434 



with representatives present in nearly all land areas of the 

 earth. In Europe, North America and Australia the largest 

 nnnilx'i" of species have been described but some are known 

 from most all other countries. Much remains to be learned 

 about the psyllid fauna of the south Pacific lands, Asia, South 

 America and Africa, and until more is known especially of 

 the first our knowledge of the Hawaiian fauna and its origin 

 Avill be limited. 



The several hundred species of Psyllidae of the world have 

 been grouped into six subfamilies^ characterized ])y wing 

 venntional features or peculiarities of the skeleton of the head 

 or thorax. In Xorth America five of the six subfamilies are 

 represented, three very extensively and two less so. In Asia 

 five of the six have representatives known and perhaps of the 

 other also. In the Philippine Islands and Malay Archipelago 

 at least four and perhaps all of the six groups have representa- 

 tives. In other words, these insects have been well dissemi- 

 nated throughout the w^orld, especially Avhere land bridges have 

 permitted a wider migration. 



In the Hawaiian Archipelago, however, only one of the six 

 subfamilies is represented, so far as known at present, and 

 that by fifteen species falling into five genera, and thirteen of 

 the fifteen are so suggestively similar in certain fundamental 

 characteristics that one can scarcely avoid the conclusion that 

 they have sprung from one common ancestral form. The extent 

 of evolutional changes effected in this small fauna seems to 

 indicate a considerable lapse of time since the first introduction. 



The subfamily Triozinae, to which all the Hawaiian species 

 belong, is a specialized group set apart from the others by cer- 

 tain wing venational characters. The largest genus in the sub- 

 family is Trioza, to which about one hundred species have been 

 assigned throughout the world. Most of these species live free 

 on leaf surfaces, sucking out the juices without forming galls 



1 For details of classification the reader is referred to the author's 

 monograph of this family. Bulletin 85 of the U. S. National Mu- 

 seum, 1914. 



