568 MISC. PUBLICATION 657, U. S. DEPT. OF AGRICULTURE 
Figure 158.—Mines of Fenusa pusilla in leaves of gray birch. (Courtesy Conn. 
Agr. Expt. Sta.) 
greater part is spent in hibernation in a cell in the ground (Friend, 
168). The eggs are laid in the leaf tissue, the larvae “hatch in a week 
or 10 days and usually complete feeding within the leaf in 1 to 2 
weeks. Full-fed larvae drop to the ground and go through their 
transformation in earthen cells constructed 1 or 2 inches below the 
surface of the soil. Larvae completing their development late in the 
year (August and September) may produce adults the same year, but 
usually they hibernate over winter to produce adults the following 
May. 
Insect parasites affecting the control of this sawfly have not been 
thoroughly investigated. ‘Picking infested leaves from ornamental 
trees would har dly ‘be practical, except possibly in very hght infesta- 
tions and then would be effective only while the larvae are within the 
leaves. It should be borne in mind that this species does not cocoon 
or pass the winter within the leaves. Friend (768) found that nicotine 
sulfate (without soap) diluted in water at the rate of 1: 1,000 killed the 
eggs and many young larvae which had just begun to mine the leaves, 
when both surfaces of the leaves were covered with the insecticide. 
In Connecticut two applications should be made at weekly intervals 
for the first generation, beginning usually between May 20 and May 
25, and three for the second generation, beginning about July 3. 
The elm leaf miner (Fenusa ulmi Sund.) is legless, flattened, and 
whitish, with a greenish cast, and the head is brownish. This leaf- 
mining species is an introduction from Europe and is apparently well 
established in the northeastern part of the United States and the 
southeastern part of Canada. Specific records include Vermont, 
Massachusetts, Connecticut, New York, Michigan, southern Ontario, 
and southern Quebec. Elm is its food plant, chiefly the English and 
Scotch elms, the horticultural variety Camperdown elm, and occasion- 
ally Americanelm. The larvae live in mines made between the upper 
