THE GENUS TROMBICULA BERLESE, IN AMERICA 

 AND THE ORIENT. 



By H. E. EwiNG, 



Bureau of Entomology, U. S. Department of Agriculture, 



Washington, D. C. 



The recent demonstration that the well-known "kedani," 

 or chigger mite of Japan, is the active agent in the transmission 

 of a deadly human disease ("tsutsugamushi" disease, or flood 

 fever) has brought the whole chigger mite group under the 

 suspicion of being one of possibly great importance in the 

 carrying of disease among man and domesticated animals. 

 The further rearing of the adults of this chigger in 1916 by two 

 groups of Japanese workers, and proving them to be Trombi- 

 culas has paved the way for an investigation into the taxonomy 

 and biology of all the species of this genus. Such an investiga- 

 tion is now of prime importance, for we may well presume that 

 the other species of the group are not so vastly different in their 

 habits from those of the deadly "kedani." 



During the summer of 1919 the writer had the good fortune 

 to meet Dr. M. Miyajima and to study with him some of the 

 different members of the genus. At first it appeared to us that 

 our only described species, Trombicula splendens Ewing, was a 

 synonym of the Japanese form, the adult of the "kedani," 

 which Dr. Miyajima holds to be Trombicula coarctata Berlese. 

 A more careful study of the type of T. splendens, as well as the 

 paratypes in the American Museum of Natural History, has 

 shown that the two species are quite distinct, as will be made 

 evident in this paper. While Dr. Miyajima was yet in this 

 country another Trombicula species was discovered by the 

 writer near Washington, D. C. This species is described in 

 the present paper for the first time. 



When examined superficially all the known species of the 

 genus Trombicula appear remarkably alike. They vary in 

 length from 1 to 1.6 mm. in most cases and are always well 

 clothed with strongly pectinate setae. The color varies from 

 that of human flesh to a scarlet vermilion, but usually would 

 be called a reddish orange. Their proportions are almost 

 identical; legs moderate, body stout, cephalothorax small, the 

 abdomen deeply constricted; this latter character at once 

 distinguishing them from all other Trombidiidae. 



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