358 FOREST ENTOMOLOGY. 



The gall is formed, through the agency of the cambium, on the side of 

 the twig. Growth is complete in September ; the larva pupates in 

 the ground, and the fly emerges in spring. 



Family PHYTOMYZID^E. 



In this family the larvae are leaf-miners, and, so far as the species 

 to be considered are concerned, they pupate within the leaf. The 

 puparia are barrel-shaped. According to Eev. W. J. Wingate, there are 

 several genera and species in the north of England, but as regards 

 identification of species and association with damage I have only 

 hatched two species. 



As the species on snowberry leaves makes markings very much 

 after the manner of the larva? of several micro-lepidoptera, it would be 

 well for the student not to be over-sanguine in naming insects from 

 markings without verification by hatching. It would be well to bear 

 in mind, also, that in those species where pupation takes place within 

 the epidermal skins of the leaf, specimens should not be placed within 

 the hatching-box until the creature has reached the pupal stage. 



Chromatomyia obscurella, Fin. 

 Phytomyza xylostei, Kalt. 



The leaves of snowberry (Symplioricarpus racemosus) are often 

 thickly covered over with white trailing galleries, as in fig. 337. In 

 fact, in several parts of Northumberland in some patches this species 

 is so common that it was almost impossible to get a leaf without 

 markings. 



The insect causing this damage has a double generation in a year. 

 The first generation appears in spring, probably in May, and the larval 

 markings appear in June. At first the larva moves very irregularly 

 around a common centre, but afterwards it " mines " more rapidly, 

 making long winding galleries. The larvae pupate within the leaf, 

 and the flies appear in the last week in July. The flies of this brood 

 immediately deposit eggs on the leaves which have developed during 

 the summer, and the larvae make similar markings to those of the first 

 generation, and pupate within the leaves, which of course fall to the 

 ground in autumn. 



The flies, which are like small house-flies, are matt black. Eyes 

 dark red, wings hyaline. 



