20 INSECT PESTS OF FARM, GARDEN AND ORCHARD 



mon as formerly, and little reflection will show that these scourges 

 are entirely due to natural causes. In fact they are very largely 

 brought about by man himself. Some of these pests are due to the 

 fact that in trying to subdue nature by clearing and cultivating the 

 land, man has deprived the insects of their natural food plants. 

 They must, therefore, needs feed upon that which is substituted 

 by him, and as it is less abundant than the former wild vegeta- 

 tion, the number of insects and the injury they inflict are more 

 apparent. 



By far the larger number of our worst pests, however, are those 

 which come to us from foreign shores. Foreign insects are con- 

 stantly being imported in one way or another, sometimes being 

 already established pests in other lands and sometimes only becom- 

 ing so under their new surroundings. These are even more injuri- 

 ous than those native, for whereas many of our native birds, in- 

 sects, and diseases constantly prey upon native insects and thus 

 keep their numbers in check, the enemies of imported pests rarely 

 accompany them, and they thus increase at an alarming rate and 

 do enormous damage before they are attacked by the natural 

 enemies of similar native pests. It is in the case of these imported 

 pests that the value of parasitic and predaceous insects is most 

 apparent. In an effort to make use of them to fight the gypsy 

 and brown-tail moths in New England, the U. S. Bureau of Ento- 

 mology has for several years been importing large numbers of the 

 parasites and predaceous enemies of these pests and liberating 

 them in affected regions, thus carrying on a practical experiment 

 on a large scale which may show the importance of these parasites 

 in combating imported pests. 



Even with o.ur native pests, however, we have frequent exam- 

 ples of the value of parasitic and predaceous enemies. Thus the 

 southern grain louse, or "green bug," was soon brought under 

 control by the myriads of little parasites which preyed upon it 

 (see page 155), and these were artificially transported for some 

 distance and liberated in large numbers. Though these efforts at 

 the distribution of this parasite may be open to some question 

 as to their effectiveness, other parasites have been successfully 



