HYMENOPTERA 345 



Suborder CLISTOGASTRA * 

 The Parasitic Hymenoptera, and the Ants, Wasps, Bees, and Allies 



The most striking characteristic of this suborder is the fact that what 

 appears to be the first abdominal segment, but which is really the second, 

 is greatly constricted forming a slender petiole or waist between the 

 larger portion of the abdomen and the alitrunk or wing-bearing region of 

 the body (Fig. 582). 



In this suborder the intermediate region of the body 

 is not merely the thorax but includes also the first ab- 

 dominal segment, only the tergum of which is preserved 

 in the adult. This is known as the median segment, 

 or the propodeum and can be identified by its spiracles, the third pair of 

 this region of the body. It should be remembered that the thorax bears 

 only two pairs of spiracles. From the above it follows that what appears 

 to be the first abdominal segment in the Clistogastra, and which is usually 

 so-called, is really the second. 



In some the ovipositor is a boring instrument by means of which 

 deep holes are made into trees and eggs placed in these holes ; in others 

 it is used for thrusting the eggs into the bodies of other insects; and in 

 still others it is modified so as to form a sting with which poison glands 

 are connected. 



THE PARASITIC HYMENOPTERA 



When the discouraged farmer sees his crops harvested before due time 

 by hordes of hungry insects, he is apt to long for a miracle to remove the 

 plague from his fields. Oftener than he dreams the miracle takes place, 

 and millions of insect pests never live to lay their eggs for another brood. 

 Such miracles are frequently wrought by members of a large group of in- 

 sects, which is commonly known as the parasitic Hymenoptera. 



Although some of these insects are external parasites, most of them 

 live within the bodies of their hosts, within which they pass their entire 

 larval existence. Their presence in this strange situation is due to the 

 fact that the parent lays her eggs within or upon the body of the victim. 

 When the egg is laid upon the body of the victim the larva as soon as it 

 hatches bores its way into the body. So in either case the young parasite 

 is in the midst of suitable food. It is probable that the parasite feeds at 

 first only on the blood of its host; hence the parasitized insect is not 

 destroyed at once, but lives on with the parasite within it, which grad- 

 ually attains its growth. Finally, the parasitized insect perishes; and from 

 the larva that has been nourished in its body there is developed a winged 

 creature, which in turn lays its eggs in other victims. Frequently a para- 

 sitic insect lays several eggs within a single victim, so that a number of 

 parasites may be developed within the body of a single insect. Each 

 species of these parasites infests only certain insects, each insect having, 

 to a great extent, its peculiar parasites. 



The parasitic Hymenoptera does not constitute a natural division 

 of the order but includes representatives of many families. 



* Clistogastra: clisto (-xXtiaTos) , closed; gastros (yaa-rpos), the belly. 



