PART IV. 



INSECTS AND PLANT DISEASES AND THEIR 

 CONTROL 



EXERCISE 63 



THE STRUCTURE OF AN INSECT 



Fig. 92. Frontal view 

 of head 



Statement. Some insects are beneficial, others injurious, yet others are both helpful and harmful, 

 and yet others are apparently of no direct importance. Man has been able to meet and utilize these 

 relations largely by first learning how they carry on their life 

 activities, such as feeding, breathing, and reproduction. 

 Since all of these activities are directly related to certain 

 structural features of the insect, a knowledge of its structure 

 is essential. 



Object. To study the structure of the common grass- 

 hopper. 



Materials. A common grasshopper ; hand lens ; drawing 

 pencils and eraser. 



Directions. Study the body covering and note that it is 

 rigid and is composed of a series of ringlike units called segments. These seg- 

 ments differ in various parts of the body, but the similar ones are grouped 

 together to form the three body regions, head, thorax, 

 and abdomen. 



1. The head appears to comprise but one segment, 

 but in reality six are fused together to form it. Two 

 slender antennae extend from the upper part of the head. Two compound 

 eyes and three simple eyes (ocelli) are also easily observed. The mouth parts 

 are of the biting type and composed of four distinct superimposed sets, 

 namely, upper lip, or labrum ; a pair of jaws, or mandibles ; a lower pair of 

 more complex jaws or maxilla? ; and the lower lip or labium. 

 The maxillae and the labium bear each a pair of jointed ap- 

 pendages known as palpi. 



2. The thorax, or middle-body region, is composed of three 

 segments, each of which bears a pair of legs. The first segment 

 (prothorax) is covered on the top and the two sides by a heavy, 

 thickened, saddle-shaped shield. Each of the next two segments (mesothorax 

 and metathorax) bears a pair of wings. A diagonal line (suture) extends 

 across the side of each of these last two segments, making them appear to be 

 four segments instead of two. Just above the base of the middle leg and in the 



Fig. 88. 



Dorsal view 

 cricket 



of 



Fig. 89. Lateral 

 view of head 



Fig. 90. Lateral view 

 of thorax 



Fig. 91. Lateral view of abdomen 

 [1261 



Fig. 93. Mouth parts 



0, labrum ; b, mandibles ; c, n 

 ilia; ; d, labium 



