HYMENOPTERA 917 



GG. Mesopleura divided by a transverse suture into an upper and 

 lower plate. Coxae very large and long; the legs long and usually 



distinctly spinose. p. 950 Pompilid^ 



DD. First abdominal segment forming a "scale" or "node" between the 

 propodeum and the gaster. Thorax with its sutures distinct, but the 

 mesothorax usually much reduced in size. p. 954 Formicid^ 



SuPERFAMiLY ICHNEUMONOIDEA 

 The Larger Parasitic Hymenoptera 



Often after a great outbreak of insects people are astonished that 

 the hordes of pests have disappeared so quickly and completely. 

 Few of them realize that the subjugation of the pests was probably 

 due either to the weather or to the activities of parasitic insects. In 

 this superfamily are included some of the parasites most often re- 

 sponsible for the control of insect outbreaks. They perform also the 

 less noticeable but more important role of keeping most species of 

 herbivorous insects below the level of economic importance. 



Entomologists have made many attempts to supplement the 

 activities of native parasites with introduced species. Usually this 

 has been a matter of going to the native home of an introduced pest 

 for the purpose of bringing in the insects found to attack it there. 

 Some introduced parasites have found conditions in their new home 

 favorable for rapid and continued reproduction and have effected 

 spectacular control. Pests of major importance have been reduced 

 to insignificant numbers in a few years. Most attempts to introduce 

 beneficial insects have met with failure or with very moderate success 

 due to the inability of the parasite to establish itself or to build up 

 sufficient numbers. A single success in this field of work, however, 

 more than compensates for many failures. 



In the parasitic superfamily Ichneumonoidea are included the 

 Stephanida?, Braconidas, Ichneumonid^, Trigonalidse, Aulacid-e, and 

 Gasteruptiid^. In these families are most of the larger species of 

 parasitic Hymenoptera. They have rather complete venation in the 

 fore wing, no anal lobe in the hind wing, and an indefinitely large 

 number of antennal segments, usually seventeen to sixty or more. 

 The multi-segmented antenna is the only distinctive character of the 

 superfamily and this is subject to the exception that the Aulacidse 

 and Gasteruptiidse have only fourteen antennal segments. This 

 obvious lack of cohesion makes one doubt the naturalness of the group. 



Correlated with its parasitic habits the larva of ichneumonoids 

 is degenerate, legless, and maggot-like. Except for the mandibles 

 the head appendages are more or less vestigial. The body has thirteen 

 segments and in the mature larva nine pairs of spiracles. Ichneu- 

 monoid larvse differ from those of parasitic Diptera in lacking the 

 mouth hooks and pharyngeal skeleton so characteristic of the latter. 

 They differ from chalcidoid larvae in having the labium and maxilla 

 present or represented by sensory areas. These organs are not de- 

 tectable in the chalcidoids. 



The ichneumonoids are all parasites upon other arthropods. 



