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  Biology of Major Economically Important Mites, Biology tutorial

Introduction:

Mites are a much significant and highly specialized group of the Arachnids. They are more abundant than ticks. Mites frequently take place in fantastic numbers, particularly in soil and litter where they are significant in litter decomposition particularly in dry regions.

However mites are not insects, entomologists are frequently termed as on to deal with them due to their agricultural significance. Mites are economically significant in that a few species attack food, example: flour mite and cheese mite. A few attack on the living plants. Other attack man, example: scabies is mainly caused due to the hair follicle mite, Sarcoptes scabei. 

Most of the free living mites are predaceous carnivores whereas others are omnivorous scavengers. The great variety of feeding habits among mites is associated to the miniaturization which characterizes the group.

Body Structure of Mites:

Dissimilar to insects, having bodies categorized into head, thorax and abdomen, the arachnid body is ancestrally splitted into two functional units, the prosoma (that is, the first six body segments) and the opisthosoma (that is, the remaining segments). The body of a mite is additionally transformed in that such original units are fused. A secondary subdivision separates the first two body segments into a structure known as the gnathosoma, specialized for feeding, and the remainder of the body, known as the idiosoma, having organs of digestion, locomotion and reproduction.

Most of the mites exhibit no proof of external body segmentation, other than the serial appendages. The gnathosoma bears the primary two pairs of appendages, the chelicerae that might retain the ancestral chelate or pincer-like form, or might be highly transformed as stylets for piercing and sucking; the pedipalps, which might be nearly leg like, are strongly transformed for grasping prey or joining to a host or highly reduced. The anterior idiosoma in general bears four pairs of walking legs, the primary pair of which might be transformed as antenna-like, sensory structures. Legs might as well be modified for joining to a host. Occasionally legs of males are transformed for grasping a female throughout mating or for Intraspecific combat. The mite's body cuticle might be completely soft, categorized into a number of hard, sclerotized plates or almost wholly sclerotized. In some mites, crystalline, mineral salts as well strengthen the cuticle. These modifications balance the requirements for flexibility in the movement and protection from predators.

The body surface bears setae, usually hair-like sensory organs, arranged in the characteristic patterns in various subgroups of mites. Setae are mainly hair-like, however might take on an incredible diversity of shapes, from thick spines, to flat plates, to highly branched, feather-like forms. The pedipalps and legs as well bear tactile setae and also chemosensory structures named solenidia that are organs of taste and smell, and other specialized sensilla which are sensitive to infrared radiation. Simple eyes or ocelli might be present on the anterior idiosoma and specialized sensory organs, the trichobothria, on the anterior idiosoma or legs might notice vibrations or electric fields. Similar to other arthropods, the internal of a mite's body is a hollow cavity, the hemocoel, in which the internal organs are surrounded through fluid, the hemolymph. Hemolymph shares food materials and waste products and consists of hemocytes that are the cells which serve as the immune system of mite; however it doesn't have oxygen-binding proteins as are found in the blood of vertebrates and a few other arthropods.

The digestive system of mite is categorized into three portions typical of arthropods: foregut, midgut and hindgut. The midgut might be categorized into diverticulae for food storage, specifically in parasitic mites. A few mites lack a relationship between the midgut and the hindgut; such mites feed just on fluids and don't defecate. The hindgut in such mites is modified into an excretory organ for the removal of nitrogenous wastes. Other mites, having entire guts, might encompass Malpighian tubules, such as insects, extending from the junction of the midgut and hindgut as the excretory organs. The internal reproductive system usually comprises of a single ovary (that is, paired in the Astigmata) in the female and paired testes in the male.

Females usually have a spermatheca for sperm storage subsequent to insemination and both sexes encompass a variety of accessory glands and ducts to the exterior as part of the system. Tracheal systems for respiration have evolved separately a number of times in the Acari. Such open at spiracles, or stigmata, on different portions of the body in various groups. Other mites are deficient in any respiratory system, and gas exchange takes place via the cuticle in such groups.

Biology of the Itch Mite (Sarcoptes scabiei):

Sarcoptes scabiei or the itch mite is a parasitic arthropod which burrows into skin and causes the scabies. Animals influenced comprise not just human however as well wild and domesticated cats and dogs in which it is one cause of mange. As well influenced in the wild are ungulates, boars, wombats, bovids, koalas and great apes. 

1) Morphology:

The adult scabies mites are spherical, eyeless mites having four pairs of legs. They are familiar by their oval, ventrally flattened and dorsally convex tortoise-like body and multiple cuticular spines. Females are around 0.3 to 0.45 millimeter long and 0.25 to 0.35 millimeter wide and males are just over half that size.

2) Lifecycle:

The scabies mite Sarcoptes scabiei var. hominis goes via four phases in its lifecycle: egg, larva, nymph and adult.

On infesting a human host, the adult female burrows into the skin, where she deposits 2 to 3 eggs per day. Such oval eggs are around 0.1 to 0.15 millimeter long and hatch as larvae in 3 to 4 days. On hatching, the 6-legged larvae migrate to the skin surface and then burrow to the molting pouches (that is, these are shorter and smaller than the adult burrows). After 3 to 4 days, the larvae molt, turning into 8-legged nymphs. This makes molts a second time into slightly bigger nymphs, before a final molt into adult mites. Adult mites then mate if the male penetrates the molting pouch of the female. Mating takes place only once, as that one event leaves the female fertile for the rest of her life (1 to 2 months). The impregnated female then leaves the molting pouch in look for an appropriate place for a permanent burrow. Once a site is found, the female makes her characteristic S-shaped burrow, laying eggs in the procedure.

The female will carry on lengthening her burrow and laying eggs for the period of her life.

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