, 
8 Contagious Diseases of the Chinch-bug. 
INSECT DISEASES. 
Nature has many ways of checking an excessive multiplica-_ 
tion among insects; as, for instance, by periods of great cold or 
heat, by drought or flood, by a scarcity of food, by predaceous ‘ 
animals (including many carnivorous insects),or through para- 
sitism by insects, protozoa, bacteria, and fungi. Parasitism is ie 
one of the most important of all of nature’s insecticides. 
‘The contagious diseases of insects are all cases of parasitism, and are due 
most commonly to parasitic plants (bacteria and mold-like species of minute size 
and enormously high reproductive rate). Bacterial parasites commonly infest the 
insect by way of the alimentary canal, while the parasitic molds attack it from 
without. To this second class belong the several species of disease-producing 
fungi specially dealt with in this report. They may be described as minute 
molds whiah germinate and grow on the living insect, thus causing it to ‘mildew,’ 
as one may say, while it is yet alive. They start from little spores or germs of 
microscopic size, capable of being wafted everywhere on the lightest breeze, and 
sprouting on the moist surface of the chinch-bug or the cabbage-worm as grass 
seed sprouts on the soil; and as they sprout they send into the body of the in- 
fested creature their tiny rootlets, and speedily kill it by feeding on its blood. 
After the death of their host, these little plants continue to grow, penetrating 
and disorganizing the tissues of their victim, and if the air is moist they send 
tiny white threads out through the body wall, soon completely imbedding the 
insect as if in a delicate tuft of finest cotton. On these little threads new spores 
will form in unnumbered myriads, and thus the dead body becomes a center of 
contagion to healthy insects. i. 
‘The bacterial diseases of insects attack first the cellular lining of the ali- 
mentary canal and afterwards penetrate to the blood. Disturbance of the diges- 
tive functions is thus the primary difficulty, and the final result is a very rapid 
post-mortem decay of all the fluids and tissues, the body speedily becoming a filthy, — 
semi-fluid mass.’’ * 
Protozoan diseases of insects have been studied very little,” 
except in the case of the pebrine of the silkworm, which has — 
been called the most destructive of all contagious insect dis- — 
eases. Foul-brood of bees, and fiacherie, which attacks silk- 
worms, cabbage-worms, army-worms, and walnut worms, are e 
examples of bacterial diseases. The muscardine of silkworms — 
is a fungus disease, very nearly allied to the white fungus or 
Sporotrichum of the chinch-bug. This white muscardine is _ 
known to attack many other species of insects belonging to sey 
*S. A, Forbes, Nineteenth Report of State Entomologist of Illinois. I have made very fre 
use of this admirable summary of our knowledge of insect diseases. 
