132 



THE CULTIVATED EVERGREENS 



young lice crawl to the tender growth where they station 

 themselves on the leaves which have already begun to 

 show indications of the developing gall. The formation of 

 the gall is apparently initiated by the feeding of the parent 

 plant-louse. As the gall increases in size, the leaf tissue grows 

 over the young aphis which thus comes to occupy a closed cell. 



Within this retreat the aphid 

 passes through four stages; the 

 cell then opens and it escapes. 

 This usually takes place in 

 August. At the last molt the 

 plant-louse acquires wings and 

 then takes her position on a 

 spruce leaf where she deposits 

 a cluster of eggs, leaving her 

 dead body over them as a protec- 

 tion. On hatching, the young lice 

 scatter over the nearby branches and attach themselves to 

 the leaves and in crevices around the buds. It is in this condi- 

 tion that the insect passes the winter. 



It is thought by some that the life history of the insect is 

 not as simple as is indicated above but that there is a regular 

 migration from spruce to larch and from larch to spruce. It 

 is quite probable that a migration does take place when both 

 kinds of trees are growing near each other. In cases in which 

 larches are not present, the insect seems to be capable of 

 breeding indefinitely on spruce. 



The spruce gall aphid can be controlled effectively on 

 ornamental plants by thoroughly spraying with whale-oil 

 soap — one pound in two gallons of water. The application 

 should be made during the winter or in early spring before 

 new growths start. A miscible oil — one part in twenty of 



15. Spruce gall aphid on larch. 



