238 LEAF-MINING INSECTS 



which are evidently constructed for the purpose, may be 

 found either on the same side of the leaf on which the mine 

 occurs, or on the opposite side. Still other puparia are 

 found with the puparial spiracles projecting through the 

 epidermis of the leaf, and some protrude halfway from a 

 slit made at the side of the mine. A few puparia are found 

 attached to the exterior of the leaf, adjacent to the emergence 

 hole. These would probably have fallen to the ground had 

 they not been moist when they issued. Such puparia are 

 often found rigidly attached to the outer surface of the leaf. 



The exit holes made by the larvae in escaping from the 

 leaf add further characters for classifying the mines. Many 

 of the miners, especially those of the Anthomyiidae, make no 

 definite exit holes but break through the parchment-like 

 surface of their mines. The usual type of hole made by the 

 other larvae is a small semicircular slit. The position of 

 these holes varies according to the type of mine; in a blotch 

 mine they are made at the side, and in the linear mine usually 

 at the larger end. Agromyza pusilla Meig., when mining on 

 nasturtium, usually retreats about a quarter of an inch from 

 the end of its burrow and makes a slit parallel to the sides of 

 the mines. As far as is known this is done by no other 

 species. 



Most of the Dipterous leaf-miners apparently pass the 

 winter as puparia. This is particularly true in the three 

 families Agromyzidae, Trypetidae and Anthomyiidae. In 

 some instances the puparia remain in the leaves or in gall-like 

 pockets until the following spring. In other instances the 

 larvae fall to the ground and pupate beneath leaves or other 

 rubbish, or penetrate the ground for a short distance. 



Many of the species have several generations during 

 the summer. Certain Agromyzidae have but a single gen- 

 eration. 



In the Trypetidae and the Anthomyiidae, the adults feed 

 on the surface of plant leaves, sucking up sweetened liquids 



