Common Name: House Dust Mite
Scientific Name: Dermatophagoides spp., etc.
Class/Order/Family: Arachnida/Acari/Pyroglyphidae
Metamorphosis: Simple
Introduction
The common name comes from the association of these mites, their skeletal parts, and/or fluids with house dust. Although these mites do not bite, they are estimated to be responsible for the allergic reactions. Although there are several species of house dust mites, this section will be restricted to the 2 most common species found worldwide. These are the American house dust mite, Dermatophagoides pteronyssinus (Trouessart).
Recognition
Adults about 1/64″ (0.33 mm) long. Body oval, soft, somewhat dorsoventrally flattened (top to bottom). Color off-white to cream. Dorsum with fine striae/grooves not interrupted/broken by sharp projections, without punctures/pits; propodosoma (dorsal, front area) not prolonged by a forked or pointed extension; external (towards outside) scapular hair/seta much longer and thicker than internal (to inside) scapular hair/seta (dorsal pair of hairs to either side about midway between midline and lateral margin, approximately in line with 2nd pair of legs); hysterosomal/rear shield absent; male posterior margin bilobed, with 10 hairs/setae; and metapodosomal venter (between 3rd and 4th pair of legs) without ringlike structures.
Mouthparts with chelicerae relatively short, chelate (mandible like); palpus short, simple (unmodified), apical sensillae (thick bristles) short, unmodified. Stigmata (breathing pore opening plate) absent. Legs with 4th pair inserted on posterior/rear portion of idiosoma/body; tarsi stout, usually not more than twice as long as adjacent tibia, tarsi of 3rd pair of legs without spines, tarsal tip bearing a minute claw (empodium) surrounded by large discoid/bell-shaped pulvillus. Genital opening (about between 4th pair of legs) an inverted “U”. Anus (near ventral rear margin along midline) with surrounding sucker plate surrounded by lateral/hardened arcs/ridges. Hypopdial stage (hypopus) absent.
Similar Groups
(1) Dermatophagoides chelidonis males (smaller, darker) with hysterosomal shield (rear end) on venter not reaching coxae of 4th/rear pair of legs, shield as long as wide, and 3rd leg twice as long as 4th leg; females (larger, paler) with pair of long rear dorsal hairs/setae and 2 long rear lateral (one each to outside of dorsal pair) hairs/setae not coming from a shield, and internally with base of seminal receptacle simple, not swollen.
(2) Dermatophagoides evansi males (smaller, darker) with hysterosomal shield on venter reaching coxae of 4th/rear pair of legs and tarsus 1 (1st pair of legs) with 3 terminal spines and tarsus II (2nd pair of legs) with 1 terminal spine; females (larger, paler) with pair of long rear dorsal hairs/setae and 2 long rear lateral hairs/setae arising from a punctuated/pitted shield, and internally with base of seminal receptacle goblet-shaped.
(3) Euroglyphus longior with external and internal scapular hairs/setae (dorsal pair of hairs to either side about midway between midline and lateral margin, approximately in line with 2nd pair of legs) subequal in length; males (smaller, darker) with anal suckers present and thickened arcs/ridges to outside of suckers, and rear body margin with 2 distinct lobes with 3 hairs/setae each; females (larger, paler) with internal base of seminal receptacle simple, not swollen, external genital opening club like and not terminal, and vulva (external genital opening on genital plate) covered with a membrane.
(4) Parasitic mites such as chicken (Dermanyssus gallinae), human itch (Sarcoptes scabiei var. Hominis), northern foul (Ornithonyssus sylviarum), straw itch (Pyemotes tritici), etc. mites usually with distinctive dorsal and/or ventral shields and tarsi with tip not bearing a minute claw (empodium) surrounded by a large discoid/bell-shaped pulvillus.
(5) Chiggers (larval Trombiculidae) with 6 legs and color red to reddish orange.
Representative Species
1. American house dust mite, Dermatophagoides farinae Hughes. Sclerotized process at apex of tarsus I (1st pair of legs) large, spinelike; male (smaller, darker) with 1st/front pair of legs thicker than other legs, giving a somewhat crablike appearance, 3rd leg 1.5 times as long as 4th leg, hysterosomal shield (rear end) on venter not reaching coxae of 4th/rear pair of legs, shield as long as wide; female (larger, lighter in color) with pair of long rear dorsal hairs/setae and 2 long rear lateral (one each to outside of dorsal pair) hairs/setae not coming from a shield, and internally with base of seminal receptacle only slightly swollen not daisy like or goblet-shaped, and distal end (=bursa copulatrix) heavily sclerotized (thickened/hardened); found in England, Japan, Netherlands, Russia, Sierra Leone, and the United States.
2. European house dust mite, Dermatophagoides pteronyssinus (Trouessart). Males (smaller, darker) with 1st pair of legs thin, like rest of legs, tarsus I (1st pair of legs) with 1 terminal spine like process and tarsus II (2nd pair of legs) lacking terminal spine, and hysterosomal shield (rear end) on venter reaching coxae of 4th/rear pair of legs; female (larger, lighter in color) with pair of long rear dorsal hairs/setae and 2 long rear lateral (one each to outside of dorsal pair) hairs/setae not coming from a shield, and internally with base of seminal receptable expanded, daisy like and disal end (=bursa copulatrix) slightly sclerotized/hardened; found essentially worldwide.
Biology
Developmental stages include egg, larva, protonymph, tritonymph, and adult. Larvae have only 3 pairs of legs whereas, nymphs and adults have 4 pairs. The developmental time (egg to adult) for these 2 species can be summarized as the average number of days required for the egg, larvae, protonymph and tritonymph stages respectively at 75% RH, and is as follows:
1. American house dust mite; At 61F/16C, 39,5027, and 24.1, total of 140.1 days. At 75F/23C, 10, 9.2, 8.6, and 7.7, total of 35.6 days. At 86F/30C, 5.1, 4.9, 3.8, and 3.8, total of 17.5 days. At 95F/35C, 5.4, 5.8, 5.6, and 5.4, total of 22.1 days. It should be noted that at 61F/16C, only 15% completed development and at 95F/35C, only 2% completed development.
2. European house dust mite. At 61F/16C, 26.6, 37.4, 28.8, and 30, total of 122.8 days. At 75F/23C, 8.1, 10.4, 6.9, and 8.3, total of 34 days. At 86F/30C, 5.1, 4.9, 3.8, and 3.8, total of 17.5 days. At 95F/35C, 3.9, 4.2, 3.4, and 3.5, total of 15 days. The % which completed development at the 4 temperatures starting with 61F/16C was 59, 86, 81, and 87 respectively. Fecundity (average egg production) and longevity at 75F/23C and 75% RH can be summarized as follows:
1. American house dust mite. Females produced an average of 66 eggs (range 31-100) each. Mated females lived an average of 100.4 days, including an average of 63.3 days after egg laying stopped. 2. European house dust mite. Females produced an average of 68 eggs (range 19-158) each.
Mated females lived an average of 31.2 days, including an average of 1.8 days after egg laying stopped. Under optimal conditions, the protonymph and tritonymph of the European house dust mite can undergo a prolonged quiescent period of several months during which they are highly desiccation-resistant. The American house dust mite protonymph and tritonymph probably do not exhibit the same quiescent behavior under optimal conditions. House dust mites are responsible for the allergic reactions of millions of people and may be a factor in 50-80% of asthmatics. People react to some proteins found in their excrement and exoskeleton fragments.
Habits
House dust mite development, fecundity, and longevity are very dependent on temperature, moisture, and an adequate food supply. Therefore, they select certain microclimates within a structure which provide these needs. These mites feed on sloughed human skin, spilled foodstuffs, fungi, and pollen. The average adult human sheds about 70-140 mg of skin scales each day, and about 180 mg of this material is sufficient to produce and maintain mass cultures of the European house dust mite for several months.
Highest concentrations of sloughed skin scales occur in bedding, mattresses, upholstered furniture, carpets, and in stuffed toys. Humans supply the necessary increase in moisture and temperature over ambient room levels when they frequent these area. Bedding ans stuffed furniture provide the best conditions because humans spend more time there, with carpeting being the least favorable because of lower moisture. A gram of dust vacuumed form carpeting may contain 100-400 mites whereas, a gram of dust from stuffed furniture may contain 3,500 or more mites.
It has been estimated that a typical used mattress contains form 100,000 to 10 million house dust mites within it. Mite development in carpet on slab floors and floors over cool crawl spaces and basements is probably additionally slowed because of the cooler temperature. The highly desiccation-resistant, prolonged quiescent protonymph is thought to be the stage which survives the dry conditions of the winter heating season and is the source of mites for population growth during the favorable periods which follow. House dust mites can be easily dispersed within a house and even outside. For instance, marked mites ere traced from a couch via clothing tot he rest of the house and the family vehicle within a 2 week period.
Control
The best control method presently available is habitat removal coupled with sanitation and moisture control. Habitat removal consist of encasing the mattress and pillows in special plastic bags with zippers to separate the sleeper from the mites. Remove carpeting and drapes from the bedroom. In the rest of the house, remove stuffed or cloth-covered furniture, carpeting, and drapes wherever possible. Vacuuming should be done with a HEPA-filter equipped vacuum which removes particles down to 0.3 microns in diameter. Vacuuming alone is not the solution because, for instance, it removes only about 7% of the mites from carpeting.
Clean window coverings every 2 weeks. Hot water and steam carpeting, with or without various solutions, is not advisable. Send area rugs out to be dry cleaned when soiled. Lower the relative humidity to less than 45%. Having a dog as a pet is like adding another person to the household. This is apparently not true for cats. There is one acarcide currently labeled for house dust mites, but it is not labeled for application to bedding. This is benzol benzolate and it requires repeated applications. Remember that bedding is the prime harborage area with stuffed furniture being a close second, and carpeting is of much less significance.