44 Contagious Diseases of the Chinch-bug. 
are present. These conditions we do not know exactly, but it 
is probable that the following tend to promote epidemics : 
1. Humidity, resulting — 
(a) From sufficient rain or cloudy weather. 
(6) From conditions of soil or surrounding vegetation which tend to retain 
moisture. 
2. Increased susceptibility of insects to diseases. This pos- 
sibly may come about — 
(a) From exhaustion after breeding, laying of eggs, etc., and the weakening 
of the insect at old age. 
(6) From the weakening effect of unfavorable meteorological conditions. 
(c) From the effect of other diseases or pathological conditions of some kind. 
C. 
1. It is more than probable that Sporotrichum is always 
present to a greater or less extent in any locality, and that the 
amount of it depends primarily upon the number of chinch-bugs 
and the condition of the weather. 
2. Since dry weather favors the multiplication of the chinch- 
bug and is detrimental to the development of Sporotrichum, the 
assumption seems reasonable that a series of dry years would 
result in an increase of chinch-bugs without a corresponding 
increase of Sporotrichum. 
3. In such an event we would conclude that the artificial in- 
troduction of Sporotrichum would result in the destruction of 
more bugs than would naturally occur. 
4. Finally, with these considerations, we suggest that it is 
best for the farmer to see that the diseases are present in his 
fields, so that if favorable conditions arise, an epidemic may re- 
sult; but it is not wise to put entire dependence on infectious 
diseases, for it is uncertain whether these conditions may arise, 
or, if they do, whether they may be in time to materially aid 
the crops. 
IX.— THE BARRIER METHOD. 
The habit of chinch-bugs of leaving the small-grain fields in 
a body about harvest-time, and migrating to the corn-fields, 
where they literally blacken the first few rows, is too well known 
by farmers to dwell upon. The bugs go on foot in’these migra- 
tions, and the winged ones are seldom known to fly. At such 
times it is possible to trap and destroy the bugs almost utterly. 
~~ . =a 
