116 



ORDER HEMIPTERA 



cicadas, wings specialized, and they differ in the beak 

 being fused into the sternum. They are descended from a 

 generahzed insect like the cicada in character. The prin- 

 cipal line of specialization has been in the fusion of the beak 

 and sternum. It stands out at almost right angles to the 

 prothorax, between the front legs. 



All of the species are quite small. Some feed directly on 

 the surface of plants. Others present a distinctly specialized 

 food habit, producing galls on various trees, expecially 

 on the hackberrv. 



Fig. 72. — Pear-tree psylla: n, egK; b, larva, hut greatly enlarged. 

 (From Marlatt, Div. Eiit., U. S. Dept. Ag.) 



A common and destructive species in the Eastern States 

 is the pear psylla which causes serious loss in pear orchards. 



One of the most common is Pachi/psi/Ua ceJiidis-mamma. 

 The larvffi are found in cavities in the galls; the galls are 

 formed by the deposition of eggs on the surface of the leaves 

 and the stimulation of the leaf cells. The life-cycle must 

 lie adapted to the growth of the leaf on which it occurs. 

 In the gall, when dried up in the fall, are found either adults 

 or mature nymphs. The adults usually emerge and secrete 

 themselves in fallen leaves, etc. The adults appear in the 

 spring at about the time that the hackberry leaves are ex- 

 panding and (le])osit eggs on the surface of the leaves, and 



