February, ’18] 
LATHROP: APPLE LEAF-HOPPERS 
147 
but the increase in the numbers of adults was more rapid than the in¬ 
crease in the numbers of the nymphs, so that during early August, the 
adult was the greatly predominating form. During the first half of 
August nymphs of the second generation gained the ascendency, and 
it was during this period that the earliest adults of the second genera¬ 
tion appeared. By late September adults were very abundant, and 
most of the nymphs were of the later instars. However, all stages of 
the insect continued to be present until frosts killed the remaining 
nymphs. It seems quite probable that these nymphs which emerged 
so late in the season represented a third generation from eggs deposited 
by the more precocious adults of the second generation. It is doubtful 
if any of these reached maturity and were able to pass the winter. No 
evidence of oviposition in the bark of the infested trees could be found, 
Empoasca unicolor. This species spends the winter in the egg stage. 
The hatching occurred somewhat later than that of Empoa rosce and 
nymphs appeared during the last week in May. Development was 
slow as compared with the other species under observation, and adults 
did not appear until the first week in July. By 
the middle of the month all of the nymphs had 
matured. The insect is single brooded, and no 
eggs were observed until late fall, when the 
overwintering eggs are deposited in the bark of 
the apple. 
Habits and Nature of Injury 
When living on the apple, Empoasca mali is 
found feeding almost exclusively on the tender 
terminal growth, and it is for this reason, per¬ 
haps, that the species shows a marked preference 
for young, growing trees. Empoa rosce and Em¬ 
poasca unicolor both confine themselves very 
largely to the older leaves, although they occur 
on both old and young trees. However it was 
noticed that Empoa rosce was more prevalent on 
the older trees, while Empoasca unicolor was most 
abundant on younger trees. 
The attack of Empoasca mali causes a severe and 
characteristic curling of the foliage and resultant 
injury to the tree. Both of the other species destroy the chlorophyl 
of the leaves, with a consequent reduction of their value to the tree. 
Fire Blight Transmission 
A series of experiments was undertaken to determine the possibility 
Fig. 7, Typical in 
jury to apple by^Fra 
poasca mali. 
