Mesostigmata Gamasida

This group of mites is highly diverse; most are free-living but others are ecto- and endoparasites ofreptiles, birds, mammals, and a few insects. They are relatively large, 0.2-3 mm long, and usually heavily sclerotized and brown to reddish brown. Parasitic forms are usually colorless. The principal characteristics of the order relate to the stigmata, which are located near the middle (meso) of the body, next to the coxae of legs 2 and 4, or between legs 3 and 4. The gnathosoma or mouthparts are usually large and distinctly separated from the remainder of the body.

Several mesostigmatid families have free-living species associated with bark beetles, ants, and millipedes. Others are parasites of insects, including the Varroidea mites that infect and injure honey bees. There are species that are ectoparasites of snakes, and several that are internal parasites of domestic animals. The canary lung mite, Sternostoma tracheacolum, invades the lungs of canaries; Pneumonyssoides caninum occurs in the sinuses and nasal passages of dogs. Nymphs and adults of the house fly mite, Macrocheles muscaedomesticae (Fig. i8.2e), prey upon the eggs of Fannia canicularis, Musca domestica and M. vetustissima. The mesostigmatid Fuscouropoda vegetans is also a predator of the house fly and little house fly. The yellowish-brown adult attaches itself to the ventral surface of the base of the house-fly abdomen.

Mesostigmata associated with humans are in three families: Dermanyssidae, Macronyssidae, and Laelapidae. They are blood-feeders (hematophagous) and in natural habitats feed on birds and rodents. However, many are not host-specific, and if their primary host suddenly leaves, they will attack other animals, including humans. Laelaps echidninus and L. nuttalli commonly occur on the house rat, Rattus rattus diardii, in Malaysia.

Predatory mites, Blattisocius dentriticus, b. keegani, B. tarsalis (Fig. 18.3b, c) These predatory mites feed on several species of mites in the family Ascidae, and on eggs of some insects. They are generally found in flour, grain, and grain products, with various seeds, and in medicinal herbs. B. dentriticus females lay about 36 eggs at 70-90% RH. Development from egg to adult takes about 12 days at 20 °C and 70-100% RH. B. keegani occurs in stored food, and in nests of birds and rodents; this mite takes about six prey per day during development in these habitats. Female B. keegani layamaximum offive eggs per dayat 27 °Cand 70-75% RH. Developmentfrom egg to adultis 6 days at 27 °C and 70-75% RH, and 8.7 days at 27 °C and 95-100% RH. Immature stages can live 2-7 days without food. Daily consumption of a single prey egg is sufficient for growth, maturation, and oviposition. Female fecundity is 11-61 eggs during 14 days of life at 27 °C and 70-75% RH. This mite preys on the eggs of the stored-product beetles Cryptolestes, Tribolium, Tro-goderma, and Oryzaephilius; eggs and mobile stages of stored-product mites Glycyphagus and Acarus are attacked. B. tarsalis occurs in animal feeds infested with insectpests. The larvae and nymphs feed on the eggs and larvae of food-infesting pyralid moths. Female mites are carried on the bodies of moths, and they lay eggs on the silk webbing of the caterpillar. Developmentfrom egg to adulttakes aboutra days at27 °C; adults live about i0 days.

Chicken mite, red chicken mite, roost mite, Dermanyssus gallinae (Fig. 18.3d) Adults are 0.7 mm long and gray when unfed, and 1-1.5 mm long and red after a blood meal. The body is striated and the dorsal shield is oval and medially with two rows of setae. Eggs are deposited in cracks and in debris in poultry houses, and in crevices adjacent to bird nests in attics. Development from egg to adult can be completed in 7 days. Adults live for 4 months without feeding. Adults and nymphs remain in harborages during the day, and at night move to attack roosting birds. Infestations in buildings usually originate from active or recently abandoned bird nests in attics and under eaves. This species is cosmopolitan and it attacks domestic chickens and turkeys, pigeons, and wild birds such as sparrows, barn swallows, and starlings. When the normal hosts are not available, the mites will attack mammals, including humans. A related species, D. hirundinis, is also associated with poultry houses.

House mouse mite, Liponyssoides sanguineus (= Alloder-manyssus) (Fig. 18.3e) Adults are 0.6-0.7 mm long when unfed; engorged females are about 1 mm long. The body is reddish black, and the idiosoma is unstriated and setose; the legs are slender and relatively long. The dorsal shield is divided: the anterior portion is slender and elongate, while the posterior portion is small and rounded. The chelicerae are long and whiplike. The house mouse (Mus musculus) is the preferred host, but the mite will feed on rats and other rodents, and will attack humans. Females feed several times, and each feeding is followed by oviposition. Developmentfrom egg to adult can be completed in 17-23 days. Unfed females can live 51 days. Engorged nymphs and adults are found indoors near rodent nests and runways. This mite is a vector ofRickettsia akari,which causes rickettsial pox in humans. It is distributed in the USA, Europe, Ukraine, South Africa, and South Korea.

Tropical rat mite, Ornithonyssus bacoti (Fig. 18.3f) Females are about 1.1 mm long when unfed, and 1.4 mm long when fed. The body is gray to yellowish gray, and it changes to red or reddish black when engorged with blood. They have long setae on their narrow dorsal shield. Females lay eggs in several batches, and hatching occurs in about 36 h; fecundity is about 100 eggs. Developmentfrom egg to adulttakes 7-16 days at 21 °C. Adult females live about 62 days, while unfed nymphs can survive about 43 days. Unfertilized females reproduce parthenogen-etically. Nymphs and adults do not remain on the host, but feed and drop off after every meal. The nymphs and adults are very active and within about 10 days will leave an empty nest or harborage of the host rodent. They can move to attack people in restaurants, warehouses, offices, and dwellings where there is an infestation of rodents, or that have been recently infested. Bites usually occur on the arms and ankles of people near the mites. The bite is painful as the mouthparts of the mite are inserted in the skin; the response is irritation, itching, and dermatitis. This species occurs in tropical and temperate regions in all continents and feeds on the blood of mice and rats. It readily bites humans in rat-infested buildings.

Tropical foul mite, ornithonyssus bursa Adults are about i mm long and adult females have a broadly oval dorsal shield with two longitudinal rows of setae. The sternal plate has two pairs of setae. This species occurs in tropical and subtropical areas on all continents. It is a widespread parasite of domestic fowl and the English sparrow (Passer domesticus); other bird species serve as a host for this mite. Adults can live about 10 days away from an avian host, and mites move from infested nests on the outside (vents and exhaust ducts) or inside to bite humans nearby.

Northern foul mite, ornithonyssus silvarium Adults are about i mm long and adult females have an oval dorsal shield with few and scattered setae. The sternal plate has three pairs of setae. Development from egg to adult can be completed in 7 days, and all stages remain on the host. Heavily infested birds appear gray; such birds lose weight and eventually die from loss of blood. Mites will move from dead birds and attack rodents and humans indoors. This species is a pest ofpoultry and wild birds in north temperate regions of Europe, North America, southern Australia, and South Africa.

Prostigmata (= Trombidiformes, Actinedida) The feeding habits of these mites are variable and range from phytophagous and fungivorous to saprophagous; some are parasitic on vertebrates and invertebrates. Body length ranges from o.i to io mm, and the body surface may be striated. The integument ranges from colorless to bright red in the family Trombidiidae. Stigmata i or 2 are usually in the region of the mouthparts, usually near the chelicerae. Modifications of the legs resultin one or morepairs missing, especially in the vertebrate parasites. Sexual dimorphism may be pronounced, and in some groups females give birth to adults.

Cheyletus eruditus (Fig. 18.4a) Adults are about 0.3 mm long. Chelicerae are large and leg-like, and distinctly chelate. It is a predator of mites and is commonly found in grain storage facilities, stored foods, and in house dust. Females lay 5-i3 eggs per day: most eggs are laid during the first 4 weeks of life in batches and attended by the female; fecundity is about 7i eggs. Development from egg to adult takes 84 days at 9.4 °C and 85% RH, and io days at 3i.5 °C and 85% RH. Adults live i—2 months. Growth and development occur between 8 and 3i °C and at least 52% RH; optimal conditions are about 20 °C and 80% RH. At 20.2 °C and 70% RH mortality is 42%, while at 3i.5 °C mortality is i00%. This might explain why winter survival is low. All stages die at —2 °C and 40 °C. This mite prefers feeding on living stored-food mites, but will attack early-instar insect larvae. Females consume i-3 adult acarid mites each day, or about 2i in a lifetime. Nymphs live 3 months without food. It also occurs in bird and mammal nests.

Clover mite, goosberry mite, Bryobia praetiosa (Fig. 18.4e)

Females are 0.7- 0.8 mm long; this species is one of the largest plant-feeding mites. Body color varies from reddish brown to dark green, and dark red; immature stages may be red. Front legs are longer than the body and about twice the length of the other legs. Females lay about 70 eggs, which are bright red. Development from egg to adult takes about 30 days; optimum development is at2i °C. Above 24 °C and below 4 °C the eggs become dormant or inactive; eggs laid in late fall hatch the following spring. Adults become dormant or inactive from May until September. In eastern USA this mite occurs indoors from October until May. Females are parthenogenetic; males are unknown in the USA and are rarely seen in other parts of the world. It is cosmopolitan and infests and feeds on about 200 species of plant, including grasses, shrubs, flowers, and agricultural crops.

Clover mites occur in large numbers on trees and shrubs, and turfgrass in the urban environment. When large populations develop, mites climb on the outside ofbuildings and enter through windows and doors. If crushed, they will leave a reddish stain. There are several species of phytophagous mites, including other Bryobia, that occur in peridomestic habitats, and invasions of mites in the spring or fall may be by one or more of these species. The brown wheat mite or obscure mite Petrobia latens and winter grain mite Penthaleus major invade houses in large numbers. B. praetiosa often occurs in recently established turfgrass, perhaps before populations of natural predators provide suppression.

Cheyletus Eruditus EggEutrombicula
Figure 18.4 Arthropoda: Acari. (a) Cheyletus eruditus; (b) Pyemotes tritici male; (c) P. tritici female; (d) P. tritici, enlarged female; (e) Bryobia praetiosa female; (f) Eutrombicula alfreddugesi.

Chigger, redbug, Eutrombicula alfreddugesi (= Trombicula) (Fig. 18.4f) Adults are 0.9-1.1 mm long; the cuticle is covered with densely pilose setae, giving the body a velvety appearance. The body is constricted behind the second pair of legs, giving the nymph and adulta figure of-eight shape; body color is often bright red. The larva is oval, without a dense covering of setae. Eggs are laid singly in soil; females lay about 7 eggs per day. Hatching occurs in 4-6 days; fecundity is about 200 eggs. The first stage is inactive and remains within the egg fragments; the six-legged larva emerges in about 7 days and crawls about rapidly in search of a host. Larvae live for about 14 days without feeding. The larva of E. alfreddugesi feeds for 1-3 days (sometimes up to 30 days) and takes only one meal. It then drops to the ground and burrows into the upper layers ofthe soil; after about 1 week, the eight-legged nymph emerges. It feeds for about 7 days on insect eggs and the early stages of insects and other arthropods in the soil. After about 7 days in an inactive stage the adult emerges. Development from egg to adult takes about 55 days. Adults are active, and females become inseminated when they walk over stalked spermatophores that males have deposited on the substrate. There are one or two generations per year; overwintering is in the adult stage in a small cell 2-3 cm deep in the soil. In the tropics the life cycle is short and there are two or three generations per year. This mite is parasitic in the larval stage (chigger) on a wide range ofhosts, including mammals, birds, amphibians, and reptiles. Nymph and adult stages are red (redbug) and they are free-living. This species is distributed from Canada to South America and the West Indies.

Microclimate and vegetation can influence population size and activity patterns of adults and larvae. Larval populations along forest-edge habitats are greatest in areas of high RH, moderate temperature, and low-incident sunlight. The short-to tall-grass transition zone in a forest-edge habitat supports larger populations than a tree-canopy zone. Movement activity of larvae is late afternoon to early evening, and remains at low levels until sunrise.

Chigger dermatitis affects people in many parts of the world, particularly during the summer months in temperate climates. It results from the feeding of chigger larvae on exposed skin. Persons walking among tall grass, brambles, and low vegetation may be attacked and suffer intense itching 3-6 h after exposure. Severe dermatitis, consisting of pustules and wheals, develops on the ankles, knees, and waist. Larvae do not burrow into the skin (contrary to popular belief), but attach to the base of a hair or to the smooth surface of the skin. The chigger does not suck blood. When firmly attached, it injects a digestive fluid that causes disintegration of cells, and this cellular material is utilized as food by the chigger. The skin of the host becomes hardened and a tube is formed into the skin. The chigger lies in this tube and continues to feed, and when engorged it retreats and drops off. The action of the chigger digestive fluid probably causes the irritation and itching within a few hours.

Harvest mite, Neotrombicula autumnalis The larval stage is about 0.22 mm long, but when engorged it is about 0.6 mm long. Body color varies from yellowish white to reddish brown to orange. Eggs are laid in soil and larvae move upwards on the blades of grass and the leaves of low-growing shrubs. Larvae are parasitic; the normal hosts for this mite are small mammals and birds, but humans are bitten when walking or working in infested fields or the edges of woods. The larva feeds on fluids at a wound site on the skin, but does not penetrate below the skin surface; itcompletes feeding in 2-3 days. The eight-legged nymph stage and adult live on the soil surface and are primarily scavengers. This is the harvest mite of Europe.

OtherEutrombicula Several other species are known to attack humans, including E. splendens in eastern USA; E. batatas in Central and South America; E. hirsti and E. wichmanni in Asia, Australia, and the Pacific Islands; E. lahillei in Argentina; E. samboni and E. sarcina in Australia; and E. akamushi in Japan, China, and Indonesia.

Straw itch mite, Pyemotes tritici (= P. ventricosus) (Fig. 18.4b-d) Females are about 0.2 mm long and about 2 mm when gravid; the male is about 0.16 mm long. The body of the female is white to yellowish white; gravid females are distended behind the fourth pair oflegs. Eggs are retained inside the female; they hatch internally and the young develop within the body of the female. Adult mites are extruded at the rate of about 50 per day; fecundity is 150-284 eggs. Males emerge first, and they usually remain on the distended abdomen of the female, clustered around the genital opening. Males mate with female mites when they emerge. Mated females immediately search for a host, while newly born males search for a female. Males remain on the female's abdomen and feed on her. Unmated females produce only male offspring. Broods are produced about every 14 days. Adults are active during warm months. Straw itch mite dermatitis often occurs when there are large populations of the mite's hosts present, such as grain moths, bean andpeaweevil,andwood-infesting beetles. Infestations of the furniture beetle, Anobiumpunctatum,in floor joists of a house may result in mites moving from the beetle larvae in search of a host. This mite is a parasite of numerous species of insects, and some of these host insects infest straw, wheat, stored-food products, and wood. Humans can be attacked, resulting in dermatitis and itching.

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