PREVIOUS WORK ON SPECIES IN THE UNITED STATES. 7 



several circular marks or sucking disks. By means of these suckers 

 the Hypopus attaches itself to an insect or other creature, and is trans- 

 ported to another locality, where it may tind a suitable breeding place. 

 The Jlypopus is therefore a stage in the life of a tyroglyphid fitted for 

 migration. The TTypopnt<^ upon reaching a suitable locality, molts into 

 an octopod nymph, which will feed and develop into an adult raite. 

 The causes that will induce a njauph to t^ransform to a llypopus are 

 yet unknown; Megnin supposed that dryness of the air or a scarcity 

 of food were necessary causes, but Michael has shown that Jlypopi 

 are developed in the absence of these conditions, and that this stage is 

 a natural and normal means of distributing the species. The structure 

 of the llyp><>pus is characteristic for each species; but it has not yet 

 been found in all species, and in (jrlyelphagm the hypopial stage is 

 only partiallv developed, so that species should not be described from 

 this stage alone. 



In the early days of acarology llypopus stood for a separate genus, 

 allied more to Gania.m.s than to Tyroglyp/n/s. Dujardin, in 1850, con- 

 cluded that llypopus was the pupal stage of Gamasidte. As investi- 

 gation proceeded, llypopus Avas so frequently found in association with 

 Tyroglyp)hus that views were advanced as to their relationship. One 

 was that Ilyjtopus was a ferocious parasite, devouring the Tyroglyplius 

 from within; another, that llypopus was the male of Tyroiilyphns; 

 and a third, that llypopus was the real adult of certain species of 

 Tyroglyplivs. The "llypopus question"" disturbed acarologists for a 

 long time, but was finally settled by the work of Megnin and Michael, 



PREVIOUS WORK ON SPECIES OCCURRING IN THE UNITED STATES. 



The Tyroglyphidte of the United States have never been investigated 

 in a systematic manner. The principal economic species have been called 

 Tyi-ogJyplius siro OY T. loiujlor^ but without compaiison with European 

 specimens. Fitch, in his Third Report (1856), described a mite, Acarus 

 rihis, which ma}^ be a tyroglyphid. In 1868 Shinier described a mite 

 as Acarus maJus; this was interpreted b}" Riley and some Euro- 

 pean authors as a tyroglyphid, but from the description it is evidently 

 what Lignieres describes as Jleui tsarcoptes coccisugus. Riley, in 18T4, 

 described a Tyroglyp)}ius phyUo.verx as destroying the grape Phyllox- 

 era. 1 have identified as this a common species of Rhizoglyphus. 

 Riley's opinion of the predaceous habit of this species was erroneous, 

 as it undoubtedly feeds on the roots of infested plants. In 1884 Haller 

 described Tyroglyphus crassipes and T. curt us from '"Amerika." 1 

 have not recognized them, and do not know whether they were from 

 the United States or not. In 1893 Osborn described a mite infesting 

 mushrooms as Tyroglyphus Untneri. I have seen numerous specimens 



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