84 PROTECTIOX OF PLANTS, 1917-18 



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 gene- 

 rations 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 15th; 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 wing- 

 less sexual forms. Each female lays one large 3'ellow 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, 1-20 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 north- 

 ward. 



Parasites. — Aphelinns maU, 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 or suspected nursery stock in same 

 solution or fumigate with HCN ; add tobacco dust to the soil. 



Black Peach Aphis (Aphis persicae-niger Er. Sm.) — Black; lives on rose 

 twigs and leaves. No migration. Of no economic importance in Ontario. 



Mealy Plum Louse {Hyalopterus arundinis Fab.) — Has long narrow light 

 green body with three longitudinal stripes; covered wtth a mealy powder; honey- 

 tubes short and thick; winged females migrate in June to grasses and cat- tail and 

 return in autumn. 



Variable Currant Aphis (Aphis varians Patch). — Infests currants, gooseberries 

 and flowering currants, causing curling of the leaves. The winged summer 

 forms migrate to some unknown host, and return in the fall. The eggs are 

 deposited on the twigs. The stem-mother is purplish-green with white honey 

 tubes. The winged form has a black head and body, with a dark green abdomen 

 marked with black, while the wingless form is dark green, tan or dark brown. 



