1593.] Entomology. 293 
ENTOMOLOGY. 
The Pear-Tree Psylla.—During the last two or three seasons 
many pear orchards in Connecticut, New York and other States have 
suffered severely by the attacks of a small jumping plant louse of the 
family Psyllide. This insect is supposed to have been imported from 
Europe early in the present century, having been first noticed in Con- 
necticut. It now occurs throughout many of the Northeastern United 
States, and as far west as the Mississippi Valley. 
* Ina recent discussion `of this insect in Bulletin 44 of the Cornell 
University Experiment Station, Mr. Mark V. Slingerland records 
one of the most notable pieces of entomological work done since the 
establishment of the stations. After an introductory paragraph indi- 
cating the recent losses due to the pest the author considers its past 
history in America ; its place in zoological classification ; the indica- 
tions of its presence; the appearance of the immature and mature 
insect; its life history in detail, and the methods of preventing its 
ravages, all of which is followed by a series of technical descriptions 
and a full bibliography. One of the interesting points brought out is 
that the species is dimorphic, the summer form having been described 
as one species, and the winter form as another. Concerning this the 
author writes: 
“ This difference between the summer and the winter adults is common 
among the Psyllide, and has before led to their being described as 
different species. It seems 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 first the same as the summer form; and 
that as winter approached these adults gradually assumed the charac- 
teristics of the hibernating form. However, frequent observations 
upon Psylla pyricola in the field during August and September, 1892. 
have shown that from eggs lain about August 20th by typical summer 
adults, there hatched nymphs which showed no variations from the 
typical summer nymphs and from these nymphs there emerged about 
September 25th the distinct hibernating form simulans. The hiberna- 
ting 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 20th. 
1 Edited by Clarence M. Weed, Hanover, N. H. 
