230 LEAF-MINING INSECTS 



and continue their mining habit, apparently not feeding on the 

 surface at all, except as they cut their way into the leaf. In 

 numerous cases, where the obtainable leaves had all been ex- 

 hausted, the larvae bored downward in the stem of the plant. 



When fully developed, the larvae enter the ground to the 

 depth of one-half to one inch and form a silken cocoon, to which 

 bits of soil adhere quite firmly, and there transform. The pupa 

 stage lasts only about seven days, when the adults emerge, a few 

 males in advance, soon after which the sexes pair and oviposit. 



The number of broods varies according to seasonal condi- 

 tions but probably five is normal. 



