INVERTEBRATE ZOOLOGY IN THREE VOLUMES - BOOK 2 - H.Y. Shcherbak - 1996

PHYLUM ARTHROPODA

SUBPHYLUM CHELICERATA

CLASS ARACHNIDA

SUBCLASS ACARINA (MITES AND TICKS)

Mites and ticks are among the most widespread animal groups on Earth, found on all continents, including Antarctica. The majority are free-living organisms inhabiting soils, leaf litter, and various Other forms of decaying organic matter. For instance, in eastern Canada, as many as one million mites belonging to 100 species from 50 families can be found in a single square meter (1 m²) of forest litter. Some species inhabit various freshwater bodies, as well as seas and oceans.

Among free-living mites, predators and saprophages are common, alongside necrophages and facultative hematophages. Research on free-living mites is still in its infancy, whereas parasitic species have been studied in much greater detail. These parasites inhabit the feathers of birds, as well as the integument, and the respiratory, digestive, and reproductive systems of numerous vertebrates, including humans.

Mites and ticks are well known as vectors of pathogens causing various infectious diseases in domestic and wild animals and humans, as well as triggers of allergic asthma in people. Many species are parasites of higher plants, and they are also found in all Fungi, Lichens, and mosses.

lichen, and mosses.

Most mites are microscopic organisms with a body length of up to 1 mm, rarely reaching 2.5–7 mm, and only ixodid ticks expand to 25–30 mm after a Blood meal. According to specialists, this miniaturization was the key aromorphosis that drove the biological success of these animals. About 50,000 species have been described, which represents only a fraction of those existing in nature. In Ukraine, The Study of mites began only in recent decades, with approximately 3,000 species discovered to date.

Mites are readily distinguished from other arachnids by a combination of specific features: their mouthparts—including chelicerae and pedipalps—are separated from the trunk into a so-called false HEAD known as the gnathosoma, while body segmentation is indistinct or entirely lost. Segmented mites are unknown to science, and the exact number of segments comprising their body remains uncertain. Researchers infer segmentation from the arrangement of setae, dermal glands, and various grooves; however, there is no direct evidence confirming the primary nature of this layout. In the larval stage, mites typically possess three pairs of legs, whereas nymphal and adult stages have four pairs.

The body shape of mites is remarkably diverse: oval, egg-shaped, less commonly spherical, pear-shaped, or nearly triangular. In some forms, the body is worm-like. The gnathosoma is usually located anterior to the trunk (the idiosoma) and connected to it by a flexible, elastic membrane. In certain mites, the gnathosoma is shifted to the ventral side and occasionally concealed within a specialized cavity called the camerostome. The Fine Structure of the chelicerae and pedipalps varies greatly depending on their lifestyle.

As a rule, the legs of mites consist of seven segments. Primarily serving for locomotion, the first pair of legs in some groups loses its locomotor function and becomes specialized as a sensory organ. In Water mites, the legs are adapted for swimming. Many parasitic groups possess numerous specialized adaptations on their legs for clinging to bird feathers, mammalian fur, and the like. Males frequently bear stout cuticular outgrowths (apophyses) or modified setae on their legs, which they use to grasp females during copulation. Mites are also frequently brightly colored.

The smallest mites respire through their entire body surface, while larger forms possess a tracheal system that opens externally mainly via a single pair—or, much less frequently, two or four pairs—of spiracles or pore fields.

Fertilization is typically spermatophoric, although in some mite groups, the male deposits a droplet of seminal fluid that the following female takes up using her genital cone. In many species, only a single egg develops at a time, and females produce a relatively small number of eggs throughout their lifespan.

Parthenogenesis is quite common among mites, including arrhenotokous parthenogenesis (where unfertilized eggs develop exclusively into males), thelytoky (exclusively into females), and amphitoky (yielding both males and females).

The life cycle of mites most fully encompasses the following stages: egg, prelarva, larva, protonymph, deutonymph, and tritonymph. The prelarval stage occurs within the egg, where it molts to form an embryonic cuticle. As noted earlier, unlike the nymphal and adult stages, the larva possesses only three pairs of legs. Quite frequently, the life cycle is simplified and includes only one or two nymphal stages.

All mites are divided into three major groups: Opilioacarina, Parasitiformes, and Acariformes.

Opilioacarids are a small group (comprising 12 known species) of thermophilic, free-living, nocturnal predators that feed on small soil-dwelling animals and may also consume plant pollen and fungal spores.

Among the Parasitiformes (Fig. 204), ixodid ticks are the most thoroughly studied. They are temporary ectoparasites of vertebrates and humans, as well as specific vectors of pathogens causing numerous viral and bacterial zoonotic diseases. Ixodid ticks are distributed across all continents except Antarctica. About 700 species have been described, including 30 in the fauna of Ukraine.

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Fig. 204. Parasitiform mites:

a - Ixodes persulcatus in a questing posture; b - Allodermanyssus sanguineus; c - Varroa jacobsoni

All of them are hematophagous. Upon encountering a host, a tick slices the Skin with the movable digit of its chelicerae and inserts the gnathosoma into the wound, while the pedipalps deflect outward at a right angle to the gnathosoma. The ventral surface of the gnathosoma bears numerous recurved hooks that anchor the tick securely in the skin, acting much like miniature anchors. Simultaneously, salivary gland secretions are injected into the wound, which rapidly solidify to form a so-called cement sheath around the gnathosoma. The blood-feeding process lasts for many days; the tick ingests a massive volume

of blood that exceeds the weight and volume of a starved tick by tens or even hundreds of times. As a rule, a mite feeds only once during each developmental stage. Pathogens undergo part of their life cycle within the ticks and are transmitted transstadially and transovarially. The Life Cycle of ixodid ticks includes only a single nymphal stage.

The most well-known vectors of tick-borne encephalitis pathogens are the taiga tick (Ixodes persulcatus), common in the forests of the Russian taiga zone (Fig. 204, a), and the castor bean tick (Ixodes ricinus), which inhabits Europe and North Africa (see Fig. 189, e). The former species transmits the eastern variant of the virus, which causes so-called spring-summer encephalitis—a very severe and often fatal human disease. The latter species transmits the western variant of the virus, which causes a somewhat milder form of encephalitis.

Ixodid ticks are also involved in transmitting pathogens of other human diseases, such as Mediterranean spotted fever (vector Rhipicephalus sanguineus), common in the Mediterranean region, rocky mountain spotted fever in the Americas (vector Dermacentor andersoni), and many others. Ixodid ticks also cause significant damage to animal husbandry. Massive tick infestations exhaust animals and sometimes lead to paralysis (when parasitized by ticks of the genus Haemaphysalis). Furthermore, they act as vectors for pathogens of numerous animal diseases (such as piroplasmosis, nutalliosis, and brucellosis).

In countries with dry and warm climates, soft ticks of the family Argasidae are widespread (about 100 species have been described, with 9 found in Ukraine). These are specific vectors of spirochetosis pathogens, or tick-borne relapsing fevers (particularly species of the genus Ornithodoros).

There are known cases of humans being attacked by ticks of the genus Argas, which live as synanthropes in pigeon nests in attics, old adobe buildings, and similar locations.

Parasitiform mites include a large group known as gamasid mites. Around 5,000 species have been described; most of them are free-living predators or, like Opilioacarida, polyphages, though parasitic species also exist, including obligatory blood-feeders (i.e., those feeding exclusively on blood).

The poultry red mite (Dermanyssus gallinae) is widely known. City dwellers often encounter them in their homes, where the mites crawl in from pigeon nests, especially abandoned ones. Bites from these mites can cause acute dermatitis. Of greater danger to humans is the tropical rat mite Allodermanyssus sanguineus (Fig. 204, b), which is a specific vector of the pathogen causing rickettsialpox—a human disease that also occurs in Ukraine.

Infamous for its destructive impact is the varroa mite (Varroa jacobsoni, Fig. 204, c), which in the 1970s began to spread rapidly across Ukraine, causing immense losses to beekeeping. These mites feed on the hemolymph of pupae and adult bees. The number of parasites in a bee colony can reach 15,000 to 30,000 or more.

At the same time, predatory phytoseiid mites of the family Phytoseiidae have come into widespread use in the biological control of agricultural crop pests, particularly in greenhouses.

Acariform mites (Fig. 205) constitute the largest group in terms of species diversity. They inhabit both terrestrial environments as well as marine and freshwaters. Among them are free-living forms, including serious pests of stored agricultural products, as well as parasites of plants, animals, and humans. However, few act as vectors of infectious diseases; notably, chigger mites (family Trombiculidae) transmit the pathogen of Japanese river fever (tsutsugamushi disease) to humans (Fig. 205, a).

Fig. 205. Acariform mites

Among free-living acariform mites, oribatid mites (Oribatei) (Fig. 205, b) have been studied most thoroughly. They predominantly inhabit soil and leaf litter, where their density can exceed one million individuals per 1 m². They are also found on trees, in moss, lichens, rodent burrows, bird nests, and similar habitats. Ticks have occasionally been recorded in human dwellings. Oribatid mites are saprophages, phytophages, and mycophages. They play an important role in humification and the biogeochemical cycling of elements in soils, helping maintain soil porosity partly by creating burrow channels and partly by consuming decaying ROOT systems.

Grain or forage mites (Acaroidea) have long been known as pests that damage grain reserves in elevators and warehouses. At a humidity exceeding 17%, mass reproduction of these mites begins; they damage the germ in grains, contaminate the grain with molting skins, and so on. The most well-known grain pest is the flour mite (Acarus siro). In addition to grain, these mites infest other food stores, such as dried fruits and hard cheeses, and can multiply On the surface of wine. These mites are also pathogenic to humans; ingesting them with food can cause acute gastrointestinal disorders. Recently, these mites have been increasingly cited as agents of various allergic conditions, primarily atypical forms of Bronchial Asthma. The allergen has been isolated from several mite species, but its primary source was found to be the house dust mite (Dermatophagoides pteronyssinus). The allergic effect on human respiratory tracts is caused not so much by live mites as by their integuments. Mattresses and pillows are the primary habitats of these mites (hence their name), where they multiply rapidly. D. pteronyssinus feed exclusively on shed human epidermal scales. Dead mites accumulate in household dust.

Among endoparasitic astigmatid mites, the itch mite (Sarcoptes scabiei), which parasitizes the deeper layers of the epidermis and causes human Scabies, deserves primary mention (Fig. 205, c). A characteristic symptom of this condition is excruciating itching, associated with the highly allergenic secretions produced by the mites. Many species of itch mites also parasitize the skin of most domestic and many wild animals.

Ectoparasitic astigmatid mites are represented by highly specialized feather mites, which live on feathers, inside feather shafts, and on the skin of birds across all modern orders (with the exception of penguins), as well as fur mites that inhabit The coat of mammals, particularly rodents.

Most feather mites do not harm birds, feeding instead on the keratin parts of feathers, dead epidermal scales, avian Lymph, and the hemolymph of louse flies and chewing lice. However, certain species—such as the scaly leg mite (Knemidocoptes mutans), which lives beneath the scales on the featherless PARTS OF THE legs of chickens and other domestic fowl—cause a condition known as "scaly leg". The legs become covered with whitish, bumpy crusts beneath which tissue necrosis (death) occurs, potentially leading to the bird's death.

Serious plant pests include minute, worm-like mites that possess only two pairs of legs across all developmental stages. These are the eriophyid mites (Tetrapodili) (Fig. 205, g). These mites feed by sucking out the contents of individual epidermal Cells, resulting in deformation and discoloration of leaves and buds, as well as The formation of galls of various SHAPES AND SIZES. Eriophyid mites cause particular damage to fruit trees and shrubs. Crop losses in grapes, apples, plums, pears, and citrus fruits can reach 30–70% in certain years.

Spider mites (Tetranychoidea), well-known especially to gardeners, spin fine webs over plant leaves, from which they suck out cellular contents and destroy METABOLISM/14.html">Chloroplasts.

Around 4,000 species of acariform mites (Halacaridae, Hydracarina) (Fig. 205, d) are aquatic, with the majority being freshwater forms inhabiting a wide Temperature range from cold waters to hot springs. They have adapted to life in both standing water bodies and rapid streams, and exhibit tolerance to water pollution. The disappearance of water mites in certain bodies of water is linked to the extinction of various small invertebrates upon which they prey.

The study of mites is a specialized branch of science known as acarology.