24 



LEAF-MINING INSECTS 



away before completing its growth. The little caterpillar, 

 Heliozela aesella, does likewise, in the leaves of grape. By 

 the time it has finished its tenancy the walls of the gall are 

 almost wholly consumed. The sawfly larva that makes 

 the familiar "apple galls" on the leaves of willows when full 

 grown and of larger appetite has to resort to the ordinary 

 use of its jaws, as is evidenced by the large, irregular, frass- 

 filled cavity 3 that it then excavates. 



Fig. 12. Leaf of tulip tree, bearing six mined-out gall of the midge 

 Thecodiplosis liriodendri. 



Stem-boring and bast-mining and leaf-mining are habits 

 closely akin. Stem-boring probably came first since the 



8 The case of the leaf-mining fly of the iris Agromyza laterella as detailed 

 by Claassen (1918) is quite different, and quite unique. This larva is a true 

 leaf-miner. W T hen grown it bores down into the undeveloped iris bud to 

 form a pupation chamber. The presence of the pupa there when growth 

 starts in the spring, causes a gall to develop; but its development is quite 

 incidental: it profits the fly nothing. 



