Galls caused by the larvae of Cecidomyia sisymbrii Schrk. 



on 



the stalks of Sisymbrium officinale Scop. 



PLATE 29. 



Synonymy of Insect. 



Cecidomyia barbai-ea Curtis. 



„ sisymbrii Theobald. 



Habitat of the Hedge-mustard.— This plant grows to 

 the height of from i8 in. to 30 in. in hedges and by road- 

 sides, but less when in waste places and open situations. 

 Abundant throughout Britain. 



The Gall is formed by the larvze causing a cessation of 

 upward growth and a consequent crowding together of 

 flowers and seed-pods. 



Position.— At the termination of the shoots. 



Manner of Gro\vth. — Singly ; glabrous. 



Colour. — Slightly paler green than other portions of the plant. 



Average Dimensions of a Mature Specimen. 

 Height, 15 mm.; girth, 30 mm. 



May be sought during the months of June, July, and August. 



The Growth is complete by the end of July. 



The Typical Condition of the gall is multilarval. 



The Larv^ pupate in the gall. The imagines emerge during 

 the autumn. 



It is not improbable that the imagines which emerge during 

 the months of September to November oviposit in some other 

 plants, and that the larvae therefrom remain in the galls they 

 then cause until the following June. 



The illustration is of specimens gathered at Guestling, near 

 Hastings, by the author. 



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