358 Fruit-growing in Arid Regions 



easily observed. But it is plain that they do not devour 

 leaves or bite holes into fruit. Some of them, in fact, 

 remain stationary during the most of their lives. Close 

 observation will show that in place of jaws this class 

 of insects is provided with sucking mouth-parts. They 

 must, therefore, pierce the bark, or epidermis, and suck 

 the juices from the parts on which they feed. It is evi- 

 dent that it is impossible to poison such insects. In 

 order to be a successful orchardist, one must make a care- 

 ful study of orchard pests, as many of them require 

 special treatment. 



When it is possible to prevent the spread of plant dis- 

 eases by spraying, bordeaux mixture has been almost 

 universally used. Biting insects may be killed by poison- 

 ing their food; arsenate of lead has come to be the stand- 

 ard poison for this purpose. The sucking insects must be 

 killed by some agent that suffocates or corrodes. Deadly 

 gases are sometimes employed, but more commonly some 

 mixture or solution is used that may be applied in the 

 form of a spray, such as the lime-sulfur mixture or the 

 tobacco decoctions. While good spraying is always neces- 

 sary, it is specially important with sucking insects, as 

 each individual must be hit by the spray. 



The codlin-moth is sprayed for before the eggs are laid. 

 The larvae, or worms, do not hatch till several weeks later, 

 but if the spraying is well done, the first mouthful results 

 in the death of the insect. But as the sucking insects 

 cannot be poisoned, it is no use to spray for them until 

 they make their appearance, unless, indeed, the eggs are 

 to be killed by a winter spray. 



