The Peak Tkee Pstlla. 243 



invariably of a dark brown or black color; the front wings are 

 quite transparent with, more or less blackish shades in the cells 

 and a blackish shade in the baisal cell along the whole suture 

 of the clavus. The male genitalia differ slightly in size in the 

 two forms. Fig. 3 represents an adult of the summer form; and 

 the wings shown in Fig. 8 are also from a summer adult. 



The hibernating adults were studied at the inisiectary in con- 

 nection with the descriptions of Psylla simulans and Dr. Low's 

 remarks§ upon the difference between the Pear Psyllids. This 

 study left but little doubt that Psylla simulans was deisoribed from 

 specimens of the winter form of Psylla pyrioola. 



This difference between the summer and the winter adults is 

 common among the Psyllidae, and has before led to their being 

 described as different species. It seems not' to have been sus:- 

 pected that these insects were truly dimorphic or appeared in two' 

 distinct forms during the year. The general impresision seems 

 to have been tihat the adults appearing in the fall were at first the 

 same as the summer form; and that ais winter approached, these 

 adults gradually assumed the oharaoteristics of the hibernating 

 form. However, frequent observations upon Psylla pyricola lq the 

 field during August and September, 1892, have shown that from 

 eggs laid about August twentieth by typical summer adults, there 

 hatched nymphs which showed no variations fi-om the typical 

 summer nymphs and from these nymphs there emerged about Sep- 

 tember twenty-fifth the distinct hibernating form simulans. The 

 hibernating forms feed until the leaves fall and then seek their 

 hiding places in which to pass the winter. None have been seen 

 to copulate in. the fall. But very few summer forms were seen 

 after September twentieth. Thus in our Pear-tree Psylla we 



§ Verb . Zool . Bot Ges . in Wien, 188r., p . 154. A translation of most of Dr . Low's article occurs 

 in In>*ect Life, iv. U7 Dr. Low gives a tabular statement of the differences between Pyrisuga 

 pyri and pyricola, and briefly points out how simulans differs from yiyri and pyricola. A serious 

 error occurs in the translation in connection with simulans. The sentence preceding the last in 

 the translation should be divided into two, the period occurring after the phrase, "Along the 

 whole fold of the clavus." The remainder of the sentence is not only incorrectly translated, 

 but it should form a distinct sentence. Dr. Low says; "The tip of the clavus is larger with more 

 black and in the hind basal cell there is a brownish or blackish stripe along the whole suture of 

 the clavus. The forceps of the mule are as ia Psylla pyricola only a little wider." 



