HYMENOPTERA. 



21 



has been clearly shown to exist amongst the Cynipidai. It is a remarkable fact, 

 too, that the galls produced by a parthenogenetic female are different in form from 

 those produced by a female originating from the normal sexual process. The 

 insects produced by these different galls were for many years looked upon as 

 distinct species. It is, of course, on the cell-tissues of the gall that the larvae of 

 the Cynipidce feed and thrive ; they themselves, however, in their turn being 

 subject to the attacks of numerous hymenopterous parasites of various kinds. 



Of the typical genus, we may take the common oak-gall wasp (Cynips folii) 

 as a familiar example. It is a glistening black insect, which forms an oak-gall on 

 the under side of oak-leaves. A parasite (Torymus 

 regius) lays its own egg upon the larva of the 

 Cynips lying within the gall, when the latter is 

 about half grown. Another species (Cynips gemmce) 

 is produced from conical scale-covered galls, sprout- 

 ing from the young shoots of the oak, in the interior 

 of which the grubs feed. The illustration on p. 20 

 shows the gall produced by insects of this species. 

 To the same family belongs the sponge gall-wasp 

 (Teras terminalis), .which emerges from many- 

 chambered spongy galls. In spring these galls are 

 light coloured ; but later on, when the insect has 

 made its escape, become brown. The female insects 

 may be either winged or wingless, whereas the males 

 are always provided with these appendages. Up- 

 wards of forty parasites have been reared from the 

 galls of this species. Yet another familiar type is 

 the bramble gall-wasp (Diastrophus rubi), which in 

 spring produces hard and often twisted swellings on 

 bramble -stems, from which in due course emerge 

 the perfect insects. In the same illustration is 

 shown the oak - root gall - wasp (Bioriza aptera). 

 In this form the female is wingless, but the male is 

 unknown. The galls are formed on the rootlets of 

 the oak-trees beneath the surface of the ground. 



In the common rose-gall wasp (Rhodites rosce), which produces the so-called 

 bedeguan gall on roses, the larvae are full-fed in autumn, although the perfect insect 

 does not appear till the following spring. Their beautiful, mossy, pink-tinted galls 

 furnish a home for many other insects, such as various species of Synergus, but 

 especially parasites belonging to the families Pteromalidce and Braconidce. 

 Synergus facialis, of which a figure is given in the lower illustration on p. 20, is 

 parasitic on the gall-wasps. So too is Figites scutellaris, shown in Fig. 6 of the 

 same illustration. These are gall-wasps, so far as structure is concerned ; but as 

 regards their habits they are in no way different from ichneumons, living in the 

 larval state in the bodies of various insects. Figites scutellaris, as well as most 

 other members of the group, are parasitic on the larvae of the flies ; while Ibalia 

 cultellator is parasitic in the larvae of the giant saw-flies. 



ROSE GALL-WASP AND ITS GALL. 



