The mountain-ash sawfly, P. geniculata (Hartig), a probable introduction from 
Europe, was first recorded in North America at Haines Falls, N.Y., in 1926 (J059). 
It is now recorded from the Northeast to Minnesota, southeast to West Virginia, and 
Newfoundland to Ontario. Its principal hosts are American and European moun- 
tain-ashes. It also occurs occasionally on showy mountain-ash and the hybrid, 
Sorbaronia. 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. 193). 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. Pupation 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 larvae straddle the edge of the leaf and feed around the periphery. When 
disturbed they raise their abdomens in the form of an S. Larvae in the first two 
Stages are gregarious. Fourth and fifth instars often feed singly. They usually 
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 topsoil. About 20 
percent of these pupate and appear as second-generation adults in July (432). 
The mountain-ash sawfly is primarily a pest of shade and ornamental trees. The 
esthetic value of these trees is seriously reduced by defoliation, but they usually 
survive even when completely defoliated. 
Other species of Pristiphora occurring in eastern forests include P. chlorea 
(Norton) on oak, P. siskivouensis Marlatt on birch, and P. sycophanta Walsh on 
willow. 
The yellowheaded spruce sawfly, Pikonema alaskensis (Rohwer), is wide- 
spread, occurring from Newfoundland to Alaska, Massachusetts, Michigan, Min- 
nesota, Wyoming, Idaho and British Columbia. Its hosts are white, black, red, 
blue, Norway, and Engelmann spruces (/320). Full-grown larvae (fig. 194) are 
olive green above and lighter green below and are about 18 mm long. The head is 
chestnut brown or reddish 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. 
Winter is spent as prepupal 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 in the tender bark of the stem 
between needles. There are five feeding instars in males and five or six in females 
(1228). Larvae prefer to feed on new needles, but older larvae will eat old needles 
when new foliage is lacking. No significant differences in the susceptibility of 
white spruce from different seed sources has been found (237). The larvae become 
full grown in early to late July and drop to the ground. Here they spin cocoons in the 
duff or top 2 cm of soil. There is one generation per year (906). 
The yellowheaded spruce sawfly is a serious defoliator of young spruce planta- 
tions and natural reproduction growing in open areas; ornamental, shelterbelt, and 
nursery spruces are also infested. Young plantation trees are usually not attacked 
until the 3rd to Sth year after planting; trees older than 5 years may be killed after 3 
or 4 consecutive years of moderate to heavy defoliation. Small mammals and other 
predators as well as numerous insect parasites are important causes of mortality in 
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