IS 
They may be otherwise divided, from the practical standpoint of 
economic utilization, into two groups; those capable of growing in 
or on living insects only, and those which may be grown artificially by 
using inanimate substances as a culture medium. The difference 
between these latter groups is especially important in practice, 
because the quantity of those parasites which cannot be artificially 
grown can only be increased by infecting living insects them¬ 
selves, while those of the other class can usually be readily 
and rapidly increased at will by the use of suitable media 
and proper culture methods. Insect and protozoan parasites and 
some of the higher parasitic fungi belong to the first of these 
classes; while bacteria and the other higher fungus parasites, in¬ 
cluding the species to which this article is devoted, belong to the 
second class —that is, to those capable of multiplication by arti¬ 
ficial methods on gelatinous and other inanimate mixtures. 
As economic entomology has hitherto been pursued almost 
wholly by mere entomologists, the insect parasites of insects have 
received by far the greater share of attention, and their protozoan 
parasites have scarcely been studied at all except in connection 
with the most destructive disease of the silkworm, commonly 
known as pebrine. The fungus parasites of insects generally, on 
the other hand, have been studied until recent years almost wholly 
by botanists, interested in them simply as plant species of pecu¬ 
liar habit and rarely pushing their studies over to the field of 
practical application. 
THE CONTAGIOUS DISEASES OF .INSECTS. 
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 of an enormously high re¬ 
productive 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 which germinate and grow on 
the living insect, thus causing it to “mildew,” as we may say, 
while it is yet alive. They start from little spores or “germs” of 
microscopic size, capable of being wafted everywhere on the light¬ 
est 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 infested creature their 
tiny rootlets and speedily kill it by feeding on its blood. O After 
the death of their host these little plants continue to grow, pene¬ 
trating 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. 
