262 STATE HORTICULTURAL SOCIETY. 



clavus. The male genitalia differ slightly in size in the two forms. Fig- 

 ure 3 represents an adult of the summer form; and the wings shown in 

 figure 8, are also from a summer adult. 



The hibernating adults were studied at the insectary in connection with 

 the descriptions of Psylla simulcms and Dr. Low's remarksj upon the dif- 

 ference between the pear psyllids. This study left but little doubt that 

 Psylla simulans was described from specimens of the winter form of 

 Psylla pyricola. 



This difference between the summer and the winter adults is common 

 among the Psyllidce, and has before led to their being described as differ- 

 ent species. It seem not to have been suspected that these insects were 

 truly dimorphic or appeared in two distinct forms during the year. The 

 general impression seems to have been that the adults appearing in the 

 fall were at iirst the same as the summer form; and that as winter 

 approached, these adults gradually assumed the characteristics of the 

 hibernating form. However, frequent observations upon Psylla pyricola 

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

 eggs laid about August 20, by typical summer adults, there hatched nymphs 

 which showed no variations from the typical summer nymphs and from 

 these nymphs there emerged about September 25, the distinct hibernating 

 form simulans. The hibernating forms feed until the leaves fall' and tlien 

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

 to copulate in the fall. Biit very few summer forms were seen after Sep- 

 tember 20. Thus in our pear-tree psylla we have a case of true dimorphism. 

 The summer form is the typical Psylla pyricola, and may be designated 

 when necessary to refer to this form alone as Psylla pyricola pyricola; 

 while the hibernating form should be known as Psylla, pyricola simulans. 



Honey -dew and excrement. — Many have supposed that the honey-dew, 

 so conspicuous a feature in severe attacks of this pest, is the sap of the 

 tree which exudes through the punctures made by the insects. As the 

 honey-dew occurs in such immense quantities it does seem almost impos- 

 sible that it is wholly the secretion of the little creatures. All of this fluid 

 does, however, first pass through the body of the insect. The amount which 

 a single individual will secrete during its lifetime is small, but when many 

 thousands of the insects occur on a tree, the aggregate becomes large. A 

 single nymph isolated in a cage, secreted at least four drops (i. e. four 

 minims) of the fluid before it became an adult. Thus fifteen nymphs 

 would secrete one drachm. 



The food of the insect consists entirely of the sap of the tree. The feed- 

 ing apparatus, both in the nymph (Fig. 2 6) and the adult stage con- 

 sists of a short pointed beak which apparently rises from between the 

 front legs. The sucking organs are three long thread-like setoe which move 

 along groves in the beak ; in many cases, when the nymphs are quickly 

 killed, the setse are found extruded as shown in Fig. 2. In sucking, 

 the point of the beak is placed against the tissue and the eetse are forced 

 into the sap cells. The sap is then drawn up through the beak into the 

 body. In the case of the nymphs most of the food is elaborated into 



tVerh. Zool. Bot. Gee. in Wien, 1886, p. 154. A translation of most of Dr. Lftw's article occnrs in Insect 

 Life, IV. 127. Dr. LOwgivesatabalarstatement of the differences between Pyrisuga &nd pyri and pyricnla, 

 and briefly points oat how. si'miti'irw differs from pvi and pyricola. A serione error occnrs in the translation 

 in connection with simidaiw. 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 clavns is larger with more black and in the hind basal eel) there is a brownish or blackish stripe 

 along the whole suture of the clavos. The forceps of the males are as in Psylla pyricola only a little 

 wider." 



