OF EPPING FOREST- 27I 



Gall vanation. 



As before mentioned galls of different generations of the 

 same species often occur on different parts of the oak besides 

 varying in shape and colour, etc. Galls of the agamic genera- 

 tion, Diyophnnta folii, the common Cherry-galls of the oak, occur 

 on the back of the leaf while the corresprmding galls of the 

 sexual generation, D. taschenbergi, usually arise from adventitious 

 buds situated on the trunk of the tree. The former when 

 mature are large, round, yellowish galls, often with a red cheek, 

 the latter are very small velvety galls, purplish in colour, hardly 

 noticeable against the bark. 



The great difference between the galls as they occur on the 

 oak, and the similarity existing between the insects which 

 form them, is very marked, The larvae are fleshy, legless grubs, 

 usually white or yellowish in colour. The perfect insect is, as a 

 rule, brown or black, and it is almost impossible to find sufficient 

 variation to differentiate between the species in some cases. 

 Those agamic forms having only one generation a year, such as 

 Andvicus qiiadnlineatns and A. seminaticnis, are practically identical, 

 and yet the galls are very different. This may be accounted for 

 by the fact that the larva is surrounded by the gall tissue 

 throughout its whole life, and is never exposed to the light, so 

 cannot be acted upon in any way hy external influences, and 

 consequently varies but little. The perfect insects live only a 

 short time and die as soon as the eggs are laid. The galls on 

 the other hand serve to protect the larvae from parasites, and 

 are, therefore, greatly modified by external conditions. 



Inquilines and Parasites. 



The number of parasites and inquilines preying on the gall- 

 makers and living in their galls is enormous. They are of three 

 kinds : — 



Inquilines or " guest-flies " which live in the thickening of 

 the gall substance, doing no harm to the hosts. 



Inquilines which do not directly prey upon the host but 

 starve it out and take up the extra room thus obtained for their 

 own benefit (including certain Synergidae in the galls of Cynips 

 kollari.) 



Direct parasites preying on the larvae, such as Chalcididae, 

 Ichneumonidae, and Braconidae. 



