322 PRINCIPLES OF ECONOMIC ENTOMOLOGY 



with some other measures. It may be used upon dogs and 

 cats for the kilhng of fleas by dusting in the hair. 



Machinery. — For the appHcation of these various insecti- 

 cides, a great many forms of spraying outfits, dusting 

 machines, etc., have been devised. These are now so thor- 

 oughly standardized and handled by reputable firms that 

 anyone may secure such outfits as may be needed for his 

 individual purpose. 



Cultural Methods. — iVnother distinct group of measures 

 for insect control (the indirect methods) may include those 

 which have to do with methods of culture and alternation of 

 crops and ^'arious cultural methods which incidentally have 

 an effect upon the activities of insects. 



First among these may be mentioned the general practice 

 of crop rotation which for a good many insects serves in an 

 admirable way to prevent undue multiplication of injurious 

 forms. Aside from its advantages in other waj's, rotation 

 serves to dislodge or starve out a great number of insects 

 which are not able to migrate readily and which become 

 established in any field only after several years of uninter- 

 rupted development. For such forms the plowing up of the 

 fields or a change from one crop to another may prove an 

 almost perfect control. A striking example of this has been 

 noted in the case of the corn-root worm. In somewhat les- 

 ser degree the process is available for many of the pasture 

 and meadow insects which are dependent upon grasses as 

 their main food supply and which when grass is plowed 

 under, especially if this is done at a time when the insects 

 are in larval or in a known migratory stage, serves to destroy 

 them very effectively. 



In a general way plowing will cut off the food supply, some- 

 times will bury the insects to such a depth that they do not 

 extricate themselves. In this connection, however, it is some- 

 times very important that the condition of the insects be 

 known, as there are cases, such as white grubs, sod worms, 

 and wire worms, which if plowed under with the sod will, 

 if a second crop is planted soon, transfer their attack to the 

 new crop with very disastrous consequences. It frequently 



