236 LEAF-MINING INSECTS 



other hand, make large, messy blotch mines in the leaves 

 which wilt as a result of their attack. 



The larvae of Agromyzidae affect the leaves in different 

 ways. Some produce tortuous mines which at times make 

 very beautiful patterns on the leaves. If these larvae be- 

 come abundant they may kill the plant outright, especially 

 if the mines are deep and large. The larvae that mine the 

 thinner leaves cause them to wilt. If the mines are shallow, 

 the growth of the leaf may not be affected. Some larvae 

 cause a part of the leaf to wilt while the rest remains turgid, 

 with the results that the leaf becomes distorted. Other 

 species attack the unfolding leaves, giving them a wrinkled 

 or fluted appearance. Such a condition is described under 

 Agromyza later ella. 



Thefrass. The arrangement of the frass in certain mines 

 is very characteristic. In the mine of Phytomyza nigritella 

 on peach and cherry, the frass is arranged in a distinct line 

 of spots: no other dipterous or lepidopterous mine could 

 be confused with it. The mine of Phytomyza albiceps bred 

 from aster and goldenrod, has the frass in a prominent cen- 

 tral line, resembling a lepidopterous mine in this respect ; on 

 other hosts, however, the mine of this species often has an 

 indistinct frass line. In the remainder of the Diptera the 

 frass is arranged in indistinct lines or is scattered about 

 the mine. 



The puparia. The position of the puparium has been 

 found constant for each species. Most of the larvae, on 

 maturing, cut a slit in the side of the mine, through which 

 they escape. In some species the puparium is formed in 

 the ground or beneath leaves or rubbish. In many species 

 the larva transforms within the leaf and the puparium has a 

 definite place in the mine. Some puparia are found loose 

 within the mine, while others are attached to the upper or 

 lower epidermis by means of a pellet of frass. Some are 

 found in side channels to the main mine. These channels, 



