22 LEAF-MINING INSECTS 



mental life of the insect. Here again, permanence of resi- 

 dence within a single mine is a sign of better adaptation to 

 the leaf -mining life. 



Some of the less specialized leaf maggots seem to slip in 

 and out of a soft leaf at will. Encountering a vein, they cut 

 a slit in the epidermis and slip out through it ; and, presently 

 in a new place, cut another slit and slip into the leaf again. 

 The locust leaf-mining beetle, Chalepas dorsalis, regularly 

 occupies several leaflets in succession; when it has finished 

 the mesophyll in one leaflet it rambles off in search of another 

 one. The grass leaf -miner, Aphelosetia orestella, occupies 

 one leaf of bottle-brush grass, Hystrix patula, in the late 

 season and hibernates in it; but this old leaf is frozen in the 

 winter, and in the spring the larva enters a new leaf and 

 completes its growth there. Others of this genus have 

 similar habits. 



This subject will receive special treatment in our dis- 

 cussion of the order Lepidoptera, in which order all the 

 grades of tenancy are best illustrated; but here it may be said 

 that most leaf-mining larvae spend their entire larval life 

 within a single mine, and many pupate there, either with or 

 without a cocoon, and either attached to the wall or free. 

 More often the pupa is formed outside, in a crevice or a 

 fold of the leaf or in the ground. 



THE ORIGIN OF THE LEAF-MINING HABIT 



It is probable that the leaf -mining habit has been ac- 

 quired independently many times. The Buprestid beetles 

 may well have come to it through their wood-boring 

 habit. Many of them live in succulent twigs and originally 

 they may have come into the leaf blade by way of the stalk. 

 At any rate, their earlier stages are more typically of the 

 form of body of the wood borers and the later stages are 

 more cylindric. The mines are often started upon the 

 surface of a vein. 



