The Pear Tree Pstlla. 231 



fauna of Europe comprises more than 150 described species and 

 has been thoroughly studied. Dr. Franz Low, of Vienna, added 

 much to our knowledge of the classification of this group, iindi 

 he has described the life histoiy and habits of several species.* 



Dr. E. Witlaczil, of Vienna, has written exhaustively on the 

 anatomy of the family. § 



In the United States but little attention has been paid to the 

 Psyllidae, and less than twenty species have thus far been recog- 

 nized. 



Three species of PsyUa infest the pear-tree in Europe — pyri- 

 suga, pyricola and pyri; pyrisuga does the most damage, and 

 pyri is comparatively rare. We have, as yet, no native species 

 of Psylla feeding on the pear tree. Our pest, Pyslla pyricola, 

 although it was observed in this country in 1833, received its 

 name in Europe fifteen years later, or about the time Dr. Harris' 

 attention was called to it here. Previous to 1848, European 

 writers had referred to the species as Psylla pyri, not distin- 

 guishing it from that species; and nearly all of our entomologists, 

 have written of it under this name. Psylla pyricola sometimes 

 attacks the apple-tree in Europe, but it seems to confine its 

 attacks to the pear in this country. 



Indications of its Presence. 



Among the first indications that pear growers, who suffered 

 from this pest in 1891, had of its presence was the noticeably les- 

 sened vitality of their trees early in the season. Old trees, 

 especially, put forth but little new growth. Where new growth 

 started, in many cases, the shoots began to droop and wither in 

 May as if from a loss of sap. A little later, whole trees put on a 

 sickly appearance; the leaves turned yellow and the fruit grew 

 but little. By midsummer nearly all the leaves and half -formed 

 fruit fell from many trees; this fact suggested the design on the 

 title page of this bulletin. 



Another peculiar phase of the attack was the immense quan? 

 titles of a sweet water -like fluid called honey-dew which covered 



*In Verb, der K. K. Zool. — Bot. Ges. in Wien, 186^1886. 

 §Zeit. fur Wissensch Zool. XLH, 569 (1885). 



