SOME INSECTS AT WORK ON FARM CROPS 269 
Fic. 108. A leaf-devouring caterpillar 
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. 
Ofinsects 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. 
CMereny de) on oution bush. 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 
beaks and suck out the plant juices 
Fico. 109. Asucking insect: the 
red milk weed bug (Oncopelius 
fasciatus). 
