SPRUCE- AND LARCH-APHIS. 227 



for at least 2 or 3 years to have the slightest chance of success. Besides 

 the direct damage done, an entrance is opened for spores of the canker- 

 fungus on Larch and of Septoria parasitica on Spruce. 



The form known as the * Spruce-gall aphis, Chermes abietis, is only 

 about T V in. long, yellowish-green or light-brown, and (when present) 

 white wings and whitish bloom. About 25 eggs laid on the edges of bud- 

 scales hatch out, suck the sap, and form the small rough cone-like gall, 

 green at first, then brown and dry when the wingless brood emerges in 

 July or August. The intermediate form, the * Larch aphis, Chermes 

 laricis, mostly attacks young trees in nurseries and plantations 10 to 20 

 years old, and from May onwards is noticeable from its fluffy white coat- 

 ing. Under ^ in. long, purplish- or blackish-brown, and covered with 

 white fluff, it inserts a long sucker into Larch-leaves and feeds on their sap, 

 then lays about 45 eggs on the twigs, which on hatching out scatter and 

 live on the leaf -sap, soon get covered with white woolly down, fly and lay 

 eggs from July to August. Extermination of Ch. abietis -laricis can only 

 be successful by simultaneous collection of the young green galls on 

 Spruce and spraying of infested Larch (and other intermediate hosts, such 

 as Pine or Silver Fir) with insecticide for at least 3 years continuously. 

 The best spray for Larch aphis is to dissolve 3 Ibs. soft soap in J gallon 

 boiling water, stirring well till soap all melted, then add 1 pint paraffin 

 to the still boiling mixture, and churn the whole till well mixed ; to this 

 add 5 gallons of soft water, and stir thoroughly when spraying. 



The Bed Spruce aphis, Ch. coccineus, produces similar but smaller 

 false cones on Common and Menzies Spruce, at tip of twigs. The Elm- 

 blister aphis, Schizoneura ulmi, produces large, heavy, sticky galls on 

 the tips of Elm-shoots and leaves, and the Elm-gall aphis, Tetraneura 

 ulmi, small club-like galls on the upper side of Elm leaves. 



Among the Scale-insects (Coccidce), * the Felted Beech-scale, Crypto- 

 coccus fagi, a wingless, legless, lemon-yellow louse only 53- in. long (of 

 which the form is not yet known), which punctures the bark, sucks 

 the sap, permits the entrance of the spores of the canker-fungus, Nectria 

 ditissima, and often kills the tree, unless exterminated by scrubbing with 

 caustic alkali washes, or by spraying with paraffin emulsion (as for Larch 

 aphis). The Felted Ash-scale, Apterococcus fraxini, on young Ash-trees 

 after a heavy thinning on light gravelly soil, and the Felted Willow- scale, 

 Chionaspis salicis, on Willow and Ash, are also similarly destructive, 

 unless exterminated. 



[GERMINATION TABLES. 



