Galls caused by the larvae of Cecidomyia rosarum 



Hardy 



on 



the leaves of Rosa canina Linn. 

 PLATE S7. 

 Synonymy of Insect. 



Cecidomyia rosce Macq., Biemi. 

 „ rosarum Theobald. 



Habitat of the Dog-rose. — This is the commonest rose in 

 Britain ; it grows rapidly and luxuriantly in hedges, thickets, 

 and various dry places in every part of the country. 



The Gall is formed by the edges of the leaflet rising above 

 the mid-rib until they approximate and a thin-walled, 

 hollow pod is formed. 



Manner of Growth. — Glabrous ; glossy ; furrowed exterior 



Colour.— Green externally, reddish brown internally. 



Average Dimensions of a Mature Specimen. 



Length, 30 mm.; breadth, 6 mm.; girth, 18 mm. 



May be sought during the months of June to October. 

 The Growth is complete by the end of August. 

 The Typical Condition of the gall is multilarval. 

 The Larv^ pupate in the ground. The imagines emerge 

 in about six days after pupation. 



These galls may be found on the same rose-bushes as 

 Rhodites rosce, R. eglaiiterice, and R. nen'osus ; but it is rare 

 to find either of the latter two species on a leaf conduplicated 

 by C. rosai-uvi. The juncture of the edges of the leaf is very 

 perfect, and the larvae, which sometimes number fifty, are 

 unable to get out. At the part where the edges meet a 

 slight viscousness is frequently noticeable. At the approach 

 of autumn the edges gape, and the larvae fall to the ground 

 to pupate. 



The illustration is of specimens gathered at Hastings by 

 the author. 



