Biorhiza apt era. 71 



IV. Biorhiza Group ^ 



17. Biorhiza aptera. Fbr." 



Gall. This gall is formed only on oak roots, and on 

 the smallest as well as on the thickest. When it first 

 bursts through the cortex it is soft and of a pink colour, 

 but at maturity it becomes brown, hard and woody. 

 The galls vary much in size, the smallest being about 

 the size of a pea. They are rarely isolated, and are 

 usually united into a large mass. (Fig. 17.) 



Owing to their obscure situation it is not easy to 

 procure the galls, but the flies may be collected when 

 they appear on the oak. The time given by different 

 authorities for their appearance varies, some having 

 found them in November, and some in March ; according 

 to my own observations the latter date must be con- 

 sidered as exceptional, at least in this place. I have 

 for many years found the flies regularly in the end 

 of December and beginning of January. 



Fly. Size 4-7 mm. long ; wingless ; thorax slender, 

 pilose at the sides ; the whole insect yellowish brown ; 

 the abdomen darker, with an almost black transverse 

 band across its middle; legs of same colour; size of the 

 fly very variable. 



Experimental breeding. I have made many attempts 

 at breeding with Biorhiza aptera, and I was very soon 

 satisfied that the flies do not go to the roots of the oaks 

 to deposit their eggs, but rather try to ascend by 



[ ^ Biorhiza^ Westwood. Apophyllus, Hartig. Teras, Hartig. Dryo- 

 teras, Foerster. 



^ Cynips aptera, Fab. ; Biorhiza terminalis, agamous form, Cameron.] 



