2G0 LEAF-MINING INSECTS 



ing movements of the abdomen the epidermal leaf tissue is 

 punctured. The ovipositor is then forced by repeated 

 thrusts to its full length between the upper and lower layers 

 of the leaf, the egg quickly deposited, and the ovipositor 

 withdrawn to its normal position. Only one egg is depo- 

 sited in a puncture, but the fly repeats the process of oviposi- 

 tion a number of times in a given day. Frequently she ovi- 

 posits into what are apparently small feeding punctures. 



Eggs may be deposited either from the upper or lower side 

 of the leaves, but the majority of them are deposited from 

 the upper side. They are placed with the longer axis of the 

 egg parallel to the veins of the leaves. 



The larva, when ready to emerge, ruptures the cephalic 

 end of the egg shell and immediately begins to feed on the 

 green tissues of the leaf. The mine at first is very small and 

 threadlike, scarcely noticeable to the unaided eye. The 

 diameter of the mine increases as the larva increases in size, 

 and by the time the larva reaches maturity the mine may be 

 greatly widened. In large plants, with long, wide leaves, 

 the larvae frequently makes mines from 15 to 20 inches in 

 length. Such mines are usually linear in outline, and al- 

 though they run from side to side, the turns are less frequent 

 than when larvae mine in short leaves of smaller plants. In 

 the latter the larvae traverse the leaves oftener. They fre- 

 quently make side galleries diagonally across the leaves, 

 then retreat and continue the main mine down the blade. 



A number of these galleries are often found leading away 

 from one mine in a leaf. All sorts of peculiarly shaped 

 mines are made in leaves, especially in small plants or in 

 plants with a limited amount of leaf surface. Some of these 

 mines show almost perfect loops, while others traverse the 

 leaves in snakelike fashion. 



In young oats and barley the larvae apparently break 

 away from the accustomed habit of making thread-like mines 

 and instead appear to undermine almost the entire upper 



