244 Agricultural Experiment Station, Ithaca, N. Y. 



have a case of true dimorphism. The summer form is the typical 

 Psylla pyricola, and may be desijjnated when necessary to refer to 

 this form alone as PsvUa pyricola pyricola; while the hibernating 

 form should be known as Psylla pyricola simulana 



Honey-devN^ and excrementb. — 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 throuj^h the punctures 

 made by the insects. As the honey-dew occurs in such immense 

 quantities it does seem almost, impossible that it is wholly the 

 secretion of the little creatures. All of this fluid does, however, 

 first pass throujrh 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 feeding apparatus, both in the nymph (Tig. 2 b, p. 223) and 

 the adult stage consists of a short, pointed bealc which appar- 

 ently rises from between the front legs. The sucking organs 

 are three long thread-like setae which move along grooves in the 

 beak; in many cases, when the nymphs are quickly killed, the 

 setae are found extruded as shown in Fig. 2, page 233. In 

 sucking, the point of the beak i& placed against the tissue and 

 the setae are forced into the sap cells. The sapf is then drawn 

 up through the beak into the body. In the case of the nymphs 

 most of the food is elaborated into honey-dew; some is assimi- 

 lated, and the waste matter voided as excrement. The adults, 

 however, seem to secrete no honey-dew, all the food being assimi- 

 lated. Consequently, the adultfe void considerable quantities of 

 excrement, much more than do the nymphs. 



The honey-dew and excrement are very different substanci^, 

 but the fact does not seem to have been before observed. The 

 honey-dew is a clear water-like liquid and forms into globules 

 when secreted. The excrement, however, is a whitish semi-solid 

 substance which is voided in long cylindrical strings, or minute 

 whitish balls which roll from the anus like quicksilver globules. 



