THE CANADIAN ENTOMOLOGIST 375 



and C. pilulcB, respectively, as well as the conical and globose en- 

 largements of various species of Caryomyia upon hickory, must be 

 considered as extreme types or modifications of the blister gall. 



Stem galls. No part of the plant is exempt from infestation 

 by the small representatives of this large family, be it seed, flower, 

 leaf, stem or root. The stem gall is usually subcortical, and in 

 those produced by midges, development generally begins while 

 the tissues are still in a soft and plastic condition. They are usu- 

 ally polythalamous and are frequently irregular, more or less con- 

 fluent swellings in the bark. 



The medullary, stem or branch galls differ from the preceding 

 in that the larvae confine their operations to the interior of the 

 affected tissues, frequently restricting themselves to the pith and 

 producing rather characteristic deformities. . 



Root galls. There are only a few root galls known, probably 

 because of the great difficulty in finding them. There appears to 

 be no marked difference between these and the stem galls, aside 

 from the point of location. 



Recalling the fact that gall midge larvae are small, without 

 defensive armor or apparatus, with masticatory, or boring 

 organs poorly developed or absent, it is obvious that this gall- 

 making habit is one of the most important adaptations in the family. 

 The gall midges have been able to maintain themselves in hosts 

 and in many and varied forms by adaptations which have led to 

 their seeking sustenance and shelter in places comparatively free 

 from invasion by other insects. Not only have these small insects 

 learned to prey upon numerous plants, but some have found it 

 advantageous to wring sustenance from their associates. The 

 species of Lestodiplosis, in particular, may be reared from a great 

 variety of galls, and the larvae have even been observed preying 

 upon gall midge maggots, especially those of Miastor. Members 

 of this family have also learned the value of other insects as food, 

 and we now have records of a number of species preying upon scale 

 insects, various plant-lice and red spiders. 



Intimate relations exist between certain genera of gall-midges 

 and families and species of plants. It is perhaps sufficient to note 

 in this connection that the genus Cincticornia is practically con- 

 fined to Quercus, Caryomyia to Carya, Rhopalomyia largely to 



