58 INSECTS AND HUMAN WELFARE 



a field is to be planted to corn, few grubs will be present in 

 the cornfield. As the beetles require two years for their life 

 cycle, appearing most abundantly in alternate years, the 

 crop rotation can be planned in relation to the insects. 



The growing of substitute crops is practically this method 

 applied in a somewhat different way, and has tne further 

 advantage that the original crop is not removed to a distance, 

 but is more or less completely eliminated. This is a rather 

 fundamental agricultural change and it must be taken for 

 granted also that a substitute is something less desirable. As 

 some of us have become rather enthusiastic over substitute 

 foods during the past few years, it may be of interest to point 

 out that two potato substitutes, the dasheen in the South 

 and edible sunflower root or "Jerusalem artichoke" in the 

 North are plants which appear to be, for the present at least, 

 not severely affected by insects, and for this reason at least are 

 worthy of encouragement. 



Aside from the factors already referred to as regulating the 

 abundance and destructiveness of agricultural insects, va- 

 rious poisons are in very general use for the control of such 

 pests. Under present conditions these are the most direct, 

 and probably the most efficient means, that can be employed 

 for the protection of many crops, although with others there 

 are apparently insuperable difficulties to the satisfactory use 

 of such insecticides. 



At the time the Colorado potato beetle began its invasion 

 of the Eastern United States agriculturists were in despair, as 

 it appeared that the cultivation of this important crop would 

 have to be abandoned almost entirely over large sections 

 of our country. However, as a result of the discovery that 

 Paris Green dusted or sprayed upon the foliage would destroy 

 the beetle grubs without injuring the plants, the potato crop 

 was harvested in spite of the beetle, and spraying for potato 

 bugs has become a commonplace occupation for all who at- 

 tempt the culture of potatoes. The substitute of other less 

 soluble arsenical compounds such as arsenate of lead has 

 rendered spraying a more effective and safer procedure, and 



