February, ’18] 
LATHROP: APPLE LEAF-HOPPERS 
145 
or whitish color. The adult of Empoasca unicolor is larger and a trifle 
more robust than that of E. mali and the coloration of the two is quite 
distinct. However, the most reliable distinctive characteristics are 
the form of the female genitalia and the contour of the anterioF margin 
of the vertex. 
Seasonal Activities 
During the summer and fall of 1915 the district of western New York 
about Geneva experienced a heavy infestation of the apple leaf-hopper, 
Empoasca mali. The foliage of apples in nursery plantings and of 
young orchard trees was severely curled. Similar injury was com¬ 
monly observed on various ornamental nursery stock, and the writer’s 
attention was especially attracted by the injury to Norway maple and 
cut leaf birch. During this season infestation by Empoa rosce was 
also quite common, and their attacks were in evidence in all orchards 
observed. Empoasca unicolor , on the other hand, seemed to be com¬ 
paratively rare, and no cases of heavy infestation were observed. 
The season of 1916 was fully two weeks later than normal, and there 
was a consequent delay in the beginning of insect activities. During 
the spring and summer of this season conditions were somewhat re¬ 
versed with respect to leaf-hopper abundance. Empoasca mali, though 
still decidedly injurious, was much less iri evidence than during the 
preceding season, while Empoasca unicolor was exceedingly plentiful, 
proving to be a true pest and by far outnumbering E. mali. Empoa 
rosce was again prevalent, and, in spite of its natural enemies, did con¬ 
siderable injury. 
Life-History Studies 
Empoa rosce. This species spends the winter in the egg stage. By 
far the larger number of the winter eggs are deposited in the bark of the 
rose although a few occur on apple. 
On May 20, nymphs were found emerging from eggs on rose. The 
young nymphs immediately migrated to the underside of the leaves and 
began feeding. The hatching of nearly all of the eggs occurred almost 
simultaneously, and within a few days all of the nymphs had appar¬ 
ently emerged. The nymphs were common on roses, and many cases 
of very heavy infestation were observed. The apple, on the contrary, 
was almost entirely free of infestation, and only occasional nymphs of 
this generation could be found on this plant. 
The first adults of the season appeared during the second week in 
June, and from that time on, the number of adults increased, until, by 
the latter part of the month, practically all the nymphs had trans¬ 
formed. The adults migrated to apple, and after this, the rose was 
almost deserted. After the middle of July the adults began to decrease 
li 
