100 PROCEEDINGS OF THE NATIONAL MUSEUM VOL. IM 



rains and pointed out the importance of their principal hosts in 

 their patchy distribution. 



Wharton (1946) found the adults of Euschongastia indica liv- 

 ing in the nests of rats in trees and on the ground. The rats were 

 parasitized by the larvae. Wharton studied the biological factors 

 of the environment and gave lists of associated organisms. 

 Jenkins (1948a) gave an account of three species of TrombicuUi 

 which affect man in the United States, with data on seasonal 

 activity, distribution, habitat preference, hosts, and life cycle 

 included. 



Cookings (1948), in giving methods for collecting free larvae 

 of T. autumnalis in the field and for recovering engorged larvae 

 from hosts, indicated the larvae reacted positively to light. Also, 

 he made observations on the vertical distribution of the adults in 

 the soil and found a correlation with temperature and rainfall. 

 Jenkins (1948b) made laboratory investigations of the reactions 

 of larvae of T. alfreddugesi and T. splendens Ewing, 1913, to 

 various physical factors. He found activity to be initiated in the 

 chiggers by disturbances in the environment. The direction of 

 movement appeared to be determined by light. The reaction was 

 positive for previously dark-conditioned larvae and negative for 

 previously light-conditioned larvae. The rate of movement was 

 determined primarily by temperature. 



Medical importance: There is considerable literature on 

 Tromhicula which attack man but veiy little on Euschongastia 

 which attack man. Floch and Abonnenc (1941) stated that E. 

 guyanensis was a parasite on man. Hoffmann (1944) described 

 E. nunezi from human hosts. Nufiez (1947) gave a full account 

 of the six cases of trombidiasis in one family from which Miss 

 Hoffmann's specimens were collected. 



Description review : The manner of describing chiggers has 

 fluctuated somewhat as different workers have stressed various 

 characters. Oudemans (1912) gave a good description of the 

 whole mite, including some of the specialized setae of the legs. 

 Later descriptions frequently were less adequate. In 1925 Ewing 

 (1925b) emphasized the palpal setae, in 1937 he emphasized the 

 dorsal setae of the body, and in 1938 he used the branches on the 

 palpal claw to separate genera. Gunther (1940) noted unusual 

 body setae. Methlagl (1927) used two foi*mulas — the convexity 

 factor and the ratio of length to width — to describe scuta, but 

 other workers have not followed his method. Womersley and 

 Heaslip (1943) introduced a series of measurements of the 



