146 ECONOMIC ENTOMOLOGY 



stock is liable to infestation and severe injury. The injury to the 

 branches is not so serious, but in cases of severe infestation it causes 

 stunted growth and yellowing of the leaves. Colonies often collect 

 at the axils of leaves, on water-sprouts, and at abrasions and wounds. 



The common form seen on roots and limbs is wingless, }-{o inch long, 

 reddish-brown, and covered with a woolly waxy excretion (Fig. 97). 



The life-history of the trunk forms is as follows: 



Some winter near the base of the apple tree as immature nymphs; 

 but those in the elm as eggs in crevices of the bark. The hibernating 

 nymphs on the apple migrate to the branches in early spring, and a 

 succession of parthenogenetic generations of apterous viviparous 

 females appears throughout the season. From the eggs on the elm 

 hatch out apterous viviparous stem-mothers in early spring about May 

 15 th, the second generation is also apterous viviparous, but the third is 

 winged and migrates to the apple, hawthorn and mountain ash where 

 three generations are developed, two being apterous, and the third 

 part apterous and part winged. The winged form migrates back 

 to the elm, and produces the wingless sexual forms. Each female 

 lays one large yellow egg which winters on the tree. The wingless 

 forms remaining on the apple give rise to another generation which 

 winters over as immature nymphs. 



The injury to the elm leaves is characteristic — the formation of 

 terminal leaf clusters or rosettes. S. americana produces leaf-curl. 



The winged forms are nearly black, the abdomen being rusty brown, 

 the wings are clear and the antennae have annulations and are 6-jointed. 

 The sexual forms are wingless, beakless, smaller than the agamic 

 forms; the female 3^^o inch long, reddish-yellow, is larger than the 

 olive-yellow male; the antennae are 5-jointed, and without annulations 

 as in other apterous forms. The root colonies ordinarily remain 

 underground throughout the year, and do less injury northward. 



Parasites. — Aphelinus mali, a chalcid; Pipiza radicum, a syrphid; 

 lady-bird beetles. 



Control. — Spray thoroughly the aerial forms with kerosene emulsion, 

 soap solution or tobacco decoction; dip roots of suspected nursery 

 stock in same solution or fumigate with HCN; add tobacco dust 

 to the soil. 



Black Peach Aphis {Aphis persicce-niger Er. Sm.). — Black; lives 



