INSECTS INJURIOUS TO SMALL GRAINS 



139 



when about seven days old, so the numbers of the pest obviously 

 increase with enormous rapidity, and with thousands of tiny beaks 

 pumping out the sap the young grain plants soon succumb. The 

 rate of reproduction and growth is, of course, much slower in 

 colder weather, the above being the average for the growing season. 

 Thus in an open winter the aphids will continue to multiply, and 

 by February, in northern Texas, small spots of wheat and oats 

 will show the effect of their work, by March the injury may become 

 widespread and serious, and by the middle of April the crops may 

 be ruined. As the aphids become excessively abundant and the 



FIG. 119. Toxoptera graminum: a, newly born, and 6, adult wingless green 

 bug, greatly enlarged. (After S. J. Hunter.) 



food supply disappears, almost all develop wings, and immense 

 clouds of the winged females are carried northward by the 

 winds, so that an outbreak in early spring in the South leads to an 

 infestation farther north, and excessive multiplication will again 

 carry the pest still northward, progressing in that direction as it 

 increases during the season, rather than being spread at one time. 

 Thus in 1907 it became abundant in Oklahoma in April, in Kansas 

 in May, and by July it was found in Minnesota, where it rarely 

 occurs and does no damage. With the maturing of wheat and oats 



