112 



EEPORT 108^ U. S. DEPARTMENT OF AGEICULTURE. 



but holding that the hypopus ^vas a natural stage in the development of most if not 

 all twogh-phi. 



From an economic standpoint the Tyrogh-phidae 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 t\Togh-phids would in- 

 clude cheese, flom", sugar, hams, dried meats, hair in furniture, mattresses and pillows, 



Fig. 233. — Labidophoms sci- 

 unnus: Male. (Original.) 



Fig. 23i.— Carpogltjphus passularum: Male. 

 (Author's illustration.) 



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 ne§ts, scale 

 insects, pinned insects of the entomologist's collection, and even the human cor]>se. 

 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 Monicziella do some good by 

 feeding on scale insects. The "bulb mite" or "Eucharis mite," Rhizoglyphus 

 hjacinthi Boisd., has long been a prominent enemy to hothouse cultivation. It bur- 

 rows 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 steins of carnations. Still another Rhizoglyphus 

 has been found to eat through the grafting wax on grafted i)lan ts, bore beneath the 

 bark, and thus prevent the union of graft and stock. The mushroom mites, both in 



