50 



INSECTS AND HUMAN WELFARE 



other very minute species are egg parasites, completing their 

 entire growth within the eggs of Uirger insects, within which 

 the female deposits her own minute eggs. The superfamily 

 Proctotrypoidea includes several families of minute species 

 which are egg parasites, developing in much the same way 

 within the eggs of other larger insects. To this group belong 



Fig. 24. A parasitic Tachina fly {Compsilura concinnata), 

 an enemy of the gipsy moth. 



also some other families with habits more like those of the 

 Ichneumonida?, which attack the later preparatory stages of 

 their hosts. 



Second in importance are a large series of Diptera belonging 

 to the family Tachinida^, parasitic during their larval devel- 

 opment within the bodies of other insects, mainly the cater- 

 pillars of various Lepidoptera, although they by no means 

 restrict their attacks to insects of this order. The Tachina 

 flies (Fig. 24) are in some ways less specialized in their habits 

 and as a rule do not have such definite host relations as the 

 parasitic Hymenoptera, most species attacking a larger and 

 more varied series of hosts. On the other hand, the methods 

 by which the larvae gain access to the host show highly de- 

 veloped adaptations. Some deposit large, oval white eggs 

 directly upon the caterpillars or other insects within which 

 they may develop, and the larvae on hatching bore through 

 the cuticle and gain entrance to the visceral cavity. Others 

 thrust maggots directly through the skin of their victims, 



