FAMILY APIIIDIDJE 



117 



during the rapid growing period of the leaf these galls are 

 developed and tiie larvje are growing within them. There 

 is a single generation during the year. This is the plan of 

 development for practically all of these psyllid galls. A 

 niuuher of different kinds occur on hackberry trees. They 

 are readily identified by the character of the galls produced 

 on the trees. iVIost species are located on the leaves, but 

 some species form a structure on the twig l)y a modification 



Fig. 73. — Pear-tree jisylla: nymph greatly enlarged. (From Marlatt, Div. 

 Ent., U. S. Dept. Ag.) 



of the bud. There is a distinct specialization in the matter 

 of food supply which characterizes a large part of the family 

 Psyllida^. Stimulation of the plant tissues is produced by 

 the action of the larvtie in puncturing the cells. 



Family Aphididse. — This family is specialized particu- 

 larly with reference to the mode of reproduction. It agrees 

 with other forms of the Sternorhynchi in having the beak 

 apparently fused with the prosternum, so that the beak 

 appears to arise from the sternimi. There is a reduction of 



