April, ’18] 
EWING AND HARTZELL: CHIGGER-MITES 
263 
by Riley, in 1868, on the Rocky Mountain locust. The following 
year it was reported from Oregon and Missouri. In May, 1874, the 
adult was observed attacking the eggs of the Rocky Mountain locust 
in northwestern Iowa. It was recognized by Riley as Trombidium 
sericeum Say. At that time the immature stages of the Trombidiid^e 
were unknown. In the same report he recognized the larval form, of 
what afterwards proved to be the same species as the above, as Astoma 
gryllaria LeBaron. Riley was the first to work out the life-history of 
the locust mite. In 1878 he published a description of it as a new 
•species under the name Trombidium locustarium. Banks, however, 
considers it a synonymn of Astoma locustarium Walsh. In 1912 the 
senior writer sent an adult locust mite to Berlese, who determined it 
as Euthrombidium locustarium Walsh. A larva of the same species, 
taken from Melanoplus differentalis, was sent to Dr. Oudemans, who 
recognized it as nothing less than the European Euthrombidium tri¬ 
gonum Hermann. Since Oudemans based his determination on larval 
characters, which in this group are more definite than adult characters, 
we believe it to be correct. Furthermore, we have carefully compared 
Oudeman’s and Berlese’s descriptions and figures with our own mate¬ 
rial of this species and conclude that Euthrombidium locustarium Walsh 
is synonymous with Euthrombidium trigonum Hermann. 
The larvae of the locust mite may be distinguished from the other 
members of the genus by the bifurcate coxal spurs and the four hyaline 
lobes on the cephalic border of the front dorsal shield. 
Riley was first to study the biology of this species. The senior 
writer has also carried on life-history experiments with this mite, and 
succeeded in rearing an adult from a larva infesting Melanoplus bivit- 
tatus. The adults showed a decided preference for grasshopper eggs. 
In no case could the mites be induced to attach themselves to man. 
It is also of interest to note that this mite has never been reported 
from man or domestic animals in Europe. 
As far as is known the hosts of the locust mite are confined to four 
families of Orthoptera, namely: Acridiid^e, Locustid.e, GryllidvE 
and Mantid^e. It has been found on the following species of grass¬ 
hoppers in this country: Melanoplus differentialis, M. spretus, M. 
augustipennis , Spharagemon bolli, Schistocerca americana. 
Euthrombidium trigonum is generally distributed throughout Min¬ 
nesota, South Dakota, Iowa and Illinois. It has been reported from 
Nebraska, Kansas, Missouri and Oregon. It has also been found in 
Germany and Holland. 
