46 



from year to year. When man came in and cut 

 down the forest or plowed up the prairie the natural 

 food plants of these insects were destroyed and they 

 were compelled to perish or feed upon the plants 

 to which these areas were then devoted. Many of 

 these inhabitants of forest and fields perished when 

 their host plants were destroyed, but many others, 

 more hardy in their character, succeeded in adapt- 

 ing themselves to the new conditions and have 

 become serious pests of the cultivated crops. The 

 destruction of the forest also destroyed the natural 

 enemies of the pests now troubling us as well as 

 their food supply. In the interchange of commerce 

 between different countries new insects and diseases 

 are being constantly exchanged, some of which find 

 the new conditions even better adapted to their 

 development than the old. In many cases their 

 natural enemies have been left behind and they 

 enjoy a period of unrestrained development under 

 their new environment and become exceedingly 

 annoying and destructive. 



Another factor deserving of special emphasis in 

 this connection is that cultivation always presents 

 large areas of food plants to these organisms and 

 nothing so stimulates their development as an 

 abundant food supply. In the days when gardens 

 were far apart and comparatively small there was 

 little opportunity for the common garden pests of 

 the day to spread from garden to garden and from 

 section to section. But at the present time when 

 even the home gardens are much closer together, 

 and in the vicinity of the larger cities where the 

 commercial gardens extend almost unbroken over 

 hundreds and even thousands of acres, it is a com- 

 paratively easy thing for these organisms, stim- 



