138 LEAF-MINING INSECTS 



then on the other, and their position at the time of feeding 

 being transverse to the course of the mine. The excrement 

 on this account comes to be arranged in two black lines 

 one at either border of the mine its whole length. 



There are usually two generations annually of species of 

 the Cameraria group, though there may sometimes be but 

 one. The summer brood pupates as follows: its mine re- 

 mains flat until the seventh instar. Then as the larvae 

 approach pupation they spin a small amount of silk upon 

 the loosened epidermis, which by contraction causes one to 

 three narrow folds or ridges. Beneath these folds the larva 

 spins a thin sheet of silk over a part of the floor and then 

 lying on its back spins over itself a flat semi-transparent 

 sheet of silk, oval or nearly circular in shape and attached 

 around its edges to the silk-strewn patch below. The larva 

 then comes to rest under the long axis of the cocoon and 

 presently transforms to a pupa. Before the adult escapes 

 the pupal shell is thrust through a transverse slit at one end 

 of the flat cocoon and through the upper cuticle of the leaf. 

 The generation emerging in early summer has overwintered 

 as larvae. In some species, hibernation takes place under 

 the folded epidermis but in most species an especially pre- 

 pared silk-lined chamber is formed. Oval or rounded silken 

 patches are spun upon corresponding areas to form a unique 

 chamber of silk and cuticle. On the upper side of the leaf 

 it appears as a flat, smooth circle, on the lower as an oval 

 or hemispherical projection. The change to a pupa occurs 

 in the spring. 



In choice of host plants in this group resembles that in 

 the group of Lithocolletis proper very strongly. All the 

 recorded host plants of North American species are broad- 

 leaved woody plants. Thirteen species are attached to the 

 oak group, four to the birch family, and the eleven other 

 species whose hosts are recorded are distributed to eight 

 other families containing woody plants. 



