94 
7. The fungus producing this disease will start rarely, if at 
all, on dead chinch-bugs, if we may judge from the results of sev¬ 
eral experiments made this summer. (See Nos. 37-40 and Nos. 
46-47. ) Wherever a dead chinch-bug shows the fungus in the 
field, it is therefore probable that it was infected when alive. Some 
doubt is thrown upon this conclusion, however, by the fact that 
upon dead soft-bodied insects, like cabbage worms, the Sporotrichum 
grew as promptly and luxuriantly as upon the insects infected 
while alive. (See Nos. 21-27 and 41.) 
8. The resistant power of healthy chinch-bugs exposed t) in¬ 
fection is well shown by the fact that thousands of bugs, young 
and old, have commonly lived for many days, and even for several 
weeks, moulting, maturing, copulating, and laying their eggs, when 
shut up in contagion boxes which had been heavily stocked with 
fungus spores from dead insects, aad had been made in every way 
as favorable as possible to the development of the disease. The 
percentage of those that would succumb, from day to day, was 
often ridiculously small. (See Nos. 6S-71). On the other hand, 
it is probable that the heavy pressure upon the office for a supply 
of infected chinch-bugs frequently induced the. too early and com¬ 
plete removil of the bugs from such boxes, thus retarding the de¬ 
velopment of the fungus among the imprisoned insects. 
9. The growth of the fungus in such boxes is sometimes checked 
and the whole experiment brought to a standstill by the appear¬ 
ance in the boxes of minute mites (apparently brought in with 
the food supplied to the bugs), which multiply in the boxes and 
greedily devour the fungus of white muscardine as fast as it 
grows. (See No. 68, July 31, August 9, and 22; No. 69, July 30 
and August 3; No. 70, July 30 and 31 and August 2; and No. 
71, July 30.) 
These mites were repeatedly noticed by us in July, but were not 
suspected of an injurious influence on our operations until July 
30, when experiments demonstrated that they were diligently 
feeding on the growing Sporotrichum. Confined with a fungus- 
covered chinch-bug Jnly 30 at 3 p. m., they had completely cleared 
it off by the next morning. Another lot, placed uuder a glass 
with four such bugs at 9 a. m., had eaten up the last vestige of 
the fungus by 4:30 p. m. Similar trials showed that they would 
clear away, with equal readiness, the fungous growth from a culture 
on corn-meal batter. Prolonged search of the earth outside, made 
where the supply for our contagion boxes w’as obtained, and a 
similar search of the sources of the food supply of the imprisoned 
chinch-bugs, gave us no hint of the origin of the mites. The same 
mite species was noticed August 7 in the contagiou box of a 
farmer near Tonti, in Southern Illinois, aud it seems likely that 
these mites came in with the chinch-bugs sent us from the field. 
10. Comparative experiments with fungus spores from diseased 
chinch-bugs, and with those derived from artificial cultures on corn 
meal moistened with beef broth, show that the latter are nearly, 
if not quite, as efficient agents of infection as the former. We 
used this year only cultivated spores two or three removes from 
