64 LEAF-MINING INSECTS 



the silk carpeted floor, others, in a special cocoon attached 

 to the upper surface. In the large genus Lithocolletis, in 

 so far as habits are known, all our species but one (L. 

 osteiisackenella) pupate in the mine. 



All the forms of mines mentioned in our introduction 

 (p. 12) are made by Lepidoptera. There is a general 

 correlation between the type of mine and the genus. There 

 is also probably a correlation between the form of the larva 

 and the form of mine, Nepticulae, as a rule, make linear, 

 serpentine mines which later may or may not become 

 blotches. Phyllocnistis always makes a very long, tortuous 

 linear mine which does not become a blotch. Bucculatrix 

 always makes a linear serpentine mine during its early life. 

 It is interesting to note that these three have structures 

 w T hich would seem well adapted for forward movement: 

 These feed in arcs, swaying the anterior part of the body 

 from side to side and getting some impact against the 

 parenchyma by alternately stiffening and relaxing the body. 



There are differences among mines that are perhaps more 

 significant than that of superficial shape. Of linear mines, 

 for instance, those of the genus Phyllocnistis can almost 

 surely be identified at sight. This is a genus of sap-feeders 

 and practically none of the parenchyma is removed but the 

 superficial layer of these cells is sheared through and the 

 liquid contents sucked up. In this respect the mine does 

 not change from beginning to end. On account of the liquid 

 diet the mine is affected in several ways. In order to collect 

 enough food from sap alone to make a whole moth, be it 

 ever so small, it is necessary to use quantities of the sap 

 and, therefore, the mine is very long indeed. Then so little 

 of the leaf substance being removed, there is almost no 

 difference in transparency between the mined area and the 

 remainder of the leaf. Then the castings, if they show at 

 all, do so only by reason of their changed color or because 

 they make the cuticle to adhere again to the parenchyma 



