in the Northeastern States and southeastern Canada. Its hosts are 
various species of birch, with gray, paper, yellow, and European 
white being preferred. The full-grown larva is somewhat flattened 
and whitish, with the head and joints of the thoracic legs brown- 
ish, and is about 10 mm. long. 
In Maine, winter is spent in the larval stage and pupation 
occurs in late spring. Female adults (no males have been found) 
appear during June and early July and deposit their eggs singly 
in slits cut in the edges of mature leaves, apparently at all levels 
in the tree. The larvae feed in the tissues between the upper and 
lower surfaces of the leaf, producing large blister-like or blotch 
mines free of frass (fig. 185). Each full-grown larva constructs a 
cocoon or hibernaculum within its mine. The leaf then falls to the 
ground and the larva remains in its hibernaculum throughout the 
winter. There is one generation per year (591). 
Heavy infestations of the birch leaf-mining sawfly occurred in 
Maine during the 1920’s and 30’s, and severe defoliation of birch 
occurred in many areas. Very little tree mortality occurred, but 
there was a considerable loss in annual growth. During this 
period several species of parasites were imported against the 
sawfly (204), two of which, Kratochviliana laricinellae (Ratze- 
burg) and Phanomeris phyllotomae Muesebeck, became 
established. 
The birch leaf miner, Fenusa pusilla (Lepeletier), an introduced 
species first recorded from North America in Connecticut in 1928, 
now occurs in southeastern Canada and from Maine to New Jer- 
sey and west to Ohio and the Lake States. Full-grown larvae are 
somewhat flattened, yellowish-white in appearance, and about 6 
mm. long. Black spots occur on the venter of the thorax and the 
first abdominal segment. 
F-519525 
FIGURE 185.—Mines and hi- 
ee? bernaculae of Heterarthrus 
‘ie, ot, nemoratus, the birch leaf- 
ee mining sawfly, in leaf of 
paper birch. 
454 
