INSECT ENEMIES OF EASTERN FORESTS 569 
and lower surfaces of the leaves, feeding on the parenchyma between 
the veins, thus causing large blotch or blisterlike mines (fig. 159). 
Several larvae may mine in a single leaf. In light infestations the 
injured epidermis soon dries, turns brown, and drops out, and in se- 
vere infestations the mined leaves fall prematurely. Small trees in 
crnamental and nursery plantings seem to be most seriously attacked, 
although occasionally heavy infestations occur on the larger trees. 
There is one generation annually. The adults emerge in May, usually 
during the first half of the month. The eggs are deposited in the 
leaf tissue and hatching takes place in about a week. The larvae 
usually become full grown during the latter half of June when they 
vacate their mines, drop to the ground, and spin brown papery cocoons 
in the topsoil. Winter is passed as prepupal larvae in the cocoons, and 
transformation to the pupal and adult stages takes place in the spring. 
The European alder leaf miner (Fenusa dohrnii (Tisch.) ), closely 
allied to F. ulmi, is a European species which was accidentally intro- 
FicurE 159.—Mines of Fenusa ulmi in elm leaves. (Courtesy Conn. Aer. 
Expt. Sta.) 
