140 LEAF-MINING INSECTS 



varies inversely with the amount of green tissue remaining, 

 until, when the whole mine is cleared, it has a diameter of 

 some 2 to 3 mm. No definite cocoon is made by this species 

 but a web of silk spun across the part of the arch away from 

 the frass-ball supports the pupae. 



The polygon miner of the linden, L. lucetiella, is rather 

 common in the Atlantic States. The mines are usually 

 bounded by two main lateral veins and by two of the veins 

 running from one to the other of these. These boundaries 

 give the mine a rectangular, often nearly square outline. 

 The larvae separate the cuticle in their first three instars 

 and in the fourth and fifth, pick out the parenchyma of the 

 area but they do not spin silk upon the separated cuticle 

 and the mine is unusual in being entirely flat. The green 

 tissue is eaten away first at the edges and then more and 

 more towards the center until w r hen the larvae stop feeding 

 the mine is either entirely clear or has but a few flecks of 

 green in the middle. All the excrement of this period is 

 pushed to the extreme borders of the mines, which when 

 complete are shining white and so transparent that the pale 

 greenish larvae can be seen very plainly. In the center of 

 the mines the larvae spin flattened oval cocoons. The ring- 

 like wall between the floor and the roof of the mine is some- 

 what firm but the sheets of silk spun upon the cuticles are 

 very thin and transparent and the slender motile pupae are 

 plainly visible w T ithin. 



The brown-blotch leaf -mine of the witch hazel, L. hamameli- 

 ella, is one of the common miners in regions where its host 

 plant occurs. The larvae make circular or somewhat irregu- 

 lar mines on the upper side of the leaves, two to several 

 larvae inhabiting a single mine. They shear through the 

 upper cells of the leaf in their early stages and in their 

 fourth and fifth stages further extend the mine by the re- 

 moval of thin slices of tissue. At first the mines are whitish, 

 later somewhat brownish and discolored. The excrementi- 



