Andnciis noduli. 31 



5^. Andricus noduli. Hts:-^ 



Gall. The gall is scarcely 2 mm. long, and lies 

 within an oak-shoot of that year's growth, but is often 

 only recognizable from without by small round eleva- 

 tions of the bark. The mature galls form hollow 

 cavities in the substance of the wood, lined with thin 

 membranes. They are not unfrequently found in the 

 leaf stalks, which then appear thickened and swollen. 

 They give rise to more or less deformity (see Fig. 5 a). 



Rearing the Fly. To obtain the flies with certainty 

 the shoots on which the galls are formed should not 

 be collected too long before the flight time, otherwise 

 the wood is apt to become too dry. The time when 

 the flies emerge is variously stated, but I have con- 

 vinced myself by many experiments that they begin 

 .early in August and go on to the middle of that 

 month. 



It may, however, happen that a few flies do not 

 appear until the next year, these may come from late 

 individuals of Aphilotrix radicia, but in any case they 

 are a small minority. 



Fly. Size, 2 mm. ; males and females differ in 

 colouring. 



Female. Thorax black, dull, sometimes streaked 

 with orange; abdomen orange with a black blotch 

 on the back of the first segment ; the tip of the ab- 

 domen and ventral sheaths black. Legs testaceous, 

 the hind coxae dark ; antennae dark, at the base 

 testaceous. 



P Andncus trilineatus, Htg. Andricus radicis, sexual form, Cameron.] 



