14 LEAF-MINING INSECTS 



Between typical linear and blotch mines there are all 

 sorts of intergradations. Often a linear mine expands 

 suddenly and broadly; then it is called linear-blotch. Some- 

 times a mine starts in linear form and widens gradually to 

 flaring margins; then, on account of its outline, it is called a 

 trumpet mine. 



Many mines start in linear form and become blotched 

 through winding, and intercrossings and cutting out of all 

 the mesophyll between passage ways that were at first 

 separate; but blotches are regularly formed by systematic 

 peripheral excavation, which may be made irregularly or all 

 around or in one general direction only or alternately at 

 opposite ends, or by back and forth "swath cutting' ' across 

 one end. The boundaries of both linear and blotch mines 

 are generally determined in part by the impeding larger 

 veins of the leaf. 



2. As to depth, mines may extend from upper to lower 

 epidermis, full depth mines, or they may occupy only the 

 uppermost or the lowermost layers of the mesophyll, in 

 which case they are called upper surface and lower surface 

 mines, respectively. Only the full depth mines are equally 

 visible from both sides of the leaf. 



A few linear mines run irregularly through the mesophyll, 

 some of them, while small, appearing first on one surface 

 of the leaf, and then on the other. Most mines become 

 deeper as the size of the larva increases. The terms used in 

 descriptions, unless otherwise stated, apply to completed 

 mines. The very common miners of the genus Lithocolletis 

 make a very shallow surface mine during the first three 

 larval instars, completed as to area by that time, and then 

 excavate the remaining mesophyll during the next two 

 larval instars, leaving when completed a full depth mine. 



3. As to finish, mines may be open or closed. The larvae 

 of moths of the genus Cosmopteryx, Lyonetia and other 

 genera maintain as an open door a hole in the epidermis 



