INVERTEBRATE ZOOLOGY - H. I. Shcherbak - 2008

KINGDOM MULTICELLULAR ANIMALS (METAZOA)

SUBKINGDOM TRUE MULTICELLULAR ANIMALS (EUMETAZOA)

SECTION TRIPLOBLASTIC (TRIPLOBLASTICA) OR BILATERAL (BILATERIA) ANIMALS

SUBSECTION MOLTING ANIMALS (ECDYSOZOA)

PHYLUM ARTHROPODS (ARTHROPODA)

SUBPHYLUM CHELICERATES (CHELICERATA)

SUPERCLASS ARACHNIDS (ARACHNIDA)

CLASS MITES AND TICKS (ACARI)

Ticks and mites (Acari) are among the most widespread groups of animals on Earth. They have been found on all continents, including Antarctica. The majority of them are free-living organisms inhabiting soils, leaf litter, and various decaying organic matter, and they can also be found in human dwellings. Some species inhabit freshwaters, as well as seas and oceans. About 50,000 species have been described, which represents only a small fraction of those existing in nature. Approximately 3,000 species have been recorded in Ukraine.

Among free-living mites, There are many predators and saprophages, as well as necrophages and facultative hematophages. The Study of free-living mites is still in its infancy; hematophagous and parasitic species have been investigated in greater detail. These parasites inhabit bird feathers, as well as the integument, respiratory, digestive, and reproductive systems of numerous invertebrates, vertebrates, and humans.

Most mites and ticks are microscopic organisms up to 1 mm in size, much less commonly reaching 2.5–7 mm, and only ixodid ticks can grow up to 25–30 mm after a Blood meal.

Morphology. Mites and ticks are distinctly separated from other arachnids by a combination of the following features: the mouthparts, along with the chelicerae and pedipalps, are demarcated from the body (idiosoma) into a distinct false HEAD known as the gnathosoma; the segmentation of the idiosoma is indistinct or entirely lost (Fig. 292, e). The gnathosoma is typically located anterior to the idiosoma and is connected to it by a mobile, elastic membrane. The shape of the idiosoma can be oval, egg-shaped, and more rarely spherical, pear-shaped, or nearly triangular. In some species, the body is worm-like. The details of the chelicerae and pedipalps vary greatly, and their Structure depends on the lifestyle of the Organism.

In the larval phase, mites and ticks typically have three pairs of legs, while the nymphal and adult stages possess four pairs. The legs function primarily for locomotion, although in certain groups, the first pair of legs loses its locomotor function and acquires a sensory role. In aquatic mites, the legs are adapted for swimming, while in many parasitic groups, numerous specializations develop on the legs for clinging to bird feathers, mammal fur, and the like. Mites and ticks are also frequently brightly colored.

The smallest mites respire through their entire body surface, whereas larger ones possess a tracheal system.

Reproduction. Fertilization is generally spermatophoric, although in some groups the male releases a droplet of seminal fluid that is drawn into the genital cone by the trailing female. In many species of mites, only a single egg develops at a time, and the female produces a small number of eggs over her lifetime.

The life cycle of mites and ticks most prominently features the following phases: egg, larva, nymph, and adult (imago). The nymphal phase may include several stages: proto-, deuto-, and tritonymphs. The larva, as noted above, has three pairs of legs. Quite often, the life cycle is simplified, comprising only one or two nymphal stages.

Parthenogenesis is quite common among mites and ticks, notably arrhenotokous parthenogenesis (arrhenotoky), where unfertilized eggs develop exclusively into males, and thelytokous parthenogenesis (thelytoky), where they develop solely into females.

All mites and ticks are divided into three major orders.

Order Opilioacarina (harvestman-like mites, Fig. 304) represents a small group comprising 12 known species of free-living nocturnal predators that feed on small soil-dwelling animals, and may also consume plant pollen and fungal spores.

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Fig. 304. The harvestman-like mite Opilioacarus segmentatus

(after Baker and Wharton)

Order Parasitiformes. Among these, the most thoroughly studied are ixodid ticks, which are hematophagous temporary ectoparasites of vertebrates, including humans, and act as specific vectors for numerous viral, rickettsial, and bacterial natural focal diseases. Ixodid ticks are distributed across all continents except Antarctica. Approximately 700 species have been described, including 30 species within the fauna of Ukraine.

The best-known vectors of human tick-borne encephalitis pathogens are the taiga tick (Ixodes persulcatus), found in the forests of the Russian taiga zone (Fig. 305), and the castor bean tick (Ixodes ricinus), an inhabitant of Europe and North Africa (Fig. 292, e). Equally notable vectors include Rhipicephalus sanguineus, which transmits Mediterranean spotted fever, and ticks of the genus Dermacentor, which transmit spotted fever in the Americas. Ixodid ticks are also vectors for pathogens causing severe animal diseases, notably hemosporidioses.

Fig. 305. Parasitiform mites:

a - taiga tick (Ixodes persulcatus) in waiting posture (from Filippova); b - gamasid mite Allodermanyssus sanguineus (from Shcherbak);

c - Varroa destructor (from Akimov et al.)

Parasitiform mites also include a large group known as gamasid mites (Gamasina). About 5,000 species have been described; most of them are free-living predators, but There are also parasitic species, including hematophages. The well-known poultry mite (Dermanyssus gallinae) belongs to this group. Urban residents often encounter them in their homes, where the mites crawl in from pigeon nests, especially after the birds abandon them. Bites from these mites can cause acute dermatitis.

The gamasid mite Varroa destructor (Fig. 305, c) is infamous; in the 1970s, it began to spread rapidly across Ukraine, causing enormous damage to beekeeping. These mites feed on the hemolymph of pupae and adult bees.

A great hazard to humans is posed by the house mouse mite Allodermanyssus sanguineus, a specific vector of rickettsialpox, a disease also found in Ukraine (Fig. 305, b).

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

Order Acariformes (acariform mites). They occur both on land and in marine and freshwater bodies. Among them are free-living forms, including serious pests of stored agricultural products, as well as parasites of plants, animals, and humans. However, there are few vectors of infectious diseases among them, although chigger mites of the family Trombiculidae (Fig. 306, a) transmit the CAUSATIVE AGENT OF Japanese river fever (tsutsugamushi disease) to humans.

Fig. 306. Acariform mites (from Baker and Wharton):

a - chigger Trombidium; b - oribatid mite Galumna; c - itch mite Sarcoptes scabiei; d - eriophyid mite Oxypleurites;

e - Water mite Hydrarachnxa geographica: 1 - gnathosoma; 2 - chelicera; 3 - pedipalp; 4 - idiosoma

Acariform mites include Oribatei (oribatid mites), the largest group among soil and litter mites, which function as saprophages, phytophages, and mycophages (Fig. 306, b). Their population density can exceed 1 million/m². Oribatid mites play an active role in humidification processes and the biogeochemical cycling of elements in agricultural, forest, and other soils.

The group Acaridiae (acaridid mites) has long been known, including grain or flour mites (Acaroidea), which damage grain reserves in elevators and warehouses as well as other food supplies such as dried fruits and hard cheeses, and also proliferate On the surface of wine. Ingestion of these mites with food can lead to acute gastrointestinal disorders. Recently, they have been increasingly recognized as agents of various allergic diseases, primarily atypical forms of Bronchial Asthma.

Among endoparasitic acaridid mites, the human itch mite (Sarcoptes scabiei), which parasitizes within the epidermis (Fig. 306, c), is the primary causative agent of Scabies. Ectoparasitic acaridid mites are represented by highly specialized feather mites of birds and Hair mites of mammals.

Mention should also be made of Demodex folliculorum mites, which parasitize the Sebaceous Glands and hair follicles of the human face and ears. They are often referred to as face mites. It has now been established that they can also inhabit completely healthy Tissues. In The Development of follicular mange, staphylococci are always present alongside the mites and serve as the true causative agents of the disease.

Serious plant pests include minute worm-like eriophyid mites (Tetrapodili, Fig. 306, d) and spider mites (Tetranychoidea).

About 4,000 species of acariform mites (families Halacaridae, Hydracarina) (Fig. 306, e) live in water; the majority are freshwater forms found in waters with a wide Temperature range.