HOMOPTERA 



411 



The jumping plant-lice are very active little creatures, jumping 

 and taking flight when 

 disturbed; but their 

 flight is not a prolonged 

 one. They subsist en- 

 tirely upon the juices of 

 plants; some species 

 form galls ; but it is rare 

 that any of the species 

 appear on cultivated 

 plants in sufficient nimi- 

 bers to attract attention, 

 except in case of the pear- 

 tree Psylla. 



The family Chermi- 

 dae is of moderate size; 

 in our latest list one- 

 hundred thirty-seven 

 species representing 

 twenty-four genera, are 

 enumerated from our 

 fauna. The two fol- 

 lowing species will serve 

 to illustrate variations in 

 habits of these insects. 



Pachypsylla celtidis- 

 mamma. — This is a gall- 

 making species which in- 

 fests the leaves of hack- 

 berry {Celtis occidentdlis) 



with galls, and a single gall and a nymph enlarged 

 (Fig. 485) has a wing expanse of about 6 mm. 



The pear-tree psyllia, Psyllia pyricola.- — -This is our most impor- 



Fig. 484. — Gall of Pachypsylla celtidis-mamma: 

 c, leaf with galls, from under-side; Z>, section of 

 gall enlarged and insect in cavity; c, nymph, 

 enlarged. (From Riley.) 



Figure 484 represents an infested leaf 

 The adult insect 



Pig. 485. — Pachypsylla celtidis-mamma. (From 

 Packard.) 



Fig. 486.— Psyllia 

 pyricola. 



tant species from an economic standpoint, being a serious enemy of 

 the pear. It is a small species (Fig. 486) ; the stimmer generations 



