22 INSECTS IX.TURIOUS TO STAPLE CROPS. 



lionseliold goods, and may be exterminated by the fumes 

 of carbon bisulfide; and five are insects affecting cattle, 

 and are combated with various washes. 



Thus only fifty are really to be considered insects of the 

 farm cro^is. Of these, three are controlled by '- ditching,'^ 

 three by mechanical means or devices, and for two of them 

 hydrocyanic acid gas is sure death, while a spray of whale- 

 oil soajD is advisable for two others, a spray of kerosene 

 emulsion for six, and of Paris green or London purple for 

 fifteen, these sprays, etc. , being used largely for orchard 

 pests, which comprise eighteen of the fifty. But for the 

 control of many of the insect pests affecting the staple 

 crops, and which are, therefore, of the greatest economic 

 im2:>ortance, we have so far been unable to devise anything 

 better than a judicious manipulation of purely natural 

 agents, and for the control of twenty-three of the fifty 

 farm insects listed, or nearly one-half, and 75 per cent of 

 those outside the orchard, such methods must be mainly 

 relied upon. 



Clean Farming. 



After a crop has been harvested, there is usually some 

 portion of it which is allowed to remain on the land. In 

 this refuse the insects peculiar to the crop often go on 

 multiplying until winter, and greater damage to the crop 

 in the following year is therefore probable. Thus the 

 Wheat Joint-worm and the Corn Stalk-borer both winter in 

 the stubble of those crops, the Potato Stalk-borer remains 

 for some time in the vines, and numerous other cases 

 might be cited. It is therefore of imj^ortance in our war- 

 fare against insect pests that the remains of a crop, 

 stubble, vines, leaves, or stumps, as it may be, should be 



