GALL- WASPS. 225 



spring it ascends and pupates in the sapwood, and between July and 

 September emerges from a straight round hole (generation 2 years or 

 more). 



The Large Yellow Wood-wasp, Sirex gigas, mostly attacking Spruce, 

 Stiver Fir, and Larch, is blackish, with a yellow patch behind each eye ; 

 and in the ?, l^ in. long, the first 2 and the last 3 segments of the 

 abdomen are yellow ; while in the smaller <5 all are reddish-yellow, except 

 the first and the last, which are black. The Steel-blue Wood -wasp, 

 Sirex juvencus, bores chiefly in Pine and Larch. The ? , 1^ in. long, has 

 a steel-blue body with reddish legs, while the 6 is smaller and has 

 yellowish-red rings from the fourth to the seventh abdominal segments. 

 Extermination consists merely in cutting out sickly or damaged stems 

 and thinning the woods properly. 



C. GALL- WASPS (Cynipidce) have fore-wings with 6 or 8 bays, 1 long at 

 apex and 2 or 3 rhomboidal at edge, but sometimes only aborted wings, 

 or none at all ; <$ usually much smaller than 9 . Larvce generally thick, 

 fleshy, smooth, whitish, and incurved. Pupce thick, smooth, and 

 whitish. Many species have an intermediate sexless form, also laying eggs, 

 which hatch out insects differing in appearance and habits from those 

 issuing from sexually fertilised eggs. The commonest kinds are the 

 Oak-apple Gall-wasp, Cynips querci, forming red and green galls about 

 cherry-size on the lower side of oak-leaves, and the Marble Gall-wasp, 

 C. Kolla,ri, on young oaks in nurseries. 



IV. TWO-WINGED INSECTS (Diptera). 



The injurious insects of this order are the gall-gnats (Cecidomyidce), the 

 chief being the Large Osier gall-midge Cecidomyia salicis, f in. long, 

 blackish, long-legged, with red-ringed, whitish-haired abdomen, which 

 lays eggs on osier-shoots in May and July, hatching out into reddish- 

 yellow maggots that spoil the rods by causing spindle-shaped nodes, in 

 which pupation takes place ; the Small Osier gall-midge, C. saliciperda, 

 T V in. long, with black-brown body and white wings, appearing in May, 

 and doing similar damage ; and the Osier shoot-tip gall-midge, C. hetcr- 

 obia, forming galls on the terminal shoots. Extermination, cutting off 

 and burning infested twigs. 



V. HALF-WINGED INSECTS (ffemiptera). 



The class Homoptera, having fore- and hind-wings alike, includes the 

 often very destructive Plant-lice and Scale-insects, which rapidly multiply 

 enormously without any distinctly marked metamorphosis, the larvse 

 moulting several times and the wings being freed at the last moult. 



Among the Plant-lice (Aphidce}, by far the most injurious is * the 



P 



