194 



LEAF-MINING INSECTS 



let, the margins becoming very thin and the central mound 

 about half a millimeter in thickness. A hardened, trans- 

 parent, mucilaginous secretion glues each egg to the leaf. 



The larva eats its way through the attached side of the 

 egg directly into the leaf. The longitudinal ribs on the leaf 

 surface are just far enough apart to allow the flat larva to 

 pass between, and enter the mesophyl. There are three 



Vi 



Fig. 61. Leaf of Scirpus Uuviatilis with mine of Taphrocerus gracilis. 

 A, upper; B, lower side; e, egg-shell. 



larval instars. In the first the form is of a typically Bupres- 

 tid, flattened "tadpole" outline; in later stages it becomes 

 more cylindrical. In all three the wedge-shaped head is 

 deeply sunk in the flattened and heavily chitinized prothorax. 

 Toward the last larval instar a pair of prolegs of a rudi- 

 mentary unarmed sort develops at the rear end of the ninth 

 abdominal segment. 

 The larva mines first in one direction and then in the 



