Author: Scott M. Salom, Virginia Tech
Distribution and Hosts
Diprion similis is a pine sawfly species is native to central Europe. It was introduced to North America in 1914, where it now occurs from S.E. Canada to North Carolina, and west to the Great Lakes states. It first appeared in the southern Appalachians in 1977. Eastern White Pine is the preferred host in North America, but Scots, 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 trees, windbreaks, and Christmas tree plantations are of particular concern.
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.
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.
Natural enemies such as spiders, predatory 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
- 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.
The introduced pine sawfly occurs from Canada to North Carolina, and in the central and lake states. Eastern white pine is its favored host, but it also attacks Scotch, red,jack, and Swiss mountain pines. Infestations of this insect can be very serious in young plantations of white pine grown for timber products or Christmas trees.
Identifying the Insect
A full-grown larva is about 1 inch (25 mm) long, with a shiny, black head. The body has a black stripe on the back and numerous yellow and white spots on the sides. Larvae spin light brown, tough, leathery cocoons on the host tree, other vegetation, and ground litter. Adults resemble flies and are about 3/10 inch (8 mm) long and have four transparent wings.
Identifying the Injury
Defoliation first occurs in the upper crown, giving it a thin appearance. First generation larvae feed on old needles, and later generations feed on both old and new needles, and sometimes on the bark of twigs. Trees in the most exposed locations and in the overstory suffer the most defoliation. Repeated heavy defoliation can cause branch and even tree mortality.
In the southern Appalachians, first generation adults emerge in early spring, about April. Eggs are laid in rows in the needles and covered with a light green substance. Hatch occurs in about 14 days. Larvae feed until cocoons are spun in late June through July. Second generation adults emerge in late July, and most larvae have finished feeding and spin cocoons by late September. There are two generations and sometimes a partial third. As a result of overlapping generations, all life stages can be observed in midsummer.
Introduced and natural enemies play an important role in control of the introduced pine sawfly. Chemical insecticides are effective in protecting ornamental plantings and Christmas tree plantations from defoliation.
Insects and Diseases of Trees in the South. 1989. USDA Forest Service - Forest Health Protection. R8-PR16. 98 pp. Taken from http://fhpr8.srs.fs.fed.us/forstpst.html