1 70 THE OAK GALLS AND GALL INSECTS 



gradually getting rid of wings which are of no service to them 

 and are even a hindrance when laying their eggs in the roots of 

 the tree. 



(26). — Agamic Generation. I. Trigonaspis renum (Htg.) 



Inquiline. Synevgus thaumacera (Dal.) 



Gall. 



The galls are situated on the back of the leaf, usually there 

 are a great number on each leaf. They are small irregular galls- 

 very often kidney-shaped, but the form varies. Greenish white 

 to red in colour, becoming brown later, when mature, unless 



parasitised. They are arranged along the leaf veins. 



Imago. 



Colour : Brownish to yellowish red. Antennoc : Thirteen-jointed. lliorax :. 

 Punctured, dull ; scutellum : hair\'. Abdomen : Shining, vertex shagreened ; 

 almost sessile. Legs : Lighter yellow than the body ; claws : simple. Wings : 

 None. 



(26.) — Sexual generation. Ia. Trigonaspis crustalis 

 (Htg.) 



Inquilines. Synevgus thaumacera (Dal.) 5. facialis and 5. 

 paUicov?iis (Htg.) 



Gall. 



Appears from adventitious buds near the base of the oak 

 trunk, on shoots growing from the trunk, or on shoots growing 

 out of the ground from acorns dropped from the trees. Shape : 

 Globular, size variable. Apex sometimes pointed. Colony : 



White, \ellowish white, pink, or bright red. 



Imago. 



Colour: Black (abdomen, red), shining. Antennae : Dull reddish brown at the 

 base, darker towards apex. Thorax : Black. Head : Black. Abdomen : Red 

 or bright orange, shining, distinctly pedunculate. Legs : Orange, base ot coxae 

 infuscated. Wijigs: Long and well developed, clouded in front of the cubitus 

 and often at the base of the radial cellule. 



Account of the Generation Cycle. 



The flies from the Trigonaspis renuni galls appear in December 



and January, though sometimes later. The eggs are laid in the 



adventitious buds on the tree trunks, or on buds on young stems.. 



In April the small red gall of Trigonaspis crustalis appears, but in 



cases where oviposition has taken place later, these galls do not 



form until as late as the middle of May. From the end of May 



imtil the middle of June the flies emerge, the females pricking 



