THE KANSAS UNIVERSITY 

 SCIENCE BULLETIN. 



Vol. V, No. 9] APRIL. 1910. [rrxV^NTs 



THE HACKBERRY PSYLLA, PACHYPSYLLA 

 CELTIDIS-MAMM^ RILEY. 



A STUDY IN COMPARATIVE MORPHOLOGY. 



BY H. B. STOUGH. 

 Plates XXVI to XXXV, and three figures. 

 (Contribution from Entomological Laboratory, No. 158.) 

 Submitted in partial fulfillment of the requirements for the degree of Master of Arts. 



OWING to their minute size and obscure life habits, the 

 members of the homopterous family Psyllidse have re- 

 ceived comparatively little attention in North America. In 

 the present paper an endeavor w^ill be made to add to our 

 knowledge of this family, using as a type Pachypsylla celtidis- 

 mammae Riley, the same being a study in comparative mor- 

 phology of mouth parts, thorax, and genitalia, and develop- 

 ment of v^ing venation and wing pattern. The specimens upon 

 which I have based my studies emerged from their galls upon 

 the hackberry trees during October of 1908, at Lawrence, Kan. 

 I wish to thank Prof. S. J. Hunter, upon whose suggestion the 

 problem was taken up, and under whose guidance and counsel 

 the work was carried on, for his interest in my investigations 

 and for his assistance rendered. 



In search for literature on the Psyllidse of North America, 

 and especially that dealing with Pachypsylla celtidis-mammx 

 and its genus, I was impressed with the fact that very little of 

 a definite and final treatment has ever been given to these in- 

 sects in this country. A few species have been described, a 

 few figured, and the life histories of a number worked out, 

 while keys for the species of only about one genus can be found. 



In Europe, on the contrary, the contributions to the knowl- 

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