64 BULLETIN" 826, XJ. S. DEPARTMENT OF AGRICULTURE. 



large wax reservoir. The structure of the cornicles themselves in this 

 subfamily is essentially the same in all genera where they are present. 

 In a large number of genera, however, the wax reservoir is absent 

 and in some specialized tribes the cornicles are likewise absent. It is 

 interesting to note that in some genera, though absent in the stem 

 mother, they are present in the alate forms. 



The habit of gall formation is not found equally in all genera 

 and it would seem that those forms which have become associated 

 with ants have not developed this habit to the same extent as have 

 some of the other groups. However, it must be borne in mind that our 

 knowledge concerning the species associated with ants is very incom- 

 plete, and the writer is convinced that many of the Prociphilini will 

 be found during their summer generations in this relation. Many 

 of the forms cause true galls which are the result of outgrowths 

 of the plant and which completely enclose the insects. Sometimes 

 the stem mother lives in a gall by herself while in other cases the 

 following generations live with her. The original spring gall is usually 

 the result of the activities of the young stem mother. Certain species 

 do not produce true galls but form pseudogalls which are due to the 

 rolling or crumpling of the leaves on which the insects feed. Other 

 species, again, especially during their summer generations, feed on the 

 twigs or roots of plants and give rise to excrescences by their 

 feeding. It often happens that species which in their spring forms 

 are gall makers, attack plants in this way in their summer generations. 

 Others live on the roots of grasses during these generations and do- 

 not cause the excrescences produced by those species feeding on trees 

 and woody shrubs. 



The association with ants is highly developed by one tribe of this 

 subfamily, although all of the other tribes are to a degree tended by 

 these insects. The species of the Fordini live exclusively in the nests 

 of ants or are tended by them, and they are cared for very carefully 

 in return for the honeydew excreted. Ants also attend species which 

 have aerial feeding habits and they may be seen carrying the root 

 generations of species of Eriosoma from one place to another and 

 even distributing them about on the trees. Indeed the writer once 

 took advantage of the presence of ants to infest some apple seed- 

 lings. A vial of apterous insects was emptied at the base of each 

 tree and the ants soon could be seen running about carrying the 

 aphids to suitable positions on the trees. Sometimes, however, they 

 carried them away. 



