THE CONTKOL OF PLANT LICE ON APPLE 



TREES* 



H. E. HODGKISS and B. B. FULTON. 



Plant lice are among the most harmful pests of the apple. During 

 recent years these insects have been very destructive in many orchards 

 in the leading apple-growing sections of New York. The species 

 of aphids which occur on this fruit are the green apple-aphis (Aphis 

 pond DeG.), the rosy apple- 

 aphis (Aphis sorbi Kalt.), the 

 European grain-aphis (Sipho- 

 coryne avenue Fab.), and the 

 woolly apple-aphis (Schizon- 

 eura lanigera Hausm.). The 

 most injurious forms are the 

 green apple-aphis and the rosy 

 apple-aphis. The woolly 

 apple-aphis is abundant only 

 in occasional years. 



NATURE OF INJURY. 



Injuries from plant lice 

 result chiefly from the extrac- 

 tion of plant juices by the 

 insects which feed upon 

 foliage (Plate XXI, fig. 

 1) and fruits. Young, 

 tender, growing twigs 

 and succulent sprouts 

 afford the most con- 

 genial conditions for 

 aphids and on those 

 they multiply very 

 rapidly. The lice choose 

 by preference the lower 

 and more dense portions 

 of the trees and are less 

 often found in the top- 

 most branches. The 

 work of the aphids dur- 

 ing May and June is 

 especially destructive 

 since it occurs during the period when next year's fruit buds are 

 forming and when the vigor of the trees is also required for the 

 development of the young apples of the current season's crop. If 

 favorable conditions exist for the rapid increase of the pests the 

 leaves become curled (Fig. 39) and the development of the young 



Fig. 39. — Leaves curling from aphis attacks. 



.Reprint of Circular No. 2:3, March 4, 1913. 



[365] 



