Galls caused by the larva; of Urophora solstitialis 

 Linn. 



on 



the flower-heads of Gentaurea nigra Linn. 

 PLATE 125. 

 Synonymy of Insect. 



Trypcta solstitialis Linn., Walker. 



Habitat of the Knap-weed. — This ubiquitous plant 

 flourishes in a great variety of situations, meadows, 

 pastures, hillsides, and hedgerows being among its 

 favourites. 



The Gall is formed by the larvae feeding upon the de- 

 veloping seed thus causing it to increase abnormally in size 

 and become abortive. 



Position. — Concealed within the flower-head. 



Manner of Growth. — Singly ; thickly covered (except at 

 its base) with long greyish hairs. 



Colour.— Brown. 



Average Dimensions of a Mature Specimen. 

 Height, ID mm. ; breadth, 8 mm. ; girth, 20 mm. 



May be sought during the months of August to June. 

 The Growth is complete by the end of October. 



The Typical Condition of the gall is plurilocular. Usual 



number of cells, 3. 

 The Larv^ pupate in the gall. The imagines emerge 



during June. 



The imagines are not difficult to rear. If the flower-heads 

 be gathered in October and kept in a small bag of leno and 

 hung up in a summer-house or out-house, the flies will emerge 

 during May or June of following summer. The proportion of 

 male and female imagines is about equal. The galls are as 

 ubiquitous as the plant itself, and 25 per cent of the heads of 

 every affected plant will contain galls. 

 2S3 



