults, they become adults. Longevity varies between species, but the lifespan of mites is short as compared to many other arachnids.[6]

DiversityEdit

 
Lime nail galls on Tilia × europaea, caused by the mite Eriophyes tiliae

Mites are among the most diverse and successful of all the invertebrate groups. They have exploited a wide array of habitats, and because of their small size (most are micro-animals), go largely unnoticed. They are found in fresh and salt water, in the soil, in forests, pastures, agricultural crops, ornamental plants, thermal springs and caves. They inhabit organic debris of all kinds and are extremely numerous in leaf litter. They feed on animals, plants and fungi and some are parasites of plants and animals.[8] Some 48,200 species of mites have been described,[9] but there may be a million or more species as yet undescribed.[6]

DispersalEdit

Being unable to fly, mites need some other means of dispersal. On a small scale, walking is used to access other suitable locations in the immediate vicinity. Some species mount to a high point and adopt a dispersal posture and get carried away by the wind, while others waft a thread of silk aloft to balloon to a new position.[10]

Parasitic mites use their hosts to disperse, and spread from host to host by direct contact. Another strategy is phoresy; the mite, often equipped with suitable claspers or suckers, grips onto an insect or other animal, and gets transported to another place. It is just a hitch-hiker and does not feed during the time it is carried by its temporary host. These travelling mites are mostly species that reproduce rapidly and are quick to colonise new habitats.[10]

EcologyEdit

Mites occupy a wide range of ecological niches. For example, Oribatida mites are important decomposers in many habitats. They eat a wide variety of material including living and dead plant and fungal material, lichens and carrion; some are predatory, though no oribatid mites are parasitic.[11]

Many mites are parasitic on plants and animals. One family of mites Pyroglyphidae, or nest mites, live primarily in the nests of birds and animals. These mites are largely parasitic and consume blood, skin and keratin. Dust mites, which feed mostly on dead skin and hair shed from humans instead of consuming them from the organism directly, evolved from these parasitic ancestors.[12]

Insects are sometimes infested by parasitic mites. Examples are Varroa destructor, which attaches to the body of the honey bee, and Acarapis woodi (family Tarsonemidae), which lives in the tracheae of honey bees. Hundreds of species are associated with other bees, mostly poorly described. They attach to bees in a variety of ways. For example, Trigona corvina workers have been found with mites attached to the outer face of their hind tibiae.[13] Some are thought to be parasites, while others are beneficial symbionts. Mites also parasitize some ant species, such as Eciton burchellii.

Plant pests include the so-called spider mites (family Tetranychidae), thread-footed mites (family Tarsonemidae), and the gall mites (family Eriophyidae). Among the species that attack animals are members of the sarcoptic mange mites (family Sarcoptidae), which burrow under the skin. Demodex mites (family Demodicidae) are parasites that live in or near the hair follicles of mammals, including humans.

The tropical species Archegozetes longisetosus is one of the strongest animals in the world, relative to its mass (100 μg): It lifts up to 1,182 times its own weight, over five times more than would be expected of such a minute animal.[14] Mites also hold the record speed; for its length, Paratarsotomus macropalpis is the fastest animal on Earth.

Relationship with humansEdit

Mites are tiny, almost invisible, and apart from those that are of economic concern to humans, little studied. The majority are beneficial, living in the soil or aqueous environments and assisting in the decomposition of decaying organic material, or consuming fungi, plant or animal matter, as part of the carbon cycle.[8]

Medical significanceEdit

The majority of mite species are harmless to humans and domestic animals, but a few species can colonize mammals directly, acting as vectors for disease transmission, and causing or contributing to allergenic diseases.

Mites which colonize human skin are the cause of several types of itchy skin rashes, such as grain itch, grocer's itch, and scabies. Sarcoptes scabiei is a parasitic mite responsible for scabies which is one of the three most common skin disorders in children.[15] Demodex mites, which are common cause of mange in dogs and other domesticated animals, have also been implicated in the human skin disease rosacea, although the mechanism by which demodex contributes to the disease is unclear.

 
Public health worker Stefania Lanzia using a soft toy scabies mite to publicise scabies, an often overlooked condition especially among the elderly.

Chiggers are known primarily for their itchy bite, but they can also spread disease in some limited circumstances, such as scrub typhus. The house-mouse mite is the only known vector of the disease rickettsialpox.[16]

House dust mites, found in warm and humid places such as beds, cause several forms of allergic diseases, including hay fever, asthma and eczema, and are known to aggravate atopic dermatitis.[17]

Among domestic animals, sheep are affected by the mite Psoroptes ovis which lives on the skin, causing hypersensitivity and inflammation.[18]

In cultureEdit

Mites were first observed under the microscope by Robert Hooke. In his 1665 book Micrographia, he stated that far from being spontaneously generated from dirt, they were "very prettily shap'd Insects".[19] The world's first science documentary featured cheese mites, seen under the microscope; the short film was shown in London's Alhambra music hall in 1903, causing a boom in the sales of simple microscopes.[19] A few years later, Arthur Conan Doyle wrote a satirical poem, Parable, with the conceit of some cheese mites disputing the origin of the round Cheddar cheese in which they all lived.[19]

See alsoEdit

ReferencesEdit

Notes

  1. ^ Gerald W. Krantz; D. E. Walter, eds. (2009). A Manual of Acarology (3rd ed.). Texas Tech University Press. ISBN 978-0-89672-620-8. 
  2. ^ Walter, David Evans; Krantz, Gerald; Lindquist, Evert (13 December 1996). "Acari: The mites". Tree of Life Web Project. Retrieved 6 October 2017. 
  3. ^ Barker, S.C. & Murrell, A. (2004). "Systematics and evolution of ticks with a list of valid genus and species names". Parasitology. 129 (7): S15–S36. doi:10.1017/S0031182004005207. 
  4. ^ Sanggaard, Kristian W.; Bechsgaard, Jesper S.; Fang, Xiaodong (6 May 2014). "Spider genomes provide insight into composition and evolution of venom and silk". Nature Communications. 5: 3765. Bibcode:2014NatCo...5E3765S. doi:10.1038/ncomms4765. ISSN 2041-1723. PMC 4273655 . PMID 24801114. 
  5. ^ Dabert, Miroslawa; Witalinski, Wojciech; Kazmierski, Andrzej; Olszanowski, Ziemowit; Dabert, Jacek (2010). "Molecular phylogeny of acariform mites (Acari, Arachnida): Strong conflict between phylogenetic signal and long-branch attraction artifacts". Molecular Phylogenetics and Evolution. 56 (1): 222–241. doi:10.1016/j.ympev.2009.12.020. ISSN 1055-7903. 
  6. ^ a b c d e f g Ruppert, Edward E.; Fox, Richard, S.; Barnes, Robert D. (2004). Invertebrate Zoology, 7th edition. Cengage Learning. pp. 590–595. ISBN 978-81-315-0104-7. 
  7. ^ Balashov, Y.S. (1972). Bloodsucking Ticks - Vectors of Diseases of Man and Animals. Miscellaneous Publications of the Entomological Society of America, 8: 161–376.
  8. ^ a b Jeppson, L.R.; Keifer, Hartford H.; Baker, Edward William (1975). Mites Injurious to Economic Plants. University of California Press. pp. 1–3. ISBN 978-0-520-02381-9. 
  9. ^ R. B. Halliday, B. M. OConnor & A. S. Baker (2000). "Global Diversity of Mites". In Peter H. Raven; Tania Williams. Nature and human society: the quest for a sustainable world : proceedings of the 1997 Forum on Biodiversity. National Academies. pp. 192–212. 
  10. ^ a b Capinera, John L. (2008). Encyclopedia of Entomology. Springer Science & Business Media. p. 2425. ISBN 978-1-4020-6242-1. 
  11. ^ Arroyo, J.; Keith, A.M.; Schmidt, O.; Bolger, T. (2013). "Mite abundance and richness in an Irish survey of soil biodiversith with comments on some newly recorded species". Ir Nat. J. 33: 19–27. 
  12. ^ Erickson, Jim. "Genetic study of house dust mites demonstrates reversible evolution". Michigan News. Retrieved 31 May 2014. 
  13. ^ 1883-1960., Schwarz, Herbert Ferlando,; Louise., Bacon, Annette. "Stingless bees (Meliponidae) of the Western Hemisphere : Lestrimelitta and the following subgenera of Trigona : Trigona, Paratrigona, Schwarziana, Parapartamona, Cephalotrigona, Oxytrigona, Scaura, and Mourella. Bulletin of the AMNH ; v. 90". digitallibrary.amnh.org. Retrieved 2015-11-05. 
  14. ^ Michael Heethoff & Lars Koerner (2007). "Small but powerful – the oribatid mite Archegozetes longisetosus Aoki (Acari, Oribatida) produces disproportionate high forces". Journal of Experimental Biology. 210 (17): 3036–3042. doi:10.1242/jeb.008276. PMID 17704078. 
  15. ^ Andrews RM, McCarthy J, Carapetis JR, Currie BJ (December 2009). "Skin disorders, including pyoderma, scabies, and tinea infections". Pediatr. Clin. North Am. 56 (6): 1421–40. doi:10.1016/j.pcl.2009.09.002. PMID 19962029. 
  16. ^ Diaz, J. H. (2010). "Endemic mite-transmitted dermatoses and infectious diseases in the South". The Journal of the Louisiana State Medical Society : official organ of the Louisiana State Medical Society. 162 (3): 140–145, 147–149. PMID 20666166. 
  17. ^ Paul Klenerman; Brian Lipworth. "House dust mite allergy". NetDoctor. Retrieved February 20, 2008. 
  18. ^ Van den Broek, A. (2000). "Cutaneous and systemic responses during primary and challenge infestations of sheep with the sheep scab mite, Psoroptes ovis". Parasite Immunology. 22 (8): 407–414. doi:10.1046/j.1365-3024.2000.00318.x. 
  19. ^ a b c Marren, Peter; Mabey, Richard (2010). Bugs Britannica. Chatto & Windus. pp. 122–125. ISBN 978-0-7011-8180-2. 

External linksEdit