Mesostigmata is an order of mites belonging to the Parasitiformes. They are by far the largest group of Parasitiformes, with over 8,000 species in 130 families. Mesostigmata includes parasitic as well as free-living and predatory forms. They can be recognized by the single pair of spiracles positioned laterally on the body.
Amongst the best known species are Varroa destructor, an economically important parasite of honey bees, as well as the red mite (Dermanyssus gallinae), a parasite of poultry, most commonly chickens.
Description
Mesostigmata are mites ranging from 0.12–4 mm long (0.2–4 mm according to another source[2]). They have a pair of stigmatal openings above legs III-IV usually associated with a peritrematal groove. The gnathosoma has a sclerotised ring around the bases of the chelicerae (basis capitulum). The palps have 5 (rarely 4) free segments and usually a subdistal palp apotele. The chelicerae are 3-segmented. The subcapitulum usually has a median groove with transverse rows of 1-many denticles. There are usually bifurcate or membranous corniculi present. Except in some parasitic species, a flagellate tritosternum is present. The coxae of the legs are freely articulating with the body. The intercoxal region has sternal and genital shield elements. Adults have a genital opening and either chelicerae modified for sperm transfer (if male) or a sperm-receiving structure (if female).[3]
The above description applies to adults. Larvae have six legs, instead of the eight possessed by later stages, and may or may not feed. There are two nymphal stages (protonymph, deutonymph) that usually have lightly sclerotized dorsal, intercoxal and ventral plates.[3]
Ecology
Many Mesostigmata are free-living predators of invertebrates that live in soil and litter, on the soil surface or on plants.[4] There are also some that live in freshwater.[5] Other Mesostigmata are parasites of vertebrates or arthropods, pollen and nectar feeders in flowers, fungus feeders, or saprophages that subsist on dead or decaying organic matter.[2][3]
The soil-dwelling Mesostigmata are not as abundant as oribatids or prostigmatids that also occur in this habitat, but they are still ubiquitous in soil and may be important predators. Larger species tend to be predators of small arthropods or arthropod eggs, whereas smaller species prey on nematodes. Size of these mesostigmatans decreases with soil depth: plant litter and humus have large species such as Veigaia (Veigaiidae), the humus-soil interface has smaller species like Dendrolaelaps (Digamasellidae) and the mineral soil has the tiny Rhodacarellus (Rhodacaridae).[6]
A few species are known from freshwater habitats, such as wet soil, phytotelmata, waterside vegetation and sewage filter-beds. These appear to move by crawling as no species are known to swim. Some species are known to prey on mosquito eggs and one species was reared on a diet of nematodes.[5]
The parasitic Mesostigmata are mostly in superfamily Dermanyssoidea. These include parasites of invertebrates (e.g. Varroidae) and of vertebrates (other families), as well as both ectoparasites (external) and endoparasites (internal).[7]
Phoresy, the temporary attachment of a smaller animal to a larger one for travel, is common in the Mesostigmata. For example, the freshwater species are phoretic on flies of families Tipulidae, Ceratopogonidae, and Culicidae.[5]
Economic importance
Varroa destructor (Varroidae) is a major pest of honey bees. It harms bees both directly by feeding on fat body tissue, and indirectly by transmitting viruses.[8]
In agriculture, soil-dwelling mesostigmatans are important predators of nematodes, springtails and insect larvae, while plant-dwelling mesostigmatans control pests such as spider mites.[4]
Evolution
The oldest known record of the group is an indeterminate Sejidae deutonymph from the mid-Cretaceous (Albian-Cenomanian) aged Burmese amber of Myanmar.[10]
Taxonomy
Taxonomy to families (Beaulieu 2011). Genus and species counts fluctuate over time.[1][11]
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