Report of State Board of IloviicuUure. 85 



In order that our readers may understand why one remedy 

 is used for one insect and not for another it 'will be necessary 

 for us to make some brief references to the structure and habits 

 of certain tj^pes. For example, the great mass of injury to 

 plants by insects falls under two heads : first, where the plant 

 itself has been eaten ; c\\\A, second, where the juices have been 

 sucked out, leaving the tissues. 



Biting insects — Insects causing injury of the first class are 

 called biting or chewing insects, familiar examples of which 

 are the beetles, grasshoppers, and caterpillars, such as the 

 cabbage worm, army worm, etc. They have well-developed 

 jaws, htted for cutting and chewing the plant. Such insects 

 can be destroyed by use of direct poisons, such as the arsen- 

 icals. When applied to the leaves or other parts of tlie plant 

 it is eaten by the insect, causing its death. 



Sucking insects — On the other hand, the second type have 

 long lance-like beaks, fitted for sucking. This class includes 

 the scale insects, plant lice, squasli bug, harlequin or terrapin 

 bug, etc. They obtain their food simply by inserting their 

 beaks into the tissues of the plants, sucking the juices from 

 within. The external application of arsenical poisons to plants 

 would have little if any effect upon this group of insects, as 

 the poisons do not enter into the cells of the plants. It is 

 necessary, therefore, to employ some other substances for 

 their destruction. To this end materials are used which will 

 act externally on the bodies of the insects, either as a caustic 

 or to smother or stifle them bvclosiu"- their breathing; organs. 

 I might say in this place that insects do not breathe through 

 their mouths, as do higher animals, but through small open- 

 ings on either side of the body, called spiracles. By spraying 

 anything of a caustic or oily nature over the body of an insect 

 these spiracles are closed and the creature is destroyed. Some- 

 times the fumes of poisonous gases are employed to suffocate 

 insects, as will be described later on. Insects are sometimes 

 repelled by obnoxious substances. 



The above remarks apply especially to insects which feed 

 upon the exterior of plants or pass the greater portion of their 

 lives in an exposed condition, where they can be readily reached 

 by one of the methods mentioned. Certain other insects, of 

 both classes, biting and sucking, are subterranean in their 

 habits, that is, they feed and live upon the roots of plants 

 below the surface of the ground. Among these the white grub 

 and root lice are common examples. Still other insects live 



