SOME INSECTS AT WORK ON FARM CROPS 269 



PIG. 108. A leaf-devouring caterpillar 

 (A crony eta) on button-bush. 



and remain in one position. 

 Most insects appear during 

 only a portion of the season, 

 and often several different 

 insects follow one another 

 in a regular succession of 

 depredations. 



Of insects that feed openly 

 upon the crops of our fields, 

 there are two classes that 

 affect the plant tissues diff- 

 erently, and that we have 

 to deal with differently. 

 These are biting insects and 

 sucking insects. The former 



are armed with jaws, and consume the tissues of the plant: 



the latter are armed with sharp puncturing beaks, and they 



merely perforate the tissues and suck up the fluid contents. 



Biting insects are beetles and grasshoppers and cutworms 



and many large caterpillars that consume parts of plants 



bodily, and many lesser leaf-skele- 



tonizers of various groups that eat 



the soft superficial tissues, leaving 



the more solid framework of the 



leaves intact. All these are con- 



trolled by spraying or dusting suit- 



able poisons (arsenate of lead, Paris 



green, etc.) upon the surface of the 



plant,, to be eaten along with the 



plant tissues. The puncturing 



insects are bugs of various sorts and 



aphids and scale insects. These 



penetrate the epidermis with their Flo . 109. A sucking insect- the 



beaks and suck out the plant juices 



bu8 (OncopeltuS 



