CHAPTER XX 

 INSECTS, DISEASES, AND THEIR CONTROL 



Much valuable training may be gained from the study of 

 insects injurious to crops in the home and school garden. 

 For detailed discussions regarding the many insects^ their life 

 histories and methods of combating them, reference is here 

 made to special books and bulletins on these subjects (see 

 Appendix). 



Live insects may be studied and their developments traced 

 by placing them in a cage shown in figure 139. 



How Insects Feed. — There are two main types of insects 

 based on their methods of obtaining nourishment: (1) Those 

 with sucking mouth parts, such as squash bugs and scale 

 insects. (2) Those with biting mouth parts, such as potato 

 beetles and all true beetles, larvas of moths and butterflies, 

 including the cabbage " worm." 



Methods of Control. — ^Substances used in the control of 

 insects are divided into two groups: (1) Contact insecticides, 

 which kill by smothering or closing the breathing pores on the 

 bodies of the insects. These include dust materials and oils. 

 (8) Poisons, which kill by entering the stomachs of the insects 

 when they eat. 



Insects with biting mouth parts are chiefly destroyed by 

 poisonous sprays or powders on the plants which they eat. 

 Suitable poisons for this purpose are Paris gi-een and arsenate 

 of lead. 



Insects with sucking mouth parts are usually killed by 

 kerosene emulsion, lime dust or other fine powders, which enter 

 the breathing pores along the sides of the body. 



Inside Feeders. — A few insects, such as tree borers (Figs. 

 140 and 141), codling-moth and plum curculio, arc difficult 

 to kill because of feeding inside the tissue of the plant. 



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