The mountain ash sawfly, Pristiphora geniculata (Hartig), a 
probable introduction from Europe, was first recorded in North 
America at Haines Falls, New York, in 1926 (635). It is now 
known to occur in New Jersey, New York, Pennsylvania, Michi- 
gan, all of the New England States except Rhode Island, and in 
all eastern provinces of Canada west to Ottawa, Ontario. Its prin- 
cipal hosts are American and European ash. It also occurs occa- 
sionally on showy mountain ash and the hybrid, Sorbaronia hy- 
brida. Full-grown larvae are pale greenish to yellow with yellow 
heads and yellow thoracic legs. All body segments except the last 
are marked with black spots of uneven size and shape (fig. 189). 
The spots occur in irregular rows, four along each side of the 
body and two broken ones down the dorsum. 
In eastern Canada, winter is spent in the prepupal stage. Pu- 
pation occurs in the spring and the adults appear from late May 
to early July. Eggs are deposited in slits cut around the edges of 
leaflets and hatching occurs in about 1 week. Newly-hatched lar- 
vae straddle the edge of the leaf and feed around the periphery. 
When disturbed they raise their abdomens in the form an “’S”. 
Larvae of the first two instars are gregarious. Later, especially 
in the fourth and fifth instars, they often feed singly. They usu- 
ally consume all of a leaflet except the midrib. When they have 
consumed one leaflet they move to another. Feeding is completed 
in about 2 or 3 weeks and the larvae drop to the ground. Here 
they spin cocoons in the duff and top soil. About 20 percent of 
these pupate and appear as second generation adults in July 
(257). 
The mountainash sawfly is primarily a pest of shade and orna- 
mental trees. The esthetic values of these trees is seriously re- 
duced by defoliation, but they usually survive even when com- 
pletely defoliated. 
Other species of Pristiphora occurring in eastern forests in- 
clude P. chlorea (Norton) on oak, P. siskiyouensis Marlatt on 
birch, and P. sycophanta Walsh on willow. 
The yellow-headed spruce sawfly, Pikonema alaskensis (Roh- 
wer), is widespread, occurring from Maine and New Brunswick 
to Idaho, British Columbia and Alaska. Its hosts are white, black, 
red, blue, Norway, and Engelmann spruces (772). Full-grown 
larvae (fig. 190) are olive-green above and lighter green below 
and are about 18 mm. long. The head is chestnut-brown or red- 
dish-yellow and is sometimes mottled with various shades of 
brown. Each side of the body bears a gray-green longitudinal 
stripe near the midline of the dorsum, a broad one beneath this, 
and a darker one farther down. There is also a dark line or spot 
just above the base of each leg. 
In Maine, winter is spent as full-grown larvae in tough, dark 
brown cocoons. Pupation occurs in the spring, and the adults 
appear from late May to mid-June. Eggs are deposited in slits cut 
in current season’s needles, usually at the base and usually only 
one per needle. Sometimes they are also found on tender bark of 
the stem between needles. Young larvae feed on the new needles. 
Older ones move on to and devour the old needles. While feed- 
ing, their rear ends curve downward or upward. The larvae be- 
come full-grown in July and drop to the ground. Here they spin 
459 
