26 



INSECT PESTS OF FARM, GARDEN AND ORCHARD 



most biting insects which chew the leaves. Sucking insects must 

 therefore be killed by other means. 



How Insects Breathe 



Along the side of a caterpillar or larva, on one thoracic seg- 

 ment and on each abdominal seg- 

 ment except the last, is a small oval 

 spot, in the centre of which is a slit 

 closed by two membranous lips. 

 These apertures are called spiracles 

 or stigmata (Fig. 21 sp.), and are 

 the openings of the respiratory sys- 

 tem. Similar openings are to be 

 found in all insects, though not so 

 easily seen in the adults. Connect- 

 ing these spiracles is a pair of tubes 

 on each side of the body, through- 

 out its length, from which branch off 

 smaller tubes to all of its organs 

 and tissues. Fresh air is inhaled 

 to all parts of the body through 

 these tubes (Fig. 21, tr). 



The blood of insects does not 

 circulate through any system of tubes 

 as it does in the higher animals. 

 Along the middle of the back, 

 above the alimentary canal, is a 

 long tube popularly called the heart 

 (Fig. 23, d. v.). This heart is com- 

 posed of a number of chambers, 

 each of which is furnished with 



FIG. 19.-Cicada, showing mouth- side valves for admitting blood from 

 parts of a bug, a sucking insect; the body-cavity. The blood coming 

 lt S rum (T GO ^int ^to the heart from the body-cavity 

 tween forelegs; b, head removed: is propelled forward toward the 



IbTiter^^iiU^ te; head > where it a S ain flows into the 

 lab., labium. body-cavity. Thus various currents 



of blood are maintained throughout the body, but other than 

 the heart there is no system of blood-vessels, the blood merely 

 filling the body-cavity around and through the various organs and 



