74 
NOTES ON THE DISEASES OF THE CHINCH BUG.* 
The fact that the almost total disappearance in 1889 of a 
great outbreak of the chinch bug which had cost Illinois and 
adjacent States many millions of dollars was apparently due 
chiefly, if not altogether, to parasitism by fungi, or, in other 
words, to contagious insect disease, has given to these diseases 
of insects a very special interest and importance at the present 
time; and possibly successful attempts made in Minnesota, Kan¬ 
sas. and Indiana for the transfer of one of them to previously 
healthy bugs, and even for its dissemination in some instances 
to fields previously free from them, gives to researches bearing 
on this subject a great and permanent practical value. The 
time consequently seems opportune for a fuller report than I 
have hitherto made on some points of my own work on the 
diseases of the chinch bug,—a work begun in 1882, and continued, 
as opportunity and material could be had, up to the present 
time. 
We have at present positive knowledge of two diseases of the 
chinch bug and highly probable evidence of a third, the first 
two associated with the occurrence of spore-bearing fungi (Ento- 
mophthora and Sporotrichum), and the third with a bacterial 
species described in 1883 as Micrococcus insectoruin. In the first 
and last cases we lack the absolute certainty given by experi¬ 
mental transfer of the disease by means of its characteristic 
fungi to insects shown to be previously free from it; but with 
respect to the first of these affections, that connected with the 
Entomophthora, this deficiency lias little meaning. The specie? 
of this genus are so generally parasitic on insects, and the nature 
of their effect upon the chinch bug is so unmistakable, that ex¬ 
perimental evidence is really quite unessential. The subject ol 
the bacterial diseases is, however,, a much more difficult and in 
tricate one, and positive assumption of the pathogenic charactei 
of any given microbe is always unwarranted unless brought tc 
the test of precise transfer experiments. 
The evidence in favor of a bacterial disease of the chinch bug 
is essentially as follows: 
First, the very general occurrence of vast numbers of a single 
species of Micrococcus in the ceeca of the alimentary canal oi 
chinch bugs evidently suffering from disease, accompanied by the 
complete destruction of the epithelium of such cceca, at a time 
when an enormous mortality was apparent among them: sec 
ond, the absence of such bacterial affection duriflg periods ol 
normal prosperity; third, a variation, generally speaking, i n the 
* This article has been revised in passing through the press to include results arrivec 
at here since it was written, and it is now substantially complete to June lo.iWi. 
