INSECTS AFFECTING FIELD CROPS 493 



contend with. The insects hibernate in old corn stalks, dead 

 leaves, clumps of grass or other sheltered places in the field or 

 roadside. As soon as the grasses or grains begin to grow they 

 begin feeding on them and lay their eggs, from which the first 

 brood of young soon issues. They may do serious injury to 

 the wheat or other small grains before the crops ripen. About 

 the time the wheat is ready for harvest 

 the chinch-bugs migrate to oats or young 

 corn. Fortunately, they do not fly when 

 making these migrations, but crawl slowly 

 from field to field. The eggs from which 

 the second brood are to hatch are laid in 

 the corn. The young of this brood be- 

 come mature late in the fall and seek 

 out suitable places to hibernate. If corn 

 is not available the whole season may be 

 passed on grasses. 



Many years ago it was discovered that 

 the chinch-bugs were attacked by a 

 fungus disease that sometimes very effec- 

 tively controlled them. When infected 

 bugs are taken into the laboratory and times natural size.) 

 placed in boxes with healthy bugs, the 

 latter soon become infected. These infected bugs may then 

 be sent into the fields and placed on badly infested plants. 

 In this way the disease rapidly spreads, and when the climatic 

 conditions are right it soon destroys most of the chinch- 

 bugs in the field. But this method of control has not been 

 wholly satisfactory because in cool and dry weather the disease 

 does not spread fast enough. 



Clean culture is of prime importance. If the adult bugs 

 that are hibernating in the fields or in grasses by the roadside 

 and fences are destroyed by burning, there will be no injury 

 in the following spring. When the insects are migrating from 

 the wheat to the corn they may be effectively checked by 

 barriers of dust or coal tar. The dust barrier is made by 

 plowing and thoroughly pulverizing a narrow strip of ground 



FIG. 232. The 



