DIPTERA. 



367 



HORMOMYIA (OlIGOTROPHUS) PILIGER, Lw. 



The larvfe. of this msect cause galls on the leaves of the beech 

 (Fagus sijlmtica). The galls (fig. 338) are pilose, more or less gregari- 

 ous on the upper surface of the leaf, but as a rule generally arranged 

 near the midrib. The colour is somewhat variable — at first yellowish, 

 then gradually deepening to various shades of red or brown. They 

 may be found from the beginning of July right on to the end of the 

 summer. The larvte pupate within the gall. 



HuR.MOilYIA (OlIGOTROPHUs) CAPRE.E, Wtz. 



This is a pustule-forming gall, as it were, inasmuch as it may be 

 compai'ed to an eruption arising from a sting on the midrib of the 



Fig. 33S. — Galls on upper surface of beech leaves 

 caused by Hormomyia piliger. 



Fig. 33ti. — Learns of goat willow rjailed 

 by Hormomyia caprese. 



leaves of Salix caxirea (fig. 339). The midrib itself is more or less 

 conspicuous, while the gall is simply the adjoining portion of the leaf, 

 transformed into a hard woody structure. The colour varies from 

 pale-green to pale-yellow. It may be found from June to October. 

 The larvae pupate in the ground, and the flies emerge during the 

 spring. 



Hormomyia (Miiciola) fagi, Hartig. 



The gall is formed on the upper surface of the leaf, and is a 

 glabrous cone - shaped structure about 4 mm. high. The colour 

 varies from green to yellow, and reddish. It may be found from 



