DIPTERA. 



353 



Diplosis (Harmandia) tremul^e, Wtz. 



Theobald says : " The larvte of the ' aspen gnat ' seem to form two 

 kinds of galls : the first are formed on the leaves of Pojpulus tremula 

 these are red galls, the size of a pea ; the second kind is the well- 

 known gall formed on the leaf-stalk : each gall is inhabited by a 

 single larva, which pupates in the ground (Winnertz)." 1 



I found what I now suspect to have been the first form, in June 

 1897, in High Legh, Cheshire, but the latter I have never found, and 

 am indebted, to Mr E. T. Connold for the form as shown in fig. 329. 



Fig. 329. Galls on leaf-stalks of aspen -poplar caused by Diplosis tremuUe. 

 (From photo by E. T. Connold.) 



Theobald thus describes the fly : " Imago -dorsum blackish-brown, 

 with two rows of whitish-yellow hairs ; abdomen dark-brown, with 

 thin flesh - coloured incisions and white hair. Posterior half of 

 seventh ring and the rest of the abdomen flesh-coloured ; genitalia 

 black ; yellow. Wings large, grey, with thick blackish-grey hairs, 

 third longitudinal vein bending in an almost straight angle to the 

 posterior edge; 1 to H lin." 



1 An Account of British Flies, by Fred. V. Theobald, p. 75. 



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