Galls caused by the larvae of Cecidomyia betulae Wtz. 



on 



the staminate catkins of Betula alba Linn. 



PLATE 120. 

 Synonymy of Insect. 



Habitat of the Common Birch.— Plentiful all over Britain 

 in parks, plantations, woods, and gardens. 



The Gall is formed by the larva feeding upon portions of 

 the catkin and preventing its full and complete development. 



Position.— The catkin itself forms the gall. 



Manner of Growth.— Deformed; curved; constricted; dwarfed. 



Colour. — Reddish brown, chocolate-brown, black. 



Average Dimensions of a Mature Specimen. 

 Length, 20 mm. ; girth, 12 mm. 



May be sought during the months of October to May. 



The Growth is complete by the end of April. 



The Typical Condition of the gall is unilarval. 



The Larva pupates in the gall. The imago emerges during 

 April. 



These galls are very abundant. Some trees, especially 

 young ones, are very badly attacked. In the spring, as soon 

 as the catkins begin to develop, the larvae commence their 

 attacks, and cause distortions and deformities which are more 

 or less uniform in character. Some specimens are so completely 

 eaten through that the distal portion falls off, leaving a mere 

 stump on the twig. Such a specimen is shown on the right- 

 hand side of the illustration. Others shrivel, end in a point, 

 turn black, and remain sterile. 



The illustration is of specimens gathered at Hastings by 

 the author. 



