Astigmata Sarcoptiformes

The feeding habits of these mites is variable and ranges from feeding (filter-feeding) on microorganisms to the maceration and ingestion of solid food material. The important species are associated with grain, flour, dried meat and dried fruit, and the skin of vertebrates. They are small, 0.2-1.2 mm long, without a sclerotized dorsal shield, and yellowish white. Palps are two-segmented and the chelicerae are shaped like pincers. Stigmata and trachea are absent, and respiration is primarily through the thin cuticle. Sexual dimorphism is distinctand the males frequently have copulatory suckers on the tarsi or anal region.

This order includes species in about 10 families thatare associated with humans, including stored products, and the household environment. One group is generally referred to as cheese mites; and another major group is parasitic and called itch mites. Metamorphosis in Astigmata includes the motile hypo-pus stage (deutonymph). Hypopi briefly attach themselves to flies and other insects for dissemination. These individuals lack chelicerae and a mouth, and attach only for the opportunity to disperse. Species in Acaridae and Glycyphagidae infest various stored foods, and handling these products can cause a contact dermatitis called grocer's itch. The Sarcoptidae are itch mites or scabies mites; they burrow into the skin of mammals and cause intense itching. The distinct forms of Sarcoptes are regarded as varieties of S. scabiei. They differ slightly from each other, and exchange hosts. S. scabiei var. suis is parasitic on swine and may attack humans, while S. scabiei var. equi temporarily moves from horse to human.

Dust fragments and dust-associated fungi are eaten by a number ofmite species in the genera Dematophagoides, Europly-phus, and Glycyphagus; these mites are preyed upon by various species of Cheyletus. Other species of mites commonly found indoors associated with house dust include Gymnoglyphus longior, Haplochthonius simplex, Hirstia domicola, H. passericola, and Cosmochthonius reticulatus.

Mites commonly occur in animal feed mills and oilseed stores, and they generally infest cereal storage facilities. In the UK, the three most common species found at these sites were: Acarus siro, Lepidoglyphus destructor, Tyrophagus longior, T. palmarum, and T. putrescentiae.

Carpoglyphus Lactis
Figure 18.1 Arthropoda: Acari. (a) Acarus siro; (b) A. farris; (c) Calo-glyphus berlesei; (d) Carpoglyphus lactis; (e) Dermatophagoides farinae; (f) Euroglyphus maynei.

Grain mite, cheese mite, Acarus siro (Fig. 18.1a) Adults are about 0.4 mm long and opaque white. Infested materials include cereals, processed cereal products, cheese, medicinal herbs, and litter in poultry houses. This mite can infesta variety of food materials, and often lives on fungi. It occurs in house dust and is strongly allergenic to humans. Eggs are laid singly and females produce 1-24 eggs per day; fecundity is about 230 eggs, but is 670 with powdered milk or wheat germ as food, at 20 °C and 80% RH. Development from egg to adult is 78 days at 4 °C, and 9.2 days at 28 °C and 80% RH. Females reared on wheat germ live 42-51 days; males live a few days less. Grain moisture of at least 13.4% is required for survival; feeding and other activity stops at 0 °C. Optimal conditions are 20-25 °Cand 75-80% RH. It is a cosmopolitan species, but is more abundant in temperate regions. Closely related species,

A. farris (Fig. 18.1b) and A. immobilis, infest farm-stored grains and cheese.

This mite feeds on fungi associated with stored foods, including Penicilliumcamemberti,Alternaria spp., Aspergillusfavus, A. candidus, A. repens, A. ruber, A. amstelodami, Trichoderma ligno-rum, and Fusarium moniliforme. It is sensitive to antibiotics and antimicrobial agents, and small amounts of the preservative potassium sorbate, methyl paraben, and calcium propionate inhibit their development; high doses cause mortality. A. siro is killed by a 3-day exposure to 100% carbon dioxide.

Caloglyphus berlesei (Fig. 18.1c) Infested food material includes damp and moldy commodities: wheat, copra, flaxseed, and peanuts. This mite also invades and damages insect, bacterial, and fungal cultures. It is a pest of stored food in Japan. Females lay about 27 eggs per day; fecundity is 588 eggs with a range of 60-1174. Oviposition period varies from 3-26 days. Development from egg to adult is 8 days at 27 °C and 80% RH. Optimal development is at 22-30 °C;

minimum is 16.5 °C. Fungi that support development of this mite include Neospora crassa, Scopulariopsis brevicaulis, Aspergillus wentii,and Penicillium viridicatum.Aclosely related mite species, Caloglyphus anomalus, occurs on decaying onions, fruits, and vegetables. It feeds on the semifluid materials associated with decay.

Dried-fruit mite, Carpoglyphus lactis (Fig. 18.1d) Adults are 0.4-0.5 mm long and pale white. Food infested includes milk products, dried fruits, honey, beer, wine, animal feeds, medicinal herbs, and beehives. It is apestofmiso in Japan. Hypopi have been found in the nests of birds, rodents, and ants. Females lay 20-56 eggs per day for about 14 days, and fecundity is about 278 eggs; hatching occurs in 2-4 days. Development from egg to adult is 9-11 days; thresholds for development are 3 °C and 35 °C and 60% RH. Adults live at 25 °C for

15 days at 60% RH and 29 days at 95% RH. Females live longer than males. Without food, adults can live 97-350 days at 0 °C and 85% RH, 10-57 days at 20 °C, and 3-7 days at 35 °C. The immature stages are less tolerantofstarvation than adults. This species is cosmopolitan.

American house dust mite, and European house dust mites, Dermatophagoides farinae (Fig. 18.1e) and D. pteronyssinus

Adult females are about 0.5 mm long and males are about 0.4 mm long. The body is striated and yellowish white, except for areas of sclerotized integument that are light brown. Setae on the ventroposterior margin are short in D. farinae and long in D. pteronyssinus. Infested materials and food include animal feeds, flour, and human skin scales.

D. farinae Females lay 0-5 eggs per day for at least 31 days. Hatching occurs in about 38 days at 16 °C and 75% RH, 10 days at 23 °C, and 5 days at 30 °C and 35 °C. Fecundity is 31-100 eggs at 23 °C and 75% RH. Development time for males and females at 16 °C and 75% RH is about 140 days; at 23 °C it is about 36 days; and at 30 °C it is about 17 days. Most D. farinae do not develop to adult stage at 16 °C and 35 °C.

D. pteronyssinus Females lay about 2.5 eggs per day at 23 °C, and 3.3 eggs per day at 35 °C. Hatching occurs in 26 days at

16 °C and 75% RH, 8 days at 23 °C, 5 days at 30 °C, and 4 days at 35 °C. Fecundity is about 65 eggs at 23 °C, and about 50 eggs at 35 °C. The percentage of eggs that successfully develop is 59% at 16 °C, 86% at 23 °C, 81% at 30 °C, and 87% at 35 °C. Development time for males and females at 16 °C and 75% RH

is about 123 days, 34 days at 23 °C, 19 days at 30 °C, and about 15 days at 35 °C.

Development for D. pteronyssinus is optimal at 25 °C and 70-80% RH; populations do not grow well at humidities less than 60%. Optimal development for D. farinae is at 25-30 °C and 50-80% RH; critical RH for the female is 55-73%. Dust mites survive for long periods in buildings with humidities less than 50%. For these animals, the rate of water uptake exceeds the rate ofwater loss, and periods when the RH is high supplies mites with sufficient water to compensate for low RH levels. These two dust mite species are cosmopolitan. Their separation in geographic occurrence is correlated with their humidity requirements for survival. D. farinae occurs more often in dry inland sites, and D. pteronyssinus in regions with humid or coastal climates.

Natural habitats for these two Dermatophagoides include bird nests, on birds, and inmammal nests and burrows. In the urban environment these species occur predominantly indoors, in some stored food, on the floor in house dust, on clothing and upholstered furniture in commercial (including schools, hospitals, hotels) and residential settings, in automobiles, and other types of transportation. House dust is composed primarily of particles that are 0.01-1 mm in diameter, including human skin scales or flakes, cotton fibers, paper fibers, wool, synthetic fibers, mite feces, and mite exuviae. House dust samples range from 32 to 100% positive for species of Dermatophagoides, and they constitute 43-100% of the mite fauna indoors. The number of these mites in a 5-g dust sample may reach 4390. Distribution of mites indoors is centered in areas ofhuman activity, and determining the number ofmites per square meter is an accurate method ofexpressing the level of infestation. Populations fluctuate, and are usually higher in summer than in winter. These mites feed on cast skin flakes (from humans and indoor dog and cat pets), hair, and other detritus, along with the fungi that grow on skin flakes. Humans shed 0.5-1 g of skin scales per day. The fungus Aspergillus repens, which is carried on the body of dust mites, renders the skin flakes into a form that the mites can utilize as food. Allergens produced cause rhinitis, eczema, andasthma, affecting 50-100 million people worldwide. These allergens are contained primarily in dry mite feces, which are pellets 20-50 ^mindiameter and covered with a peritrophic membrane (produced in the gut ofthe mite). Mites produce about 20 fecal pellets a day, which readily become airborne. Other allergens are presentin the cast exuviae.

Extracts of Dermatophagoides mite bodies contain about 30 different protein molecules called allergens. The important allergens are called Derp I, Derp II, Derp III, Derp IV, and Derfl. The Derp and Derfare abbreviations of the scientific name of the mites (D. pteronyssinus, D. farinae). People allergic to house dust mites react to two or more of these proteins, and most people have a different combination of reactiveness. The ability of an allergen to sensitize an individual is related to its immunogenic properties, the susceptibility of the individual, and the degree of exposure. The proportion ofindividuals in an exposed population who become sensitized is probably under some genetic influence. While genetic influences and factors such as tobacco smoke and other pollutants are important, the level of the allergen in the environment plays the primary role. For the allergen Der p I, levels of 2 ^g/g of dust may be the threshold for sensitization. The response occurs for the first time at any age, and infants are particularly susceptible. Seasonal changes and cultural habits, such as routine cleaning, cause fluctuations in mite populations, and these are accompanied by increasing or decreasing levels of mite allergens in house dust. Physiological actions such as enzymatic degradation of skin scales, and house dust-inhabiting fungi and bacteria also contribute to the decay of allergens, and influence allergen levels.

Other Dermatophagoides Other species in the genus have been isolated from natural habitats, such as bird nests, and from indoor habitats, such as house dust and stored food. These include D. evansi, D. chelidonis, D. bakeri, and D. scheremetewski.

Euroglyphus maynei (Fig. 18.1f) Adults are about 0.4 mm long. The body is distinctly pointed anteriorly; the cuticle is sclerotized and it has striations dorsally and ventrally. Legs are cylindrical; the epistome terminates with two points. Male legs are of equal length, while female legs 3 are shorter than legs 4. Females lay 1.3 eggs per day over 25 days at25 °C and 75% RH. Female nymphs emit a pheromone that induces male guarding behavior. This species is a common inhabitant ofhouse dust, especially in temperate latitudes, and it has been shown to be highly allergenic. In dwellings where this species is present in large numbers, it may make a considerable contribution to the allergen pool. It occurs primarily in humid habitats, and is common in mattresses, which retain moisture for long periods. This species is distributed around the world.

House mite, Glycyphagus domesticus (Fig. 18.2a) Adults are 0.3-0.7 mm long; females are larger than males. The body has long and feathered setae posteriorly, while the legs have long setae. Food infested includes a variety of plant and animal materials, including flour, wheat, cheese, ham, and fish. It occurs in medicinal herbs and animal nests, such as the European house sparrow (Hirundo rusticus). It occurs in house dust and is strongly allergenic. Females lay 91.5 eggs per day at 15.6 °C and 98% RH, and 135.4 eggs at 20.6 °C; oviposition lasts 20-29 days. Development from egg to adult is 56.5 days at 11.7 °C and 95-100% RH, and 22.5 days at 23.3 °C and 98% RH. Fungi that support development of this mite are Nigrospora sphaerica, Hormodendrum cladosporioides, and Scopulariopsis brevicaulis.

Inert hypopi enclosed in the protonymphal cuticle often occur in house mite populations; 50% of the protonymphs develop through this stage. It is resistant to dry conditions and remains viable for several years. Hypopi occur at 25-30 °C and 75-95% RH. Development from hypopus to adult takes 4-5 weeks. A closely related species, Glycyphagus cadaverum (= G. spinipes), occurs in dry animal and plant material outdoors and indoors.

Aquarium mites, Histiostoma anguillarum, H. cyrtandrae, H. nigrelli, H. piscium Although there are many aquatic mites in natural habitats, only a few species are known from artificial aquatic habitats, such as swimming pools and aquaria. These Histiostoma have been reported from large aquaria in the USA (aquaria of New York Zoological Society) and Europe (aquaria in Antwerp).

Histiostoma ocellatum Adults are distinguished by the copu-latory orifice that leads to a bursa surrounded by a sclerotized structure. The propodonotal shield bears a faint pattern of lines, which become inconspicuous in the posterior half. This mite occurs in indoor swimming pools in Japan, and in some locations it is the dominant mite species. Adults and nymphs are found, indicating a successful population.

Lardoglyphus konoi Infested foods include dried and salted fish in India, Japan, and European countries. Optimal conditions are 30 °C and 83% RH in fishmeal. Development from egg to adulttakes 8.5 days at35 °C, and 9-11 days at23 °C and 87% RH. Motile hypopi appear at 20-30 °C and 76-94% RH. The hypopi are typically carried by insects, especially Dermestes and Necrobia beetles.

Ear mite, Otodectes cynotis Adults have long setae on legs 3 and 4; legs 1 and 2 have elongate claws. Leg 4 is the smallestin both sexes. This auricular mite lives in the ears ofdogs, cats, ferrets, and foxes. Adultand immature stages feed on dead skin

Thyreophagus Entomophagus
Figure 18.2 Arthropoda: Acari. (a) Glycyphagus domesticus; (b) Rhizoglyphus robini; (c) Thyreophagus entomophagus; (d) Sarcoptes scabiei; (e) Macrocheles muscaedomesticae; (f) Tyrophagus putrescentiae.

tissue and complete their life cycle within the inner cavities of the ear. An infestation of these mites, otacariasis, causes irritation, liquid discharge from the ears, and rubbing, scratching, and head-shaking by the animal. Severe infestations can result in damage to the inner ear and loss of balance. This mite is common in domestic house pets around the world. It does not infect humans.

Bulb mite, Rhizoglyphus echinopus Adults are 0.5-0.7 mm long. The body is oval, usually with two brown spots laterally; the chelicerae and legs are brown. Immature stages have brown spots and brown legs. Females lay 2-26 eggs per day; fecundity is about 100 eggs when reared on onions and flower bulbs. Development from egg to adult (excluding the hypopal stage) is 8-14 days at30 °C, 38-50 days at 10 °C, and 123 days at 5 °C. Optimal development is between 20 and 30 °C and 85% RH. Fungi that support development of R. echinopus include

Aspergillus repens, Botrytis cinera, and Trichothecium roseum. These mites are usually found in large numbers, and because of their oval shape and slow movements they are often mistaken for insect eggs. Flower bulbs, primarily gladiolus, hyacinth, and onions, are attacked in the field and in storage. They cause irritation from contact with excretions as the mite walks on the skin. Other Rhizoglyphus associated with bulbs include R. robini (Fig. 18.2b).

Scabies, itch mite, sarcoptes scabiei (Fig. 18.2d) Adult females are 0.3-0.4 mm long and 0.2-0.3 mm wide; males are about half as large. The body is rounded and the cuticle is striated, with specialized dorsal scales and setae. Legs are arranged in two groups: the anterior pair in both sexes end in stalked pulvilli, which assist in gripping the host; the posterior pair end in long setae, but in the male only the third pair ends in setae. Females move about 2.5 cm/min over the skin surface and select a site for making a burrow and oviposition. Preferred sites include between the fingers, at the bend ofelbow and knee, and at other sites of soft skin. Eggs are deposited at 2-3-day intervals for about 2 months, and the tunnels in the skin may extend 3 cm. Hatching occurs in about 5 days, and newly hatched larvae move to the surface of the skin. Nymph development into adults takes 4-6 days. Females make a temporary burrow in the skin before mating. Males also burrow, but their burrows are no more than 1 mm long. Development from egg to adult requires 10-14 days. Peaks in the incidence of human scabies occur in 15-20 cycles, and this might be due to fluctuating levels of immunity in the human population. This species is widespread in the tropics and in temperate regions.

Scabies mites are usually transmitted from person to person, and infestations are common in dormitories, health- and mental-care facilities. These mites have acute sensory abilities and well-developed host-seeking behavior. They perceive specific host stimuli and will actively move from host to host. They respond independently to both thermal stimuli and host odor. In close proximity, both of these stimuli are effective; at a greater distance host odor is more effective. These mites die quickly away from the human body. S. equi is associated with horses and mules and may transfer to humans and cause a temporary skin irritation.

Thyreophagus entomophagus (Fig. 18.2c) Adults are 0.30.6 mm long. The body is shiny white, and the mouthparts and legs are yellowish white to light brown. The dorsal suture is distinct; there are long setae on the legs and body. Materials commonly infested include flour, cereal products, animal feeds, spices, medicinal herbs, and insect collections. Female fecundity is about 76 eggs, and the maximum is about 170; the oviposition period lasts about32 days. Development from egg to adulttakes abouti5.5 days. Growth and development occur between 3 and 32 °C and 75-100% RH. Optimum conditions are 15-25 °C and 85% RH. Adult females live about 46 days and males about 41 days; they can live 2 years at 3-5 °C, and 9 months at 6-10 °C. A closely related species, T. carpio, is associated with decaying hardwoods.

Mold mite, Tyrophagus putrescentiae (Fig. 18.2f) Adults are about 0.5 mm long. Chelicerae are enlarged; dorsally there are four long setae anteriorly and numerous long setae on the dorsoposterior margin, and four long setae on the ventro-posterior margin. Food infested includes grain, wheat, flour, peanuts, cottonseed, rapeseed, sunflower seed, tobacco, dried fruits, dried eggs, cheese, and medicinal herbs. It occurs in commercial mushroom houses, and it often infests laboratory cultures ofinsects and microorganisms. These mites occur in large numbers in rice-straw mats (tatami) in houses, and they are a common allergen in house dust. Females lay about four eggs per day, but can deposit a maximum of 60 per day; fecundity is about 500 eggs for females that mate twice a month, depending on the food source. Females reared on wheat germ or yeast produce about 500 eggs, while those reared on rolled oats produce about 8. About 70% of the eggs are produced during the first 3 weeks of the female's life. Development from egg to adult takes 9.5 days at 25 °C and 85% RH, and 130 days at 8.5 °C and 85% RH. At 25 °C and 85% RH females reared on wheat germ live about 66 days, males about 59 days.

Medicinal herbs are often infested by T. putrescentiae. This mite responds favorably to many volatile oils and alkaloids, and to robinin and rutin in their food. It is generally unaffected by antibiotics and antioxidants added to food it infests. It can feed on insect eggs, butitis essentially a fungivore. Numerous fungi can support normal growth and development: Polyporus spp., Poria spp., Stereum spp., Flammula spp., Alternaria tenuis, Aspergillus versicolor, A. candidus, A. amstelodami, Fusarium monil-iforme, Helminthosporium sativum, Mucor racemosus sphaerosporus, Nigrospora sphaerica, Stemphyliumbotryosum, Trichotheciumroseum, Botrytis cinerea, Penicillium purpureum, and P. chrysogenum.

Tyrophagus longior (Fig. 18.3a) Adults are about 0.5 mm long. The anterodorsal sclerotized plate has four plumose setae on the anterior margin, four short, plumose setae medially, and four long, plumose setae posteriorly. Materials infested include grains, cereal products, drugs, seeds, cheese, dried fruits, and prepared foods of animal and vegetable origin. It generally prefers substrates with a high moisture content, but not actually moldy or decomposing. Development from egg to adult takes 2-3 weeks at 23 °C and 87% RH. This species is probably native to Europe, but the current distribution is nearly worldwide.

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