86 FORESTRY 



with the hand, but it is impossible to cope with the pest in 

 older woods. 



Hemiptera 



SPRUCE-GALL APHIS, Chermes abietls. After wintering under 

 scales in the bark, the so-called " mother " aphis appears in 

 spring. She pierces into the twigs 

 of the Spruce, and through irritation 

 thus caused a cone-like gall (Fig. 19) 

 arises. Here eggs are laid amongst a 

 woolly secretion, and the tiny aphides 

 coming from these suck the juices of 

 the gall, which, from being quite in- 

 significant, increases to the size of a 

 small pine cone. The aphides become 

 enclosed in the gall, where they oc- 

 cupy cells or chambers until full- 

 grown in August. At that time the 

 galls turn to a brown colour, and the 

 chambers split open, allowing the 

 green-fly to escape. If Larch be at 

 hand, some of them fly to it and de- 

 posit eggs ; from these a female form is 

 hatched, which seeks protection under 

 scales of the bark during winter. 

 This is the " Larch aphis," Chermes 

 lariciS) so well known in connection 

 with Larch canker. 



LARCH APHIS. With the arrival 

 of spring the wingless females creep 

 FIG. 19. GALL FORMED BY from their wintcr shelters, and lay 

 SPRUCE-GALL APHIS eggs on the twigs of the Larch. 

 ( Chermes abietis} The chermes from these are covered 



with a white woolly down. Both 



they and the parent form settle upon the needles, which 

 they pierce and suck, weakening them and causing them 

 to bend angularly. The appearance of the trees is as 



