148 



Insect Pests. 



Thus in two ways we have the Woolly Aphis carrying on its 

 existence during the winter above ground : (1) as living viviparous 

 females ; (2) in the egg stage near the base of the tree. Besides 



KIG. 122.— ROUT FORM OP WOOLLY APHIS. 



living on the trunk and other parts above ground, Scliizoncura 

 lanifjera lives (3) on the roots and around the stem below ground. 

 The forms found beneath the soil are just the same as those living 

 above it. There they breed in the same way, produce galled growths 

 on the roots, swollen and cracked areas on the stem, and suck the 

 sap going to the plant. 



No ova has as yet been detected below 



^^^^ the soil. The actual root form, that is, the 



^^^^^^ race that galls the roots, is augmented during 



^^^^^^^ the winter by migrants from above. These 



^^^^B. latter mainly affect the trunk below the 



iflPJj^ surface soil, and these may and do return in 



spring to become the aerial race. Moreover, 



the actual root form migrates to the trunk. 



vVs far as I have observed, this migration 



is not at any fixed period of time, but is 



spasmodic. 



The damage done by the root form in 

 this country is certainly severe, but not to the same extent that it 

 is in parts of America. Stedman (1), in his most excellent work in 

 tracing this insect's life-history, shows that in Missouri it is the 



OVUM OF WOOLLY APHIS AND 

 SHRIVELLED SKIN OF 9- 



((ireatly enlarged.) 



