TWO LEAFHOPPERS INJURIOTTS TO APPLE NURSERY STOCK. 5 



As a result of the continued checking of the growth, due to the in- 

 festation of the apple leafhopper, nursery apple trees often require 

 an additional ycai''s growth before they become of marketable size. 



EXTENT OF INJURY AND INFLUENCING FACTORS. 



The extent of injury varies according to the age of the nursery 

 stock and according to the differences in the character of growth of 

 apple varieties. 



Seedlings and the initial growth of buds and grafts are very seriously 

 injured. Nursery stock at this stage is in its most critical period of 

 growth and is injured very easily. Furthermore, any injiuy at this 

 stage is not readily outgrown. 



lifter the first year's growth the more vigorous varieties become 

 partially immune to serious injury and succeed in maintaining a 

 satisfactory growth, while slow-growing and tender-leaved varieties 

 are at all times badly injm-ed by the attack of this insect. This is 

 easily understood since, even under normal conditions, the latter 

 ' make but a very ordinary growth and are entirely unable to with- 

 stand a serious check. Among the varieties most severely injured 

 in Pennsylvania nurseries Red Astrachan, a particularly slow grower 

 during the first two seasons, ranks first, followed by Smith's Cider, 

 Starr, Early Harvest, Summer Rambo, Delaware Winter, Wagoner, 

 Golden Russet, Early Ripe, Wealthy, and Alexander. 



description of stages. 



Egg. 



PI. m:, I. 



Tlie egg is elongate, subcylindrical in form, very delicate, slightly curved from end 

 to end, somewhat roxmded at both ends but more so at the anterior one. "When first 

 deposited it is rather transparent but in a few days it changes to a pale yellow color, 

 while a small white cap forms at the anterior end through which the red eyes of the 

 immature nymph are perceptible. 



Average length of 15 eggs 0.82 mm., width 0.25 mm. 



Nymph. 



PI. Ill, A-F. 



First instar. — Color pale white, changing to a light yellowish green after feeding. 

 Eyes dull red. Small pale spines on the dorsal side of the head, thorax, and abdomen ; 

 the latter with four spines to each segment arranged in two longitudinal rows along 

 each side, one spine situated dorso,laterally, the other ventro-laterally. Posterior 

 margin of metathorax blunt. First two segments of antennae pale, the remainder 

 dusky. Average length of 16 specimens 1 mm. 



Second instar. — General color light yellowish green. Eyes lose some of their 

 red color. Posterior border of metathorax sharp in outline. First two segments of 

 antennae light yellow, remainder dusky. Average length of 16 specimens 1.30 mm. 



Third instar. — General color pale yellowish green. Eyes almost pearl white. Body 

 more robust than in first two stages. Wing pads appear as lateral buds extending 



