354 FOREST ENTOMOLOGY. 



Hormomyia (Oligotrophia) piliger, Lw. 



The larvae of this insect cause galls on the leaves of the beech 

 (Fagus sylvatica). The galls (fig. 330) 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 larvae pupate within the gall. 



Hormomyia (Oligotrophus) capre;e, Wtz. 



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

 compared to an eruption arising from a sting on the midrib of the 



Fig. 330. Galls on upper surface of beech leaves Fig. 331. Leai-es of goat willow galled 



caused by Hormomyia piliger. by Hormomyia capreae. 



leaves of Salix eapvea (fig. 331). 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 (Mikiola) 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 



