16 LEAF-MINING INSECTS 



operations may be confined to a small territory or may 

 cover the entire leaf. 



Leaf-mining caterpillars spin less silk than do most other 

 moth larvae, but even within the mines silk may serve a 

 variety of uses, such as lining the mine (Tischeria), tying 

 up frass pellets out of the way, and making cocoons. Some 

 highly specialized leaf-miners, notably species of Litho- 

 colletis, increase the space within the mine by spinning 

 silken threads across the loosened epidermis. These threads 

 on drying contract and the mine is thrown into wrinkles 

 or into a single roof -like fold. It is then called a tentiform 

 mine. Many details of spinning habits will be found in the 

 chapter on Lepidoptera under the several species, each of 

 which spins in its own way. Mines may further differ in 

 size, in smoothness and color of surface, in transparency, 

 and in manner of frass disposal. This last will often give a 

 clue to the relationships of the larva within the mine. 

 Sap-feeding larvae of the Lepidoptera have little solid 

 matter in their food and hence there is not much frass 

 deposited in their mines, and that little is rarely in the 

 form of distinct pellets. Tissue-feeders, on the contrary, 

 consume quantities of indigestible cellulose cell walls, and 

 reject the cellulose generally in distinct pellets, that are 

 often very considerable in amount and may even seem 

 almost to fill the mine. The manner of bestowal of the 

 frass — whether in central or peripheral midden-heaps or 

 lines, or irregularly, is often characteristic of particular 

 species. It is a very small flat that leaf-miners occupy, and 

 their housekeeping problems are serious. All of the more 

 specialized among them have ways of maintaining free 

 working space and of keeping their food clean. 



MINING OPERATIONS 



The feeding operations of many leaf-mining larvae may 

 be readily observed with a good lens, holding their leaf up 



