Stored Products Mites

from Hughes, 1976.)

higher. The dermatitis experienced by food handlers on contact with A. siro is commonly known as grocer's itch. Other names for dermatitis caused by A. siro and related mites are baker's itch, dried-fruit-mite dermatitis (Carpo-glyphus lactis, Carpoglyphidae; Fig. 23.13), wheat pollard itch (Suidasia nesbitti; family Suidasiidae), and vanillism, reflecting the product or commodity involved.

A mite closely related to A. siro that also causes human dermatitis is A.farris (Fig. 23.14). It is a widespread

FIGURE 23.13 Carpoglyphus lactis (Carpoglyphidae), male, ventral view. (Modified from Hughes, 1976.)
FIGURE 23.14 Acarusfarris (Acaridae), female, ventral view. (Modified from Hughes, 1976.)

species that has been reported to cause skin irritation to farm workers handling infested bales of hay in England (Hughes, 1976).

Another common acarid mite in stored products is the cosmopolitan Tyrophagus putrescentiae. It is particularly a problem in foods with a high protein and fat content, such as hams, cheeses, nuts, seeds, dried eggs, and fish meal. This mite feeds primarily on fungi (e.g., Aspergillus, Eurotium, Penicillium) that tend to thrive on foods stored at warm temperatures (>30° C) and relatively high humidities (>85%). Under such conditions it can complete its development from one generation to the next in 2—3 weeks. It can be a pest in mycology laboratories, where it often contaminates fungal cultures. The term mold mite is commonly used to refer to T. putrescentiae and a closely related species, T. longior (Fig. 23.15).

In the Tropics, T. putrescentiae causes a dermatosis called copra itch among workers handling copra, dried coconut kernels from which coconut oil is extracted. In Italy, human cases of cutaneous and respiratory allergies have been attributed to this mite among workers handling raw hams; the mite apparently thrives in the white dust (ruffino) that covers hams during the seasoning process (Ottoboni et al., 1989). T. putrescentiae occurs throughout much of the world, where it is found in a wide range of situations, including grasslands, soil, old hay,

FIGURE 23.15 Tyrophagus longior (Acaridae), male, dorsal view. (Modified from Hughes, 1976.)

mushrooms, and the nest of bees and ducks. This mite was reported as the cause of human dermatitis in a butcher's shop in Austria, where it was breeding in molds growing on bacon in a poorly ventilated room (Czarnecki and Kraus, 1978).

A few other acarid mites are known to cause human dermatitis. One is Tyrolichus casei, reported by Henschel (1929). This is a cosmopolitan species commonly found in stored foods, grains, flour, cheeses, dogmeal, old honey combs, and insect collections (Hughes, 1976). Another is Suidasia nesbitti, which occurs in Europe, Africa, North America, and the West Indies. Although it is particularly associated with wheat pollards and bran in England (Hughes, 1976), it also has been reported in rice, in whale meat infested with dermestid beetles, in dried bird skins, and in milking machinery.


Pyemotid mites are ectoparasites of insects that typically attack the larval stage of moths, beetles, and hymenopter-ans. A few species commonly occur in dried, insect-infested plant products such as hay, straw, and grains. On contact with humans and other animals, these mites cause intense itching when they pierce the skin with their stylet-like chelicerae and inject a toxin produced in their

FIGURE 23.16 Straw itch mite, Pyemotes tritici (Pyemotidae), gravid female, dorsal view. (From Gorham, 1991; courtesy of the US Department of Agriculture.)

salivary glands. It is a very potent neurotoxin which they use to immobilize their insect prey, enabling them to paralyze insects 150,000 times their size (Tomalski and Miller, 1991).

The most important species affecting humans is Pyemotes tritici (Fig. 23.16). It is variously known as the straw itch mite, hay itch mite, and grain itch mite, depending on the plant material with which it is associated. Exposure to P. tritici represents an occupational hazard for agricultural workers, sales and stock personnel in farm supply stores, and other individuals in the arts and crafts field who handle wheat, hay, and straw. People handling infested materials usually develop multiple skin lesions in the form of papules or papulovesicles, accompanied by intense itching. Each bite site typically consists of a minute white wheal with a central erythematous area where a tiny vesicle forms. During the early stages, the mite often is visible as a tiny white speck where the vesicle is located. Although lesions can occur on any exposed part of the body, they usually appear on the back, abdomen, and forearms, where contact with infested materials typically takes place. Lesions seldom occur on the face or hands. Heavily infested, or sensitized, individuals may experience other symptoms, including headache, fever, nausea, vomiting, diarrhea, and asthma (Southcott, 1984). Less commonly reported are chills, fever, malaise, and anorexia (Betz etal, 1982).

Two other species of Pyemotesreportedly cause human dermatitis. Several people in France developed erythematous lesions and complained of intensely itchy papules after handling dried everlasting flowers (Helichrysium angustifolium) infested with P. zwoelferi imported from Yugoslavia (Le Fichoux etal., 1980). Other people working in a food-mixing shed of a farrowing house developed a papular rash after contact with grain infested with P. berfsi in Czechoslovakia.


Cheyletid mites are mostly free-living predators that commonly feed on other mites and small arthropods in stored products. Occasionally they cause pruritic dermatitis in people handling infested grains and other dried plant materials. The most common cheyletid found in stored products is Cheyletus eruditus. This cosmopolitan species has been used commercially as a biological control agent to reduce the numbers of grain mites, notably Acarus siro and Lepidoglyphm destructor, in granaries and agricultural warehouses. Severe pruritus was reported in a worker at a wholesale florist shop handling fern wreaths imported to the United States from the Philippines {Shelley et al., 1985). The mite involved was apparently C. malaccen-sis, a species previously shown to cause itching papules in humans (Yashikawa et ai, 1983). A second cheyletid mite, Cheyletomorpba lepidopterorum, also may have been involved.

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