Acarina
Encyclopedia
Acari are a taxon
of arachnids that contains mite
s and tick
s. The diversity of the Acari is extraordinary and its fossil history goes back to at least the early Devonian
period. As a result, acarologists (the people who study mites and ticks) have proposed a complex set of taxonomic ranks to classify mites. In most modern treatments, the Acari is considered a subclass
of Arachnid
a and is composed of 2-3 superorders or order
s: Acariformes
(or Actinotrichida), Parasitiformes
(or Anactinotrichida), and Opilioacariformes
; the latter is often considered a subgroup within the Parasitiformes. The monophyly
of the Acari is open to debate, and the relationships of the acarines to other arachnids is not at all clear. In older treatments, the subgroups of the Acarina were placed at order rank, but as their own subdivisions have become better-understood, it is more usual to treat them at superorder rank.
Most acarines are minute to small (e.g. 0.08 millimetre), but the largest Acari (some ticks and red velvet mites) may reach lengths of 10–20 mm (0.393700787401575–0.78740157480315 ). It is estimated that over 50,000 species have been described (as of 1999) and that a million or more species are currently living. The study of mites and ticks is called acarology (from Greek
/, , a type of mite; and , -logia
), and the leading scientific journal
s for acarology include Acarologia, Experimental and Applied Acarology and the International Journal of Acarology
.
s and, as such, should have a segmented body with the segments organised into two tagmata
: a prosoma (cephalothorax) and an opisthosoma
(abdomen). However, only the faintest traces of primary segmentation remain in mites; the prosoma and opisthosoma are insensibly fused, and a region of flexible cuticle (the cirumcapitular furrow) separates the chelicerae and pedipalps from the rest of the body. This anterior body region is called the capitulum or gnathosoma
and, according to some workers, is also found in Ricinulei
. The remainder of the body is called the idiosoma and is unique to mites.
Most adult mites have four pairs of legs, like other arachnids, but some have fewer. For example, gall mites like Phyllocoptes variabilis (family Eriophyidae) have a worm-like body with only two pairs of legs; some parasitic mites have only one or three pairs of legs in the adult stage. Larval and prelarval stages have a maximum of three pairs of legs; adult mites with only three pairs of legs may be called 'larviform'.
The mouth parts of mites may be adapted for biting, stinging, sawing or sucking. They breathe through trachea
e, stigmata (small openings of the skin), intestines and the skin itself. Species hunting for other mites have very acute senses, but many mites are eyeless. The central eyes of arachnids are always missing, or they are fused into a single eye. Thus, any eye number from none to five may occur.
typically consists of an egg, a prelarval stage (often absent), a larval stage (hexapod except in Eriophyoidea which have only two pairs of legs), and a series of nymphal stages. Any or all of these stages except the adult may be suppressed or occur only within the body of a previous stage. Larvae (and prelarvae) have a maximum of three pairs of legs (legs are often reduced to stubs or absent in prelarvae); legs IV are added at the first nymphal stage. Usually a maximum of three nymphal stages are present and they are referred to in sequence as protonymph, deutonymph, and tritonymph; however, some soft ticks have supernumerary nymphal stages. The females of some Tarsonemidae
bear sexually mature young. If one or more nymphal stages are absent, then authors may disagree on which stages are present. Only the Oribatida
pass through all developmental stages.
s in the soil organic matter and detritus
. Many are parasitic
, and they affect both vertebrate
s and invertebrate
s. Most parasitic forms are external parasites, while the free living forms are generally predatory
and may even be used to control undesirable arthropods. Others are detritivore
s that help to break down forest litter
and dead organic matter such as skin
cells. Others still are plant feeders and may damage crops
.
s and their relatives (Tetranychoidea), earth mites (Penthaleidae
), thread-footed mites (Tarsonemidae
) and the gall and rust mites (Eriophyidae).
Some parasitic forms affect human
s and other mammal
s, causing damage by their feeding, and can even be vectors of diseases
such as scrub typhus
, rickettsialpox
, Lyme disease
, Q fever
, Colorado tick fever
, tularemia
, tick-borne relapsing fever
, babesiosis
, ehrlichiosis
and tick-borne meningoencephalitis
. A well known effect of mites on humans is their role as an allergen
and the stimulation of asthma
in people affected by respiratory disease
.
The use of predatory mites (e.g. Phytoseiidae
) in pest control
and herbivorous mites that infest weeds are also of importance. An unquantified, but major positive contribution of the Acari is their normal functioning in ecosystems, especially their roles in the decomposer subsystem.
Chemical agents used to control ticks and mites include dusting sulfur
and ivermectin.
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The phylogeny of the Acari is still disputed and several taxonomic schemes have been proposed for their classification. The third edition of the standard textbook A Manual of Acarology uses a system of six orders
, grouped into two superorders:
}\
Taxon
|thumb|270px|[[African elephants]] form a widely-accepted taxon, the [[genus]] LoxodontaA taxon is a group of organisms, which a taxonomist adjudges to be a unit. Usually a taxon is given a name and a rank, although neither is a requirement...
of arachnids that contains mite
Mite
Mites, along with ticks, are small arthropods belonging to the subclass Acari and the class Arachnida. The scientific discipline devoted to the study of ticks and mites is called acarology.-Diversity and systematics:...
s and tick
Tick
Ticks are small arachnids in the order Ixodida, along with mites, constitute the subclass Acarina. Ticks are ectoparasites , living by hematophagy on the blood of mammals, birds, and sometimes reptiles and amphibians...
s. The diversity of the Acari is extraordinary and its fossil history goes back to at least the early Devonian
Devonian
The Devonian is a geologic period and system of the Paleozoic Era spanning from the end of the Silurian Period, about 416.0 ± 2.8 Mya , to the beginning of the Carboniferous Period, about 359.2 ± 2.5 Mya...
period. As a result, acarologists (the people who study mites and ticks) have proposed a complex set of taxonomic ranks to classify mites. In most modern treatments, the Acari is considered a subclass
Class (biology)
In biological classification, class is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, order, family, genus, and species, with class fitting between phylum and order...
of Arachnid
Arachnid
Arachnids are a class of joint-legged invertebrate animals in the subphylum Chelicerata. All arachnids have eight legs, although in some species the front pair may convert to a sensory function. The term is derived from the Greek words , meaning "spider".Almost all extant arachnids are terrestrial...
a and is composed of 2-3 superorders or order
Order (biology)
In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...
s: Acariformes
Acariformes
The Acariformes are the more diverse of the two superorders of mites. There are over 32,000 described species in 351 families, and an estimated total of 440,000 to 929,000, including undescribed species.-Systematics and taxonomy:...
(or Actinotrichida), Parasitiformes
Parasitiformes
The Parasitiformes are a superorder of Acari . Many species are parasitic , but not all; for example, about half of the 10,000 known species in the suborder Mesostigmata are predatory and cryptozoan, living in the soil-litter, rotting wood, dung, carrion, nests or house dust...
(or Anactinotrichida), and Opilioacariformes
Opilioacariformes
Opilioacariformes is the smallest order of mites, containing a single family, and around 10 genera. They are rare, large mites, and are widely considered primitive, as they retain six pairs of eyes, and abdominal segmentation...
; the latter is often considered a subgroup within the Parasitiformes. The monophyly
Monophyly
In common cladistic usage, a monophyletic group is a taxon which forms a clade, meaning that it contains all the descendants of the possibly hypothetical closest common ancestor of the members of the group. The term is synonymous with the uncommon term holophyly...
of the Acari is open to debate, and the relationships of the acarines to other arachnids is not at all clear. In older treatments, the subgroups of the Acarina were placed at order rank, but as their own subdivisions have become better-understood, it is more usual to treat them at superorder rank.
Most acarines are minute to small (e.g. 0.08 millimetre), but the largest Acari (some ticks and red velvet mites) may reach lengths of 10–20 mm (0.393700787401575–0.78740157480315 ). It is estimated that over 50,000 species have been described (as of 1999) and that a million or more species are currently living. The study of mites and ticks is called acarology (from Greek
Ancient Greek
Ancient Greek is the stage of the Greek language in the periods spanning the times c. 9th–6th centuries BC, , c. 5th–4th centuries BC , and the c. 3rd century BC – 6th century AD of ancient Greece and the ancient world; being predated in the 2nd millennium BC by Mycenaean Greek...
/, , a type of mite; and , -logia
-logy
-logy is a suffix in the English language, used with words originally adapted from Ancient Greek language ending in -λογία...
), and the leading scientific journal
Scientific journal
In academic publishing, a scientific journal is a periodical publication intended to further the progress of science, usually by reporting new research. There are thousands of scientific journals in publication, and many more have been published at various points in the past...
s for acarology include Acarologia, Experimental and Applied Acarology and the International Journal of Acarology
International Journal of Acarology
The International Journal of Acarology is a peer-reviewed scientific journal of agricultural, aquatic, general, medical, and veterinary acarology. Topics covered include mite and tick behavior, biochemistry, biology, biological pest control, ecology, evolution, morphology, physiology, systematics,...
.
Morphology
Mites are arachnidArachnid
Arachnids are a class of joint-legged invertebrate animals in the subphylum Chelicerata. All arachnids have eight legs, although in some species the front pair may convert to a sensory function. The term is derived from the Greek words , meaning "spider".Almost all extant arachnids are terrestrial...
s and, as such, should have a segmented body with the segments organised into two tagmata
Tagma (biology)
In invertebrate biology, a tagma is a specialized grouping of arthropod segments, such as the head, the thorax, and the abdomen with a common function. The segments of a tagma may be either fused or moveable.-Tagmata:...
: a prosoma (cephalothorax) and an opisthosoma
Opisthosoma
The opisthosoma is the posterior part of the body in some arthropods, behind the prosoma . It is a distinctive feature of the subphylum Chelicerata...
(abdomen). However, only the faintest traces of primary segmentation remain in mites; the prosoma and opisthosoma are insensibly fused, and a region of flexible cuticle (the cirumcapitular furrow) separates the chelicerae and pedipalps from the rest of the body. This anterior body region is called the capitulum or gnathosoma
Gnathosoma
The gnathosoma is the part of the body of the Acari comprising the mouth and feeding parts. These are the hypostome, the chelicerae and the pedipalps. It is also called the capitulum...
and, according to some workers, is also found in Ricinulei
Ricinulei
The Order Ricinulei is a group of arachnids known as hooded tickspiders. In older works they are sometimes referred to as Podogona., 60 extant species of ricinuleids have been described worldwide, all in the single family Ricinoididae. They occur today in west-central Africa and the Neotropical...
. The remainder of the body is called the idiosoma and is unique to mites.
Most adult mites have four pairs of legs, like other arachnids, but some have fewer. For example, gall mites like Phyllocoptes variabilis (family Eriophyidae) have a worm-like body with only two pairs of legs; some parasitic mites have only one or three pairs of legs in the adult stage. Larval and prelarval stages have a maximum of three pairs of legs; adult mites with only three pairs of legs may be called 'larviform'.
The mouth parts of mites may be adapted for biting, stinging, sawing or sucking. They breathe through trachea
Invertebrate trachea
The invertebrate trachea refers to the open respiratory system composed of spiracles, tracheae, and tracheoles that terrestrial arthropods have to transport metabolic gases to and from tissues....
e, stigmata (small openings of the skin), intestines and the skin itself. Species hunting for other mites have very acute senses, but many mites are eyeless. The central eyes of arachnids are always missing, or they are fused into a single eye. Thus, any eye number from none to five may occur.
Ontogeny
Acarine ontogenyOntogeny
Ontogeny is the origin and the development of an organism – for example: from the fertilized egg to mature form. It covers in essence, the study of an organism's lifespan...
typically consists of an egg, a prelarval stage (often absent), a larval stage (hexapod except in Eriophyoidea which have only two pairs of legs), and a series of nymphal stages. Any or all of these stages except the adult may be suppressed or occur only within the body of a previous stage. Larvae (and prelarvae) have a maximum of three pairs of legs (legs are often reduced to stubs or absent in prelarvae); legs IV are added at the first nymphal stage. Usually a maximum of three nymphal stages are present and they are referred to in sequence as protonymph, deutonymph, and tritonymph; however, some soft ticks have supernumerary nymphal stages. The females of some Tarsonemidae
Tarsonemidae
Tarsonemidae is a family of mites, also called thread-footed mites or white mites.Only a limited number of tarsonemid genera are known to feed on higher plants while most species in this family feed on the thin-walled mycelia of fungi or possibly algal bodies...
bear sexually mature young. If one or more nymphal stages are absent, then authors may disagree on which stages are present. Only the Oribatida
Oribatida
Oribatida , also known as moss mites or beetle mites, are an order of mites, in the "chewing Acariformes" clade Sarcoptiformes. They range in size from ....
pass through all developmental stages.
Diversity and lifestyles
Acarines are extremely diverse. They live in practically every habitat, and include aquatic (freshwater and sea water) and terrestrial species. They outnumber other arthropodArthropod
An arthropod is an invertebrate animal having an exoskeleton , a segmented body, and jointed appendages. Arthropods are members of the phylum Arthropoda , and include the insects, arachnids, crustaceans, and others...
s in the soil organic matter and detritus
Detritus (biology)
In biology, detritus is non-living particulate organic material . It typically includes the bodies or fragments of dead organisms as well as fecal material. Detritus is typically colonized by communities of microorganisms which act to decompose the material...
. Many are parasitic
Parasitism
Parasitism is a type of symbiotic relationship between organisms of different species where one organism, the parasite, benefits at the expense of the other, the host. Traditionally parasite referred to organisms with lifestages that needed more than one host . These are now called macroparasites...
, and they affect both vertebrate
Vertebrate
Vertebrates are animals that are members of the subphylum Vertebrata . Vertebrates are the largest group of chordates, with currently about 58,000 species described. Vertebrates include the jawless fishes, bony fishes, sharks and rays, amphibians, reptiles, mammals, and birds...
s and invertebrate
Invertebrate
An invertebrate is an animal without a backbone. The group includes 97% of all animal species – all animals except those in the chordate subphylum Vertebrata .Invertebrates form a paraphyletic group...
s. Most parasitic forms are external parasites, while the free living forms are generally predatory
Predation
In ecology, predation describes a biological interaction where a predator feeds on its prey . Predators may or may not kill their prey prior to feeding on them, but the act of predation always results in the death of its prey and the eventual absorption of the prey's tissue through consumption...
and may even be used to control undesirable arthropods. Others are detritivore
Detritivore
Detritivores, also known as detritophages or detritus feeders or detritus eaters or saprophages, are heterotrophs that obtain nutrients by consuming detritus . By doing so, they contribute to decomposition and the nutrient cycles...
s that help to break down forest litter
Plant litter
Plant litter, leaf litter or tree litter is dead plant material, such as leaves, bark, needles, and twigs, that has fallen to the ground. Litter provides habitat for small animals, fungi, and plants, and the material may be used to construct nests. As litter decomposes, nutrients are released to...
and dead organic matter such as skin
Skin
-Dermis:The dermis is the layer of skin beneath the epidermis that consists of connective tissue and cushions the body from stress and strain. The dermis is tightly connected to the epidermis by a basement membrane. It also harbors many Mechanoreceptors that provide the sense of touch and heat...
cells. Others still are plant feeders and may damage crops
Crop (agriculture)
A crop is a non-animal species or variety that is grown to be harvested as food, livestock fodder, fuel or for any other economic purpose. Major world crops include maize , wheat, rice, soybeans, hay, potatoes and cotton. While the term "crop" most commonly refers to plants, it can also include...
.
Economic importance
Damage to crops is perhaps the most costly economic effect of mites, especially by the spider miteSpider mite
Spider mites are members of the Acari family Tetranychidae, which includes about 1,200 species. They generally live on the under sides of leaves of plants, where they may spin protective silk webs, and they can cause damage by puncturing the plant cells to feed...
s and their relatives (Tetranychoidea), earth mites (Penthaleidae
Penthaleidae
Penthaleidae, also referred to as earth mites, are a family of mites that are major winter pests of a variety of crops and pastures in southern Australia....
), thread-footed mites (Tarsonemidae
Tarsonemidae
Tarsonemidae is a family of mites, also called thread-footed mites or white mites.Only a limited number of tarsonemid genera are known to feed on higher plants while most species in this family feed on the thin-walled mycelia of fungi or possibly algal bodies...
) and the gall and rust mites (Eriophyidae).
Some parasitic forms affect human
Human
Humans are the only living species in the Homo genus...
s and other mammal
Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...
s, causing damage by their feeding, and can even be vectors of diseases
Tick-borne disease
Tick-borne diseases are diseases or illnesses transmitted by ticks. As the incidence of tick-borne illnesses increases and the geographic areas in which they are found expand, it becomes increasingly important that health professionals be able to distinguish the diverse, and often overlapping,...
such as scrub typhus
Scrub typhus
Scrub typhus or Bush typhus is a form of typhus caused by Orientia tsutsugamushi first isolated and identified in 1930 in Japan., accessdate: 16 October 2011...
, rickettsialpox
Rickettsialpox
Rickettsialpox is an illness caused by bacteria of the Rickettsia genus . Physician Robert Huebner and self-trained entomologist Charles Pomerantz played major roles in identifying the etiology of the disease after an outbreak in 1946 in a New York City apartment complex, documented in medical...
, Lyme disease
Lyme disease
Lyme disease, or Lyme borreliosis, is an emerging infectious disease caused by at least three species of bacteria belonging to the genus Borrelia. Borrelia burgdorferi sensu stricto is the main cause of Lyme disease in the United States, whereas Borrelia afzelii and Borrelia garinii cause most...
, Q fever
Q fever
Q fever is a disease caused by infection with Coxiella burnetii, a bacterium that affects humans and other animals. This organism is uncommon but may be found in cattle, sheep, goats and other domestic mammals, including cats and dogs...
, Colorado tick fever
Colorado tick fever
Colorado Tick Fever is an obtuse viral infection transmitted from the bite of an infected tick...
, tularemia
Tularemia
Tularemia is a serious infectious disease caused by the bacterium Francisella tularensis. A Gram-negative, nonmotile coccobacillus, the bacterium has several subspecies with varying degrees of virulence. The most important of those is F...
, tick-borne relapsing fever
Relapsing fever
Relapsing fever is an infection caused by certain bacteria in the genus Borrelia. It is a vector-borne disease that is transmitted through the bites of lice or soft-bodied ticks.-Louse-borne relapsing fever:...
, babesiosis
Babesiosis
Babesiosis is a malaria-like parasitic disease caused by infection with Babesia, a genus of protozoal piroplasms. After trypanosomes, Babesia are thought to be the second most common blood parasites of mammals and they can have a major impact on health of domestic animals in areas without severe...
, ehrlichiosis
Ehrlichiosis
Ehrlichiosis is a tick-borne disease of dogs usually caused by the organism Ehrlichia canis. Ehrlichia canis is the pathogen of animals. Humans can become infected by E. canis and other species after tick exposure. German Shepherd dogs are thought to be particularly affected by the disease, other...
and tick-borne meningoencephalitis
Tick-borne meningoencephalitis
Tick-borne encephalitis is a viral infectious disease involving the central nervous system. The disease most often manifests as meningitis, encephalitis, or meningoencephalitis. Although TBE is most commonly recognized as a neurological disorder, mild fever can also occur...
. A well known effect of mites on humans is their role as an allergen
Allergen
An allergen is any substance that can cause an allergy. In technical terms, an allergen is a non-parasitic antigen capable of stimulating a type-I hypersensitivity reaction in atopic individuals....
and the stimulation of asthma
Asthma
Asthma is the common chronic inflammatory disease of the airways characterized by variable and recurring symptoms, reversible airflow obstruction, and bronchospasm. Symptoms include wheezing, coughing, chest tightness, and shortness of breath...
in people affected by respiratory disease
Respiratory disease
Respiratory disease is a medical term that encompasses pathological conditions affecting the organs and tissues that make gas exchange possible in higher organisms, and includes conditions of the upper respiratory tract, trachea, bronchi, bronchioles, alveoli, pleura and pleural cavity, and the...
.
The use of predatory mites (e.g. Phytoseiidae
Phytoseiidae
Phytoseiidae is a family of mites which feed on thrips and other mite species. They are often used as a biological control agent for managing mite pests.-Subfamilies:* Amblyseiinae Muma, 1961* Phytoseiinae Berlese, 1916* Typhlodrominae Scheuten, 1857...
) in pest control
Pest control
Pest control refers to the regulation or management of a species defined as a pest, usually because it is perceived to be detrimental to a person's health, the ecology or the economy.-History:...
and herbivorous mites that infest weeds are also of importance. An unquantified, but major positive contribution of the Acari is their normal functioning in ecosystems, especially their roles in the decomposer subsystem.
Chemical agents used to control ticks and mites include dusting sulfur
Sulfur
Sulfur or sulphur is the chemical element with atomic number 16. In the periodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow...
and ivermectin.
Taxonomy
Order (biology)
In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...
, grouped into two superorders:
- Superorder ParasitiformesParasitiformesThe Parasitiformes are a superorder of Acari . Many species are parasitic , but not all; for example, about half of the 10,000 known species in the suborder Mesostigmata are predatory and cryptozoan, living in the soil-litter, rotting wood, dung, carrion, nests or house dust...
– ticks and a variety of mites.- Opilioacarida – mites that superficially resemble harvestmen (OpilionesOpilionesOpiliones are an order of arachnids commonly known as harvestmen. , over 6,400 species of harvestmen have been discovered worldwide, although the real number of extant species may exceed 10,000. The order Opiliones can be divided into four suborders: Cyphophthalmi, Eupnoi, Dyspnoi and Laniatores...
, hence their name) - HolothyridaHolothyridaThe Holothyrida are a small order of mites in the superorder Parasitiformes. No fossils are known. With body lengths of more than 2 mm they are relatively large mites, with a heavily sclerotized body. They mainly feed on the body fluids of dead arthropods...
- Ixodida – hard and soft ticks
- MesostigmataMesostigmataMesostigmata is an order of mites belonging to the Parasitiformes. Unlike most members of that group, many of these mites are not parasitic but free-living and predatory. They can be recognized by the single pair of spiracles positioned laterally on the body....
– bird mites, phytoseiid mites, Raubmilben- Sejoidea
- Trigynaspida
- Monogynaspida
- Opilioacarida – mites that superficially resemble harvestmen (Opiliones
- Superorder AcariformesAcariformesThe Acariformes are the more diverse of the two superorders of mites. There are over 32,000 described species in 351 families, and an estimated total of 440,000 to 929,000, including undescribed species.-Systematics and taxonomy:...
– the most diverse group of mites.- TrombidiformesTrombidiformesThe Trombidiformes is a large, diverse order of mites, comprising around 125 families and more than 22,000 described species. The group has few synapomorphies by which it can be defined, unlike the other major group of acariform mites, Sarcoptiformes...
– 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.- Sphaerolichida
- ProstigmataProstigmataThe Prostigmata is a suborder of mites belonging to the Trombidiformes, which contain the "sucking" members of the "true mites" ....
- SarcoptiformesSarcoptiformesSarcoptiformes is an order of Acari....
- Endeostigmata – basal sarcoptiform lineages
- OribatidaOribatidaOribatida , also known as moss mites or beetle mites, are an order of mites, in the "chewing Acariformes" clade Sarcoptiformes. They range in size from ....
– oribatid mites, beetle mites, armored mites (also cryptostigmata) - AstigmataAstigmataThe Astigmatina are a "cohort" of mites. They belong to the Sarcoptiformes, which contain the "biting" Acariformes. Many species are parasites of vertebrates. Most notorious among these are the Psoroptidia, which contain such notable taxa as feather mites and Sarcoptes scabiei.The Astigmata are of...
– stored product, fur, feather, dust, and human itch mites, etc.
- Trombidiformes
Further reading
- Experimental and Applied Acarology, ISSN: 1572-9702 (electronic) 0168-8162 (paper), Springer
External links
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