OTHER ENEMIES OF MAN 



227 



internal poison such as Paris green or lead arsenate 

 may be sprayed on the leaves. However, an insect 

 such as the chinch bug, which secures its nourishment 

 by sucking plant juices, cannot be controlled by in- 

 ternal poisons. Sucking and boring insects are con- 

 trolled by the use of some type of spray which will 

 be absorbed through the outer covering of the body 

 and thus kill them or by one which will clog up the 

 spiracles, or breathing pores, and kill them by suffo- 

 cation. Sprays of this sort commonly used are whale 

 oil, soap, nicotine, and sulphur mixtures. 



Traps. In a few instances some control over an in- 

 jurious insect has been effected by the construction of 

 traps of one sort or another. In Kansas the migration 

 of chinch bugs has been controlled by the construc- 

 tion of post-hole traps. A barrier of creosote, which 



U. S. Deft, of Agriculture, Bureau of Entomology and Plant Quarantine 



FIG. 359. POSTHOLE TRAPS USED IN THE CONTROL OF THE 

 CHINCH BUG 



the chinch bug dislikes, is placed along an infested 

 field. The bugs do not cross the barrier, but follow 

 along it. At intervals these creosote barriers empty 

 into post holes. The insects go into the hole and are 

 destroyed by a suitable poison. See Figure 359. 



Crop rotation and altered, planting. Some insect pests 

 feed only upon a single crop. In such cases, alternat- 

 ing this crop with one upon which the pest does not 

 feed tends to starve out the insect and thus reduce its 

 numbers materially. This method is used with con- 

 siderable effectiveness in the control of the cotton-boll 

 weevil in the South. Fields upon which cotton is 

 grown one year are either left idle or planted to an- 

 other crop the following year. 



Knowing when an insect will appear to feed upon 

 a given crop often proves helpful in protecting the 

 crop. The planting of the crop may be either advanced 

 or delayed so that it will mature before or after the ap- 



pearance of the insect. Corn is frequently planted late 

 to avoid the corn borer. Also some types of wheat, if 

 planted late, avoid attacks by the Hessian fly. 



Dusting. This method of control of insects is closely 

 related to spraying. It consists of dusting the poison 

 on the plant in the form of a fine powder. Both inter- 

 nal and contact poisons may be applied by this 

 method. In recent years dusting cotton fields with cal- 



U. S. Dept. of Agriculture, Bureau of Entomology and Plant Quarantine 



FIG. 360. DUSTING A FIELD OF COTTON WITH CALCIUM ARSENATE FOR 

 THE BOLL WEEVIL 



cium arsenate by means of airplanes has proved effec- 

 tive in the control of the boll weevil. 



Plowing under and burning over. In some instances 

 such as in the case of the European corn borer, the in- 

 sect may live through the winter in the stubble which 

 is left in the field after the crop has been harvested. 

 Fall plowing of s'uch fields or burning them over may 

 greatly reduce the numbers of insects appearing in 

 the spring. 



Quarantine. After an insect pest has gained a start 

 in a certain section of the country, it is important that 

 it be prevented from spreading to other parts. To ac- 

 complish this purpose quarantine areas are often es- 

 tablished. Patrols are placed along the highways to 

 stop all vehicles leaving the infested area and to at- 

 tempt to prevent the transportation of any materials 

 across the line which might carry the insect in any 

 stage of its life cycle. 



The fight that man is carrying on to protect his 

 crops and other resources from the ravages of insect 

 pests is so important to every one that you should 

 become familiar with some of the worst pests so that 

 if the opportunity presents itself, you may engage in 

 the war to exterminate them. As has been said, effec- 

 tive control can be brought about only when the life 

 histories and habits of the pests are thoroughly under- 

 stood. 



Exercise. Make an investigation in order to learn 

 of the injurious insects and plant diseases at work on 

 trees, shrubs, flowering plants, and crops in your com- 

 munity. Learn which methods of control ore used and 



