INSECTS, DISEASES, AND INJURIES 



131 



The pitch-mass borer (Parharmonia pini, Kellicott) . 



The trunks of healthy pine trees are often disfigured by 

 large unsightly masses of gum, caused by the larvae of a beau- 

 tiful, blue-black and orange, narrow- winged moth which 

 burrows in the inner bark and sapwood. The insect sometimes 

 requires three years to complete its development. It may be 

 held in check by carefully removing the mass of pitch and 

 killing the borer in its burrow. 



Spruce gall aphid (Chermes ahietis, L.). Figs. 14, 15. 



Norway and white spruces are subject to attack by a 

 plant-louse which causes the formation of cone-shaped galls 

 at the base of the smaller twigs. These galls are about one 

 inch long and bear a striking resemblance to a small pineapple. 

 The infested twigs may die, and when the galls are numerous 

 the tree may assume a ragged and unsightly appearance. 

 Young trees are most liable to serious injury. 



The plant-louse 

 which produces the galls 

 lives over winter in a 

 partly grown condition, 

 hidden away in cracks 

 of the bark around the 

 buds. In the spring 

 these aphids complete 

 their growth and about 

 the middle of May de- 

 posit a cluster of ap- 

 proximately three 

 hundred yellowish eggs. 

 These eggs hatch in 



about a week and the h. Work of spruce gall aphid— C/termcs abietis. 



