224 PROCEEDINGS OF THE NATIONAL MUSEUM VOL. loS 



fossorial — v.hich sharpened the suspicion aroused by the morpho- 

 logical differences between these forms. As a result, Euschon- 

 gastia sp. is being held for further study. 



In addition to the host record of a chigger, it is important to 

 systematics to know as much as possible of the nature of the 

 host-parasite relationship. It has been indicated that the separate 

 ecologies of the host and the chigger must somewhere coincide. 

 The systematist is better able to evaluate the host record if he 

 knows to what degree a chigger is host-specific and to what degree 

 its ecology assists or prevents its meeting certain hosts. Wharton 

 (1946) working with E. indica on Guam, found the free-living 

 stages in the arboreal nests of Rattus mindanensis. These rats 

 were the only hosts found to be parasitized by the chiggers. 

 Largely on the basis of previous experience with E. indica, 

 Wharton inclined to the opinion that proximity was the more im- 

 portant factor in this parasitism. However, he was unable ex- 

 perimentally to infest Rattus exulans and Mus musculus — two 

 ground-dwelling rodents found in the area — as well as guinea 

 pigs and chickens. He did infest Rattus mindanensis. From these 

 results he felt that host distribution was conditioned also by 

 peculiarities of host and parasite. Lawrence (1949) was unable to 

 affirm host-specificity for African trombiculids on mammals. He 

 stated that some appeared to be host-specific, but this could have 

 been the result of too few collections. In the present investiga- 

 tions only E. peromysci was used experimentally. E. peromysci 

 has a wide range of hosts. Its lack of host specificity was con- 

 firmed in the laboratory. It attached to the skin of a man. It 

 engorged on white mice. Further, no species of Euschongastia 

 which has been collected a number of times has been found 

 specific for a single host species. From this it seems quite possible 

 that apparent host preference is but the reflection of the ecology 

 of the free-living stages which places the chiggers in close spatial 

 relationship with particular hosts. 



However, as Wharton (1946) found, certain peculiarities of 

 chigger and host may influence distribution. E. blarinae, for 

 which a fairly long host record is available, seems to have a host 

 preference for shrews. In Duke Forest unattached E. blarinae 

 was collected — although never in large numbers — in combination 

 with E. peromysci, which commonly attaches to Peromyscus leu- 

 copus. The sites were obviously available to P. leucopus. Yet, no 

 E. blarinae was collected from this mouse. Also, the ubiquitous 

 and nonhost-specific E. peromysci, found abundantly on Pero- 

 myscus leucopuis in Duke Forest, was not taken from shrews in 



