Galls caused by the larvae of Urophora cardui Linn. 



on 



the stems of Carduus arvensis Curt. 



PLATE 33. 



Synonymy of Insect. 

 Trypeta cardui Linn. 



„ Walker. 



Habitat of the Creeping Thistle. — Grows in fields, on 

 hill-sides, waste places, semi-cultivated places, etc., in 

 sheltered and exposed situations abundantly all over 

 Britain. 



Position. — At the top of the stem and also at the nodes. 



Manner of Growth.— Singly ; glabrous, glossy. 



Colour. — Pale green, becoming darker with age. 



Average Dimensions of a Mature Specimen. 

 Height, 24 mm. ; girth, 70 mm. 



May be sought during the months of July, August, September. 



The Growth is complete by the end of August. 



The Typical Condition of the gall is plurilocular. Usual 

 number of cells, 4. 



The Larv/E pupate in the gall. The imagines emerge during 

 May and June. 



The operations of the larvas of this species are in keeping 

 with those of Uropltora solstitialis. They develop from the 

 ova simultaneously with the unfolding of the apical portion 

 of the thistle, when it is about to produce the flowers, and 

 arrest its further upward growth. The ascending sap accumu- 

 lates and gives rise to a large bulbous swelling, which the 

 larvae eat into in a downward direction. The apertures of 

 the galleries remain open, the fras, however, being allowed 

 to remain in them. 



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