GALL WASPS 



2983 



special portion of the plant for its attack, which it pierces with its ovipositor, and 

 lays an egg in the wound. As to what exactly gives rise to the resultant gall, 

 which follows sooner or later upon the wounded plant, is not known with any cer- 

 tainty. It has hitherto been supposed that the fly injects an irritating fluid into 

 the wound, but recent researches tend to show that this serves rather as an adhesive 

 security to retain the egg on the selected spot. It is probable that the different 

 stimulative irritants offered, first by the inflicted woand, next by the presence of 

 the eggs, and thirdly by the movements of the larva after it is hatched, together 

 with the action of a fluid exuded by the grub itself, all tend to produce the strange 

 modifications of cell structure which manifest themselves in the forms of the 

 various kinds of galls. The larvae of the Cynipidce almost entirely feed internally 

 upon galls produced on oak leaves and the oak blos- 

 soms. These galls are entirely closed, and the grub 

 dwells within a hard cell, called the larval chamber. 

 In some cases there may be several such chambers, 

 as, for instance, in the Bedeguar gall on the wild 

 rose tree formed by Rhodites ros<e. We have said 

 that each species confines itself to one portion of the 

 plant, and the form of the gall is the same; but an 

 exception is furnished by the galls of Spathegaster 

 baccarum, which occur upon the leaves as well as on 

 the flower tassels of the oak. 



The phenomenon known as the alternation of 

 generations, that is to say, where produced genera- 

 tions alternate with each other in consecutive suc- 

 cession, has been clearly shown to exist amongst 

 the Cynipidce. It is a remarkable fact, too, that the 

 galls produced by a parthenogenetic female are dif- 

 ferent 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 them- 

 selves, 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 ( Cynipsfolii} 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, 

 sprouting from the young shoots of the oak, in the interior of which the grubs feed. 

 The illustration on p. 2982 shows the gall produced by insects of this species. To 

 the same family belongs the sponge gall wasp ( Teras terminalis) , which emerges 



ROSE GALL WASP AND ITS GALL. 



