21 
Mr. Wildermuth, of the Bureau of Entomology, made a number of 
experiments. In no case was he able to provoke an attack from 
these red mites, probably Tydeus sp., even when they were confined 
upon the skin of his bare arm. On the other hand, examinations of 
straw from various points in Ohio and Indiana have revealed the 
presenco of Pediculoides in: the cells occupied by the jointworm. 
This seems to entirely eliminate ‘‘chiggers” from these investigations 
because these were probably not present and there does not longer 
appear to be any doubt that Pediculoides ventricosus is to be charged 
with causing the epidemic of this dermatitis. The cause of its own 
excessive abundance lies in the outbreaks of the Angoumois grain 
moth upon the grain in the East and the jointworm in the wheat straw 
in the Middle West. Therefore ‘chiggers”’ do not appear to figure as 
a cause in such epidemics. 
LIGHT THROWN UPON OTHER PROBLEMS. 
These investigations have illustrated very nicely the extent to 
which the solution of one entomological problem will at the same 
time also solve other problems more or less closely allied to the orig- 
inal one. The light thrown upon the cases of eruption noted by 
Doctor Harris in connection with the barley jointworm has already 
been explained. The present outbreak of the jointworm in the Ohio 
Valley probably originated in the upper Shenandoah Valley of Vir- 
ginia, extending northward and westward throughout West Virginia 
and eastern Ohio. When investigation of the insect was taken up in 
1904 a parasite, Ditropinotus aureoviridis Crawford, was also noted in 
excessive abundance, but for some reason it did not overcome the joint- 
worm. This phenomenon has been noted continually. Since that 
time it has been a perpetual enigma to the writer why it was that with 
such an abundance of its natural enemies the jointworm should con- 
tinue to spread and increase in destructiveness. Now, however, that 
we know that this predaceous mite is able to develop through a series of 
years insuchimmense numbers in connection with the jomtworm, the 
matter comes nearer a solution. Ditropinotus, as well as some other 
parasitic enemies of the jointworm, emerge in early July from eggs that 
were previously placed in the cells occupied by the jointworm. As 
soon as the adult parasites emerge they at once oviposit in cells con- 
taining jointworm larve of the same generation from which they 
themselves developed. The puncturing of these cells by the ovi- 
positor of these parasites, particularly Ditropinotus, opens a way for 
the entrance of this microscopic mite, and, once inside of the cell, 
it will destroy everything therein, whether it be jointworm or para- 
site. Thus the predaceous mite has prevented the other parasites 
from controlling the jointworm because it has continually checked 
the increase of other parasites. 
[Cir, 118] 
