but holding that the hypopus was a natural stage in the development of most if not all tyroglyphi. From an economic standpoint the Tyroglyphidæ are one of the most important groups of mites, but owing to their small size and pale color they have often been overlooked, and the damage accredited to some larger mite or insect that happened to be in the material. By their rapidity in breeding they make up for their minute size, so that foods, such as flour and sugar, are often so badly infested that the whole mass of the substance appears to be in motion. Dried fruits, dried meats, and grain in mills are, perhaps, most seriously affected by them. Their frequency in cheese and sugar has won them the names of "cheese mites" and "sugar mites," while the disease known as "grocer's itch" is due to their presence on the hands of persons handling infested products. A list of materials attacked by tyroglyphids would include cheese, flour, sugar, hams, dried meats, hair in furniture, mattresses and pillows, FIG. 233.-Labidophorus sci- FIG. 234.-Carpoglyphus passularum: Male. grain in mills, cereal foods, many drugs, wine, dried fruits, jams and jellies, seeds of many kinds, bulbs, roots of plants, mushrooms, feathers, hay, refuse in nests, scale insects, pinned insects of the entomologist's collection, and even the human corpse. Some species are, however, of little economic interest and occur in the nests of mice, moles, and ants, in decaying bark of trees, in sap from wounds in trees, and a few are attached to certain insects. The species of Monieziella do some good by feeding on scale insects. The "bulb mite" or "Eucharis mite," Rhizoglyphus hyacinthi Boisd., has long been a prominent enemy to hothouse cultivation. It burrows into the healthy tissue of bulbs and roots, thus giving entrance to destructive fungi and bacteria. This is the species infesting Bermuda lily bulbs, and it has been shown that an allied species does great damage to the roots of the vine in Europe. Another species causes injury to the stems of carnations. Still another Rhizoglyphus has been found to eat through the grafting wax on grafted plants, bore beneath the bark, and thus prevent the union of graft and stock. The mushroom mites, both in this country and in Europe, are prominent obstacles to successful mushroom culture. Cellars apparently clean in the beginning of the season may be so badly infested by Christmas that crops are impossible. It is a difficult problem to destroy tyroglyphids. Since they have no trachea, they are not very susceptible to fumigation, although some of them will succumb to prolonged treatment. Flowers of sulphur and carbolic acid are, at times, of much use; but in many cases destruction of the material attacked is the only remedy. Since many in the hypopial stage are carried by flies, it is advisable to have the windows screened in all factories where cereals, drugs, dried meats, and fruits are prepared. When very abundant the tyroglyphids are attacked by various predaceous mites, chiefly Cheyletus and Parasitus, which greatly reduce their numbers, and in some cases entirely destroy them. Various species have at different times been recorded as temporarily parasitic on man, causing itching and soreness of skin. Persons handling infested products are apt to become attacked, but the mites soon disappear, as they can not breed on the skin. Most of the Tyroglyphidæ differ but little in general appearance, and the characters that separate species are often few and minute. The family is usually considered to have affinity to the Sarcoptide and Analgesidæ, but there is more resemblance to the nymphs of the Oribatida; in fact, oribatid nymphs have been described as Tyroglyphidæ, and vice versa. The Tyroglyphide have always been kept as a separate group, either as a family, or as a subfamily of the Sarcoptide. Four groups, which may be considered subfamilies, have usually been recognized: Glyciphagus and its allies, Histiostoma, Trichotarsus, and the Tyroglyphus group. Most of the species belong to the last group. The principal genera may be recognized from the following table: 2 1. Mandibles not chelate, but elongate and toothed below; body without long hairs; palpi enlarged at tip, and provided with two divergent bristles.. Histiostoma. Mandibles chelate; palpi not enlarged at tip, not with the two bristles..... 2. Dorsal tegument more or less granular; claws very weak, almost invisible, some hairs of body plainly feathered; ventral apertures very large..Glyciphagus. Dorsal tegument not granular; claws distinct; no prominent feathered hairs; ventral apertures small.. 3. No clavate hair on base of tarsi I and II; no suture between cephalothorax and abdomen; no sucking genital disks; tarsi long. A clavate or thickened hair on base of tarsi I and II.. 4. Body without bristles; tarsi without long apical hair, but one at tip of preceding joint; a medial frontal projection over mouth parts; genital opening large, penis slender, curved... 3 Chortoglyphus. Body with bristles, no long bristle at tip of penultimate joint of legs.. 5. Legs with spines; abdomen very bristly above... Legs without spines; living on bees or in their nests. 5 .Hericia. Trichotarsus. 6. The bristle on penultimate joint of legs arises from near the middle; no suture between cephalothorax and abdomen... Carpoglyphus. The bristle on penultimate joint of legs arises from near the tip; a suture between cephalothorax and abdomen... 7 7. Cephalothorax with four distinct and long bristles in a transverse row above; tarsi I and II about twice as long as the preceding joint.... Tyroglyphus. Cephalothorax with but two long, distinct bristles (besides the frontal pair), but sometimes a very minute intermediate pair; tarsi I and II often short... 8. Tarsi with some stout spines; caroncle absent. Tarsi without spines; caroncle present.. Monieziella. 9. Body very slender; the hind pairs of legs about their length behind the front pairs.... Histiogaster. Body robust; the hind pairs of legs but little beyond the front pairs..Rhizoglyphus. The hypopi of the various genera, as far as known, can be separated by the following table: 1. A pair of clasping organs on venter near tip of body, margins not sharpedged..... No clasping organs, but an area of suckers... 2. Anterior legs end in very large claw; margins of body not sharp-edged.. Trichotarsus. Claws small or of normal size.. Labidophorus. 2 3 3. An eyelike spot each side of anterior part of body.. No such eyelike spots..... Histiogaster. 4 5. Legs very slender, especially the tarsi; hind legs often bent forward.. Histiostoma. Legs much shorter, the tarsi not slender.. 4. Venter behind with a submarginal crescentic plate; tarsi rather long.. Hericia. No such crescentic plate... 5 6 6. Five pairs of suckers in the plate arranged 2-2-4-2. Suckers not in such arrangement.. Aleurobius. .Rhizoglyphus and Tyroglyphus. b FIG. 235.-Aleurobius farinae: a, Venter of male; b, leg I of male; c, palpus, d, tarsus IV of male. (Author's illustration.) FIG. 236.- Tyroglyphus lintneri: Female. (Author's illustration.) About five species of Histiostoma are known from the United States. They differ in length of legs and in shape of body. Some occur among dead leaves, others under bark with decaying matter. Their hypopi are often very abundant and have very slender legs. The hypopial stage of one (H. muscarum Koch) is often attached to house flies; another species, H. americanum Banks (figs. 229, 230, 231), was taken under bark, which was also infested with a Rhizoglyphus. This species has a number of humps on the dorsum of the body, and upon the summit of each is a small hair. In Europe one species lives in mushrooms and spreads a disease that causes the decay of the pileus. Nearly all the species occur in decaying material, but Jensen has recorded that one species (H. berghi Jensen) lives parasitically in the egg capsule of a horse-leech in Denmark. From the egg hatches the six-legged larva, which soon molts into the nymph. The latter devours the embryonic leech and then passes into a hypopus. This escapes from the capsule, attaches itself to an insect, and, on reaching suitable locality, molts into a full-grown nymph. The latter cuts through the capsule, enters, and there transforms to the adult mite. Here reproduction takes place, and the life cycle begins anew. One species, H. tarsalis Banks, has been found in the nests of rats in California, and the hypopial form attached to the rat. fleas. The genus Glyciphagus does not appear to be as common in this country as in Europe; possibly owing to their minute size they have not been collected. A few species, of rather modest appearance, are known to me. One (fig. 232) has long plumose hairs on the body, and was found in seeds. In Europe several species appear to be common in houses and other buildings. Some species are provided with many broad scalelike hairs. In all the forms the skin is finely granulate, which character serves to distinguish it from all other tyroglyphids. The original species of the genus (as indicated by the name) and some others have been found in sugar. The mites sometimes spread to the hands of those handling such materials, and produce a skin disease known as "grocer's itch." Michael has described two remarkable forms which he discovered in the nest of the mole. The body is broad, flat, and the margins crenulate and FIG. 237.-Rhizoglyphus rhizophagus. (Author's illustration.) FIG. 238.-Rhizoglyphus hyacinthi, side view. (Original.) provided with spines. They do not occur in deserted nests, but their relation to the mole is unknown. They may, perhaps, form a distinct genus. The curious genus Labidophorus (fig. 233) has not been found in this country. The genus was based on a hypopus that is found attached to moles. Michael has worked out its life history, finding that the adult is much like Glyciphagus. The male has several curious comblike projections from the under side of the first and second pairs of legs and some plumose bristles on the other legs. The adult lives in the nests of moles. Another species occurs in the nests of squirrels and also on the squirrel. Chortoglyphus is known from but one species in this country, C. gracilipes Banks, which was found in tobacco infested by the cigarette beetle. The European species has been taken from old hay. Tyroglyphus, the typical genus, is known in this country by 9 or 10 species, 3 of which are very common. One, a species in grain and stored foods, is T. americanus Banks. Another common species is the mushroom mite, T. lintneri Osborn (fig. 236), which is very close to the European T. longior Gervais, but having the bristles smooth. This species at times is very destructive to cultivated mushrooms, and once in a bed it is very difficult to eradicate it. Busck has given an account of experiments against it which serve to show the difficulty of dealing with the pest. Severely infested beds should be destroyed, and perhaps if the earth was steam heated (as is done for rootworms) the eggs would be killed. T. longior has the long hairs of the body distinctly plumose; it has been found in great abundance in barns and mills in Canada and the Northern States. Two species, T. breviceps Banks and T. armipes Banks, have been taken from the dead larvæ of insects, and several species have been found in ant nests. Dr. Felt has described a species, T. heteromorphus Felt, which caused injuries to the stems of carnations grown in greenhouses, and the same species occurs in other decaying vegetable matter. The third pair of legs are enlarged in the male. The genus Aleurobius has been used for a species of Tyroglyphus, T. farinæ De Geer (fig. 235), the male of which has enlarged front legs. This species appears to be well-nigh cosmopolitan and is most commonly found in flour, grain, and stored foods. The great enlargement of the anterior legs of the male is a unique character in the family. The body has a few rather short hairs. Cleanliness, window screens, and frequent handling of the grain will be the best preventives for the protection of mills against this pest. Fumigation with hydrocyanic-acid gas is the best remedy, but it may be necessary to repeat the treatment several times, as it is a difficult matter to destroy these mites. FIG. 239.-Monieziella sp.: Female. (Author's illustration.) The genus Monieziella (figs. 239–241) contains species that are predaceous on scale insects. Three species are known from this country, two on Aspidiotus and one on Mytilaspis scales. It is not certain whether they feed on the living scale insects or only upon the dead ones, but it is probable that they do both. They are fairly common and undoubtedly do much good in checking the increase of these pests. To the genus Rhizoglyphus belong a number of species, found on the ground, in decaying matter, on roots of plants, and in bulbs. The body is slightly more pyriform than in most tyroglyphids, and the species are of rather large size. We have several species in the United States. One of them is the R. hyacinthi Boisduval (fig. 238) (R. echinopus Fumouze and Robin). This is the "bulb mite" or "Eucharis mite" of the horticulturists and is responsible for an enormous amount of damage. It burrows into healthy tissue, thereby giving entrance to destructive fungi and bacteria. It is especially common in hothouses, where its ravages on orchids have long been known. No one appears to have found a successful treatment. The best way is to burn the affected bulbs as soon as discovered. Some growers, however, secure good results by the following treatment: The soil of the pots of infested plants is allowed to become dry; then the bulbs are taken out and washed in a solution of tobacco water and soft soap, with a small amount of washing soda. Then they are sprinkled with freshly slaked lime and left for two days. Then they are washed with the same solution as before, to which a little petroleum has been added. They are then repotted and often do well. Mr. Woods has shown that this mite, when infesting Bermuda lilies, can not be destroyed, but much good is accomplished by the use of commercial fertilizers and rotation of crops. R. rhizophagus Banks (fig. 237) is a similar form. |