433 



lower part of the head next to the thorax and passes back 

 pressed against the ventral snrface of the thorax between the 

 front pair of legs and then bends downward. In this way a 

 greater leverage by more of the body is bronght to bear npon 

 the beak in forcing it into plant tissues. 



The immature, or nymphal, stages of these insects are 

 passed npon the same plants with the adults, and in the same 

 active, sap-sucking manner detrimental to the plant. In many 

 species the reaction of the insects' activities on the leaves or 

 stems of the plant and the poison wastes secreted by the insects 

 cause the growth of tumors or excrescences of characteristic 

 forms, known as galls. The galls are usually characteristic 

 of certain species and may often be used as an index of the 

 species even though the insects themselves may not be discov- 

 ered. 



The feeding habits of jumping plant lice render them harm- 

 ful to plant life, but fortunately these tiny insects do not at- 

 tack many of our cultivated or garden plants and therefore 

 they are considered of relatively small economic importance 

 in agriculture. Moreover, they are far less prolific than are 

 the true plant lice and scale bugs, and for this reason also are 

 viewed with much less concern by economic entomologists. 



There are a few species of the family which cause consid- 

 erable damage in the orchard, field or garden. The pear 

 psylla (several species, one in each of several countries) causes 

 extensive damage to pear and allied orchard trees and receives 

 much attention and expensive treatment. The tomato psyllid 

 (Paratrioza cod'erelU) is responsible for severe injury to 

 tomatoes and peppers and other plants in southwestern United 

 States, The laurel psyllid {Trioza alacris) seriously disfigures 

 bay trees in Northern Europe and now in the United States, 

 causing the leaves to become much rolled, curled up and gen- 

 erally distorted. Other species attack alder trees in America 

 and Europe, while another is a pest on citrus trees in the 

 ^lalay Archipelago and India. 



The family is a relatively small and homogeneous groii]i. 



