SOME INSECTS AT WORK ON FARM CROPS 269 



Fig. 108. A leaf-devouring caterpillar 

 (Acronycla) 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 f ig . 109. a sucking insect: the 

 beaks and suck out the plant juices £lSj weed bug < - 0nco ^ Uus , 



