INSECTS AND INSECTICIDES 



363 



The wings are modified in various ways; in the butterflies 

 and moths they are usually eovered with scales ; in the beetles 

 the front wrings are hard and horny and are known as wing- 

 covers under which the hind wings 

 are folded when in repose. In many 

 true bugs the front wings are of a 

 leathery texture except the tip, which 

 is membranous. 



In the female the abdomen is often 

 provided with a sharp ovipositor by 

 means of which she is able to insert 

 her eggs into the tissue of plants. 



Hoiv insects feed. 



The mouth-parts of insects are 

 adapted for feeding in various ways 

 and on all kinds of plant tissue. In 

 order to make intelligent efi'orts to 

 control insects, it is necessary to 

 know exactly in what way they take 

 their food. For purposes of control, 

 insects may be roughly divided into 

 three classes as follows : 



1. Chewing insects: In this group 

 the mouth is provided with a pair 

 of hard horny jaws or mandibles 

 (Fig. 229) wuth which the insect is 

 able to bite off portions of plant 

 tissue, which are then swallowed. 

 Beetles and caterpillars belong to 

 this class. It is usually possible to 

 kill such insects by poisoning their 

 food. Arsenic in some form is 

 generally employed for this purpose. 



Tarsus 



Fig. 228. 



Leg of a blister- 

 beetle. 



