Pomona College Journal of Entomology 



707 



Pemphigus popiilimoiiUis Riley w;i.s first reported on the narrow-leaved 

 Cottonwood {I'opulus halsamifcra I,, var. augustifolia Torrey), but has since been 

 found feeding upon Populus trichocarpa T. & G. first by Gillette in Jr. Ec. Ent. 

 II, p. 356, lyoy, near Portland, Oregon. Davidson reports it from Populus fre- 

 monti in Jr. Ec. Ent. Ill, p. 374, 1911. 



LocalHi/ — The species as described was taken in large numbers along the 

 banks of the Santa Clara River near Santa Paula, Cal. 



Date of Collection — June 22, ipil. Serial number 40. 



Figure 226. Pemphigus populimonilis Riley 

 Underside of a leaf with the galls opened so as to show the aphids and the larvae 



of syrphid flies. 



I have been able to procure three descriptions of this insect; by Thomas (who 

 practically duplicates the original description given bj' Dr. Riley), Jackson and 

 Williams. From them I am led to believe that they are all practically the same 

 as that of the original description of Riley. Either the species was originally 

 and afterward very poorly described, or the species which I have described varies 

 a great deal from the individuals taken in the East. The following differences 

 are noted: 



Size — All of the above descriptions agree exactly regarding the size of the 

 species and their measurements are much less than those of the above specimens. 

 For instance, Thomas gives 6.4 mm. as the average wing expanse, while the 



