26 LEAF-MINING INSECTS 



(Mrs. Tothill) in Vancouver on the madrona leaf-miner, 

 Marmara arbuticlla, indicate how easy is the passage from 

 stem to leaves. In some cases the mining of a single larva 

 is confined to a single leaf ; in some cases the larva does not 

 enter a leaf at all but tunnels up and down under the cuticle 

 of the shoot. In many cases, however, the mines either 

 begin in the leaves and pass by way of the leaf petioles down 

 under the epidermis of the shoots, or, beginning under the 

 epidermis of the shoots pass up the petioles into the leaves. 

 In a few cases the mine begins in one leaf and passes by way 

 of the petiole into the shoot and then up another petiole 

 into another leaf. The surface of green apples is some- 

 times mined by another species of Marmara (M. pomonella, 

 (fig. 4, pi. 2) ; and the phyllodia of prickly pears (species of 

 Opuntia), by the larger larvae of the Phaloniid moth, 

 Melitara prodenialis. In the chapter on Lepidoptera a 

 number of examples will be cited 4 of moth larvae that mine 

 the blade of the leaf while very small, and the strong veins 

 and stalk when older and larger. The natural cavities of 

 seme leaves provide a home for certain unspecialized young 

 larvae of Noctuidae. 5 These cavities are soon outgrown. 



Feeding from shelter is often combined with leaf -mining, 

 and in a variety of ways. A leaf-tyer of the southwestern 

 United States, when it has fastened together with silk three 

 or four leaves at the summit of the wandlike stem of Bac- 

 charis viminea and has spun about itself a white silken bag 

 in which to dwell, makes a hole in the upper end of the bag, 

 where it is attached to a leaf, and eats through the epidermis 

 of the leaf and then mines the leaf through this hole. It 

 lives well up in the bag and deposits all its frass in a midden 

 heap at the bottom. It reaches out of the holes at the top 

 (one into each leaf that it mines) and feeds there without 



4 See Phthorimaea operculella, p. 159; Acrocercops strigifinitella, p. 124. 



5 See Arzama obliqua, p. 176. 



