COURTESY CONN. AGR. EXPT. STA. 
= FIGURE 187.—Mines of the elm leaf 
Le. miner, Fenusa ulmi, in elm leaves. 
leaving holes in the leaf. The larvae usually become mature in 
late June. Then they vacate their mines and drop to and enter the 
ground to spin their cocoons. There is one generation per year. 
This species appears to be most injurious to small trees in nur- 
series and ornamental plantings. 
The European alder leaf miner, /‘enusa dohrnii (Tischbein), an 
introduced species, occurs in southeastern Canada and through- 
out the Northeastern States. Its hosts are listed as alders, es- 
pecially the introduced European alders. Winter is spent in the 
larval stage in cocoons in the ground. Pupation occurs in the 
spring, and the adults appear and lay eggs during late May and 
early June. The larvae feed in the tissues of the leaf, forming 
blotch mines. Full-grown larvae drop to the ground to pupate, 
and a second generation of adults appears from late July to early 
September. They also lay eggs and give rise to a second generation 
of larvae. These become full-grown by late fall and then enter 
the ground to spend the winter. 
Profenusa thomsoni (Konow), possibly an introduced species 
from the Far East, is widely distributed in southeastern Canada 
and from Maine to Illinois and Wisconsin. Its hosts are gray, 
paper, and yellow birches. In Ontario, female adults were ob- 
served in late July and early August and laid eggs in the tissues 
of leaves. The larvae mined the tissues, forming light-colored, 
blotch mines. Up to 40 larvae were found in a single mine. When 
all of the tissues of a leaf were consumed, all of the larvae, re- 
gardless of age, vacated the mine and dropped to the ground. Of 
these, only those in the latter part of the fifth instar were able to 
enter the soil and survive. In light infestations, sucker growth up 
to about 4 feet tall in shaded locations was preferred. In contrast, 
trees up to 35 feet tall in all types of habitats were attacked in 
heavily infested areas. Damage was not considered severe because 
defoliation occurred late in the season (505). 
Profenusa mainensis Smith, a newly-described species (655), 
has been observed mining the leaves of oak, primarily red oak, in 
Maine during recent years. Full-grown larvae are about 6 mm. 
long and have prognathous, octagonal heads more than twice as 
wide as long. Winter is spent as mature larvae in cells in the duff. 
456 
