Galls caused by the larvae of Diplosis tremulae Wtz. 



the petioles of leaves of Populus tremula Linn. 

 PLATE 94. 



Synonymy of Insect. 



Tipula populea Schrank. 



Cecidoviyia polyiiiorpha Bremi. 



Diplosis trenmlcB Theobald. 

 Habitat of the Aspen. — This tree grows well in coppices, 



woods, and forests ; it may also frequently be seen in a 



flourishing condition on the outskirts of a wood by the 



side of a stream. 

 The Gall is formed by a continuous and rapid accumulation 



of vegetable cells resulting from the irritation to the 



tissues caused by the presence of the larva. 



Position.— On the petiole. 

 Manner of Growth.— Singly ; glabrous. 

 Colour. — Green, suffused with pink or purple. 

 Average Dimensions of a Mature Specimen (globular 

 form). 



Girth, 24 mm. 

 May be sought during the months of June to October. 

 The Growth is complete by the end of July. 

 The Typical Condition of the gall is unilocular and 



unilarval. 

 The Larva pupates in the ground. The imago emerges 



during the spring. 



These galls are very irregular as regards both their size and 

 their contour. They very rarely occur more than three on one 

 petiole. They may be situated at the axil or so far up that 

 the swelling is merged into the base of the mid-rib of the leaf. 

 Young aspen-trees are the best on which to search for them. 

 They are scarce in some districts, and do not occur at all in 

 others. They are very local anywhere ; nowhere are they 

 abundant. See also plate 117. 



The illustration is of specimens gathered at Hastings by the 

 author. 



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