Introduced Pine Sawfly
Contact: Eric Day, Manager, Insect Identification Laboratory
Publication 444-237, August 1996
Introduced Pine Sawfly
Distribution and Hosts
Introduced from Europe in 1914, this pine sawfly
species occurs from S.E. Canada to North Carolina, and west
to the Great Lakes states. It first appeared in the
southern Appalachians in 1977. White pine is the preferred
host, but Scotch, Jack, and red pine are commonly reported
secondary hosts. Virginia and shortleaf pines are also
attacked, but not considered to be threatened.
Description of Damage
The season's first generation larvae feed on old
needles in the upper half of the crown, giving it a thin
appearance. If populations are high, the current year's
foliage may also be consumed. Although trees of all ages
are defoliated, those in the most exposed locations or in
the overstory suffer the most. As a result, branches, and
sometimes an entire tree may be killed. Ornamental,
windbreaks, and Christmas tree plantations are of particular
concern.
Identification
Adults resemble flies and are 7 to 8 mm long, with four
transparent wings. Females lay small oval eggs into slits
in the needles they cut with their sawlike apparatus. They
then cover the eggs with a green frothy substance. Newly
emerged larvae are 6 mm long, with a shiny black head, black
legs, and a yellowish-green body. By the fourth instar, the
larvae have two black lines down their back with numerous
yellow spots. The fifth and sixth instars have a distinct
mottled pattern and can reach 25 mm in length. As with
other sawflies, larvae resemble caterpillars except they
have six or more pseudolegs or prolegs behind the true legs
underneath the abdomen. The last larval instar spins a
cocoon that is cylindrical with rounded ends and relatively
thick, tough walls that vary from light to dark brown in
color. It is the only sawfly that attaches its cocoon to
vegetation, and usually does so in clusters. Pupation
occurs in the cocoons.
Life History
Two generations occur each year and sometimes part of a
third, resulting in overlapping generations. Late instar
larvae overwinter in cocoons and adults emerge in the
spring. Eggs are laid in May and early June and hatch two
weeks later. Young larvae feed gregariously; older larvae
singly. Cocoons are spun during July and August. Second
generation larvae feed through September before spinning
their cocoon. Others complete development and begin the
third generation in the fall, and thus emerge the following
spring as mid-instar larvae.
Control
Natural enemies such as spiders, predacious insects,
rodents, and birds play an important role in reducing high
populations of the introduced pine sawfly. Two imported
parasitic wasps have been effective in holding populations
of this pest at low levels in the sawfly's northern range.
One of these species, Monodontomerus dentipes (Dalman),
through mass rearings and augmentative releases have helped
keep introduced pine sawfly populations low in North
Carolina.
Chemical insecticides are effective in protecting
ornamental plantings and Christmas tree plantations.
Treatment is suggested in June and September when young
trees have five to ten larvae per tree. For registered
chemicals and their formulations, consult the most recent
version of the Pest Management Guide for horticultural and
forest crops, Virginia Cooperative Extension Publication
456-017.
Prepared by S.M. Salom, Department of Entomology, Virginia
Polytechnic Institute and State University, Blacksburg,
Virginia, 24061-0319
References
Anonymous. 1979. Introduced pine sawfly in the South.
USDA For. Serv. For. Bull. SA-FB/P2.
Anonymous. 1989. Insects and Diseases of Trees in the
South. USDA For. Serv. Prot. Rept. R8-PR16. 98 pp.
Drooz, A.T. 1985. Insects of Eastern Forests. USDA For.
Serv. Misc. Publ. #1426. 608 pp.
Skelley, J.M., D.D. Davis, W. Merrill, E.A. Cameron, H.D.
Brown, D.B. Drummond, and L.S. Dochinger (eds.). 1985.
Diagnosing Injury to Eastern Forest Trees. Agric. Inform.
Serv., Coll. of Agric., Penn State Univ.
Weidhaas, J.A. 1989. Insects. pp. 123-136. In J.E.
Johnson (ed.). Christmas Tree Production Manual. Va.
Coop. Ext. Publ. No. 420-075.