170 AN INTRODUCTION TO ENTOMOLOGY. 



the hops by some members of the eleventh agamic generation a 

 generation of winged males. These fly to the plum-trees and mate 

 with the wingless sexual females, which are already there. Soon 

 after this the eggs are deposited on the smaller twigs and branches 

 of the plum, in and around the angles formed by the buds and twigs. 

 Each female lays from one to three eggs. 



If it should be proven that this species can winter only on plum, 

 the separation of plum and hop culture would be advisable. But 

 further observations are needed before we are warranted in advising 

 the destruction of plum-trees in the hop-growing sections. But we 

 can urge the careful destruction of all Aphids on plum-trees early in 

 the season. The most practicable way of doing this is by spraying 

 with a strong solution of soap or with kerosene emulsion. (See 

 Chapter XIV.) 



Family V. — Psyllidae* 



{Jumping Plant-lice^) 



The Jumping Plant-lice are comparatively small insects; our 

 more common species measure only 3 or 4 millimeters in 

 length ; and our largest species, the giant, comparatively speak- 

 ing, measures only 6 mm. and has a wing-expanse of 12 mm. 

 They resemble somewhat the winged Aphids in appearance ; but 

 they look more like miniature Cicades (Fig. 139). 

 They are, however, closely allied to the Aphids ; but 

 they differ from them in the firmer texture of the 

 body, in the stouter limbs, in having the hind legs 

 fitted for jumping, and in the 9- or 10-jointed an- 

 tennae. The antennae are peculiar also in being 

 armed at the tip with two bristles, or less commonly 

 FlG 'enfarged?' //a ' with one. " The rostrum is short, three-jointed, and 

 placed almost between the fore coxae, where it fits into 

 a grooved space. Both sexes are always winged in the adult ; the 

 wing-covers are ample, and, while often transparent, are much thicker 

 than the wings, and furnished with stout curving veins, which 

 enclose a few areoles at the tip." (Uhler.) 



The Psyllidae subsist entirely upon the juices of plants ; many 

 species form galls. But it is rare that any of them appear upon culti- 

 vated plants in sufficient numbers to attract attention, except in case 

 of the Pear-tree Psylla. 



* Psyllidae, Psylla : psylla (ipvXXa), a flea. 



